The influence of muscle strength and aerobic fitness on functional recovery in elite female soccer players

BACKGROUND

We examined the influence of muscle strength and aerobic fitness on wellbeing and muscle function recovery in female soccer players.

METHODS

Sixteen players from the English Women's Super League (age: 26±4 yrs; height, 1.70±0.07 m; mass, 67.9±6.4 kg) completed an isometric mid-thigh pull test (IMTP) and maximal aerobic speed test (MAST). Using a median split, players were divided by strength into high (H-IMTP) and low (L-IMPT) groups and by fitness into high (H-MAST) and low (L-MAST) groups. Countermovement jump height (CMJ), Reactive Strength Index (RSI) and wellbeing were measured 2 days prematch, then 3 subsequent days post-match (M+1, M+2, M+3).

RESULTS

In H-IMTP, CMJ, RSI and wellbeing were higher at M+1-M+3 (P<0.05). At M+3, CMJ in H-IMTP was 30.3±3.5 cm vs. 26.2±3.4 in L-IMTP. CMJ and wellbeing were unaffected by fitness, but RSI was lower at M+1-M+3 in the L-IMTP group (P<0.05).

CONCLUSIONS

In conclusion, isometrically stronger but not aerobically fitter female soccer players recover quicker after matches.

Let´s Swing it -The Interaction Between Participation-Related Shoulder Load and Pre-season Trunk Rotation Power on Shoulder Problems in Male Handball Players

Background

Little is known about the influence of kinetic chain strength and power on shoulder problems in handball players or the impact of participation-related shoulder load (PSL) during a season. Suboptimal activity of the kinetic chain during throwing might make the shoulder more vulnerable.

Purpose

The purpose of this study was to assess 1) the association between pre-season measurements and shoulder problems among handball players and 2) whether pre-season strength and power influence the association between PSL and severity of shoulder problems.

Study Design

Prospective observational cohort study.

Methods

Pre-season measurements were done using the Isometric mid-thigh pull for lower body strength, a seated test for trunk rotation power (TRP) and isometric testing of external (ER) and internal rotation shoulder strength on 42 male players. Shoulder problems (prevalence, substantial prevalence, and severity score) were documented weekly through a season (31 weeks) with The Oslo Sports Trauma Research Center Overuse Questionnaire (OSTRC-O2) and PSL with the modified Borg rate of perceived exertion scale. Spearman´s correlation coefficient was applied to examine the association within the first aim, while a mixed model ANOVA was conducted to analyze the second aim.

Results

A weak and negative correlation (rs=-0.34) was found between pre-season ER strength and the individual prevalence of shoulder problems (p=0.029). A main effect was found between PSL and the OSTRC-O2 severity score (p=<0.001) with higher severity scores observed with increased PSL. A significant interaction was found between PSL and pre-season TRP regarding their influence on the OSTRC-02 severity score (p=0.017). With higher PSL, a higher severity score was observed among players with pre-season TRP more than one standard deviation below the group's mean.

Conclusions

The results indicate that low TRP may make the throwing shoulder more vulnerable to an increase in load. Looking beyond shoulder strength and load may therefore be important.

Level of evidence

3.

Are caffeine effects equivalent between different modes of administration: the acute effects of 3 mg.kg-1 caffeine on the muscular strength and power of male university Rugby Union players

BACKGROUND

There is growing interest in the potential of alternative modes of caffeine administration for enhancing sports performance. Given that alternative modes may evoke improved physical performance via distinct mechanisms, effects may not be comparable and studies directly comparing the erogenicity of alternative modes of caffeine administration are lacking. To address this knowledge gap, the present study evaluated the effect of 3 mg·kg-1 caffeine delivered in anhydrous form via capsule ingestion, chewing gum or mouth rinsing on measures of muscular strength, power, and strength endurance in male Rugby Union players.

METHODS

Twenty-seven participants completed the study (Mean ± SD: Age 20 ± 2 yrs; daily caffeine consumption 188 ± 88 mg). Following assessments and reassessment of chest press (CP), shoulder press (SP), Deadlift (DL), and Squat (SQ) 1-repetition maximum (1RM) and familiarization to the experimental procedures, participants completed six experimental trials where they were administered 3 mg.kg-1 caffeine (Caff) or placebo (Plac) capsule(CAP), chewing gum(GUM) or mouth rinse(RINSE) in a randomized, double-blind and counterbalanced fashion prior to force platform assessment of countermovement jump, drop jump and isometric mid-thigh pull performance. Strength endurance was measured across two sets of CP, SP, DL, and SQ at 70% 1RM until failure. Pre-exercise perceptions of motivation and arousal were also determined.

RESULTS

Caffeine increased perceived readiness to invest mental effort (p = .038; ηp2=.156), countermovement jump height (p = .035; ηp2=.160) and SQ repetitions until failure in the first set (p < .001; d = .481), but there was no effect of delivery mode (p > .687; ηp2<.015). Readiness to invest physical effort, felt arousal, drop jump height, countermovement jump, drop jump and isometric mid-thigh pull ground reaction force-time characteristics and repetitions until failure in CP, SP and DL were not affected by caffeine administration or mode of caffeine delivery (p > .0.052; ηp2< .136).

CONCLUSION

3 mg.kg-1 caffeine administered via capsule, gum or mouth rinse had limited effects on muscular strength, power, and strength endurance. Small effects of caffeine on CMJ height could not be explained by changes in specific ground reaction force-time characteristics and were not transferable to DJ performance, and effects specific to the SQ RTP exercise underpin the complexity in understanding effects of caffeine on muscular function. Novel modes of caffeine administration proposed to evoke benefits via distinct mechanisms did not offer unique effects, and the small number of effects demonstrated may have little translation to a single performance trial when data examining direct comparison of each caffeine vehicle compared against a mode matched placebo is considered.

Force-velocity-power variables derived from isometric and dynamic testing: metrics reliability and the relationship with jump performance

We investigated the convergent validity and intrasession reliability of force, velocity, and power (FVP) variables and the dynamic strength index (DSI) obtained from isometric midthigh pull (IMTP) and squat jump (SJ) testing. Fifteen male combat sports athletes (27 ± 5 years, 77 ± 9 kg, 1.76 ± 0.1 m, 14 ± 6% body fat) participated in a 2-days study. The first day involved testing familiarization, while the second was dedicated to IMTP and SJ testing. Maximal isometric force (Fiso ) was obtained from IMTP, while mean force, mean velocity, jump height, and jump impulse (J) were gathered from SJ. To analyze the FVP, we calculated the linear relationship between force and velocity, which allowed us to obtain the slope of the relationship (SFV ), the theoretical velocity at zero force (V0 ), and the theoretical maximal power (Pmax ). DSI was obtained as a ratio from SJ peak force and Fiso . The convergent validity was investigated using Spearman's ρ coefficients to assess the relationships between jump height and J with Fiso , V0 , SFV , Pmax , and DSI. The intrasession reliability was assessed using intraclass correlation coefficients (ICC) and coefficient of variations (CV). All variables demonstrated acceptable reliability scores. ICC ranged from moderate to excellent, and the mean CV was <10%. We found a "very large" correlation between jump J and Pmax , while jump height was not correlated with any variable. In conclusion, the IMTP and SJ combination is a practical way to determine FVP producing capacities that can be reliably measured (intrasession). The Pmax , derived from FVP, was correlated with jump performance, which might evidence the convergent validity of the method.

The Effects of Mental Fatigue Induced by the Stroop Test on Muscular Endurance Performance and Neuromuscular Activation in Division III Female Athletes

The purpose of this study was to investigate the effect that mental fatigue, as induced by a Stroop test, has on resistance training performance outcomes such as muscular endurance, power output, and neuromuscular activation. Seven female college-aged NCAA Division III student-athletes with at least one year of resistance training experience and were within the 50th percentile for maximal aerobic capacity provided informed consent for participation. During two separate visits, using a within-subject crossover experimental design, subjects completed either the experimental or control condition. Subjects then completed a to-failure leg press test at 50% of their 1-repetition maximum (1RM) followed by an isometric midthigh pull (IMTP) attempt with electromyography (EMG) analysis. The experimental condition consisted of a 30-minute Stroop test, while the control condition consisted of watching 30 minutes of a sitcom. Both activities were completed while cycling at 40% of their aerobic capacity. A NASA Task Load Index (TLX) inventory was administered following the completion of each cycling session to determine the perceived workload and mental fatigue of each activity. While the mentally fatiguing condition was significantly more mentally fatiguing (p = 0.02) than the control condition, mental fatigue did not statistically affect any of the evaluated performance outcomes (p>0.05). These findings suggest that mental fatigue, a common symptom of psychological stress, does not affect resistance-training-related performance outcomes among female athletic populations.

A comparison of manual and automatic force-onset identification methodologies and their effect on force-time characteristics in the isometric midthigh pull

The aim of this study was to assess the agreement of three different automated methods of identifying force-onset (40 N, 5 SDs, and 3 SDs) with manual identification, during the isometric mid-thigh pull (IMTP). Fourteen resistance-trained participants with >6 months experience training with the power clean volunteered to take part. After three familiarisation sessions, the participants performed five maximal IMTPs separated by 1 min of rest. Fixed bias was found between 40 N and manual identification for time at force-onset. No proportional bias was present between manual identification and any automated threshold. Fixed bias between manual identification and automated was present for force at onset and F150. Proportional but not fixed bias was found for F50 between manual identification and all automated thresholds. Small to moderate differences (Hedges g = -0.487- -0.692) were found for F90 between all automated thresholds and manual identification, while trivial to small differences (Hedges g = -0.122--0.279) were found between methods for F200 and F250. Based on these results, strength and conditioning practitioners should not use a 40 N, 5 SDs, or 3 SDs threshold interchangeably with manual identification of force-onset when analysing IMTP force-time curve data.

Physical and technical attributes associated with on-water rowing performance in junior and elite rowers

On-water rowing performance consists of the integration of physical and technical attributes. This exploratory study aimed to describe key physical and technical variables for elite and junior rowers and examine the associations and predictive capacity of these variables with on-water rowing performance outcomes. Twenty-eight junior (16 females, 16 ± 0.8 years and 12 males, 17 ± 0.7 years) and 24 elite rowers (12 females, 24 ± 2.7 years and 12 males, 27 ± 2.6 years) completed an on-water, single sculling biomechanics assessment combined with a series of physical, strength and power tests. Elite men and women were superior in mean gate force, distance per stroke and recovery distance compared to junior groups as determined by independent t-tests and effect size appraisal (p < 0.017, d > 1.2). Large associations (p < 0.01) were evident between anthropometry, strength and power assessments with the on-water measures of catch angle, mean gate force, recovery distance and boat speed. Differences in ROM and flexibility attributes did not distinguish between elite and junior rowers. Linear discriminant analysis revealed that individual rowers can be appropriately categorised by sex and performance level based on their physical and technical attributes. This battery of testing with world-class athletes represents an excellent level of ecological validity for the assessment of rowers pertinent to on-water performance.

High Cognitive Effort Prior to Velocity-Based Training Sessions Reduces Rate of Force Development but Not Maximum Strength Gains in Untrained Male Adults

This study aimed to analyze the chronic effect of high cognitive effort immediately before resistance exercise sessions on neuromuscular performance in untrained male adults. We used a mixed experimental design, with the group as between-participants factor and time as within-participants factor. Thirty-four participants were randomly assigned to two parallel groups: high cognitive effort (n = 17) and control (n = 17). Subjects in the control group were seated for 30 min before the resistance exercise sessions, while the high cognitive effort group completed incongruent trials of the Stroop task until subjective mental fatigue was present immediately before resistance exercise sessions. Participants attended 45 sessions over 15 weeks, consisting of three familiarizations, three baseline evaluations, 36 velocity-based training sessions, and three postexperiment evaluation sessions. Rate of force development (RFD) during the isometric mid-thigh pull, half back-squat 1-RM, and countermovement jump (CMJ) were measured before and after the 12-week intervention. A significant group × time interaction effect was found for the average RFD at 0-250 ms (p < 0.05), with greater improvements for the control group than for the high cognitive effort group. There was no group × time interaction for half back-squat 1-RM (p > 0.05). Also, there was no group × time interaction for CMJ (p > 0.05). In conclusion, repeated high cognitive effort immediately prior to resistance exercise sessions is a phenomenon that can induce greater early velocity loss and, consequently, impairs the improvements in RFD. However, this did not inhibit the increased performance for explosive strength and CMJ in male untrained adults. High cognitive effort before resistance exercise sessions should be avoided.

Kinetic Predictors of Weightlifting Performance in Young Weightlifters

ABSTRACT

Morris, SJ, Oliver, JL, Pedley, JS, Radnor, JM, Haff, GG, Cooper, S-M, and Lloyd, RS. Kinetic predictors of weightlifting performance in young weightlifters. J Strength Cond Res 38(9): 1551-1560, 2024-Relationships between force-generating capabilities and weightlifting performance ( e.g ., snatch, clean and jerk [C&J], and combined total) have previously been explored in adult weightlifters; however, associations in young athletes are unknown. The purpose of this study was twofold: (a) to examine the relationships between countermovement jump (CMJ) and isometric midthigh pull (IMTP) kinetics and weightlifting performance in young weightlifters and (b) to determine the proportion of weightlifting performance that could be accounted for by CMJ and IMTP kinetics using principal component analysis (PCA). Thirty-seven young weightlifters (12-18 years of age) completed 3 trials of CMJ and 2 trials of the IMTP assessments on dual force plates. Recent competition maximum loads, obtained within 2 weeks of the data collection, for the C&J and snatch were also recorded. Pearson's zero-order correlation coefficients demonstrated moderate to very high correlations ( r = 0.359-0.801; all p ≤ Benjamini-Hochberg critical values [ B-Hα ]) between CMJ kinetic variables, including jump height, average braking force, average braking velocity, absolute and relative braking net impulse, absolute and relative force at minimum displacement, absolute and relative propulsive force, absolute and relative propulsive net impulse and average propulsive velocity, and weightlifting performance. High to very high correlations were evident between IMTP peak force and relative peak force and all weightlifting performance metrics (snatch, C&J, combined total, combined total [kg]/body mass [kg -0.67 ], and Sinclair's total; r = 0.538-0.796; p ≤ B-Hα ). Components from the PCA were used to conduct stepwise, multiple, linear regression analyses. Moderate (45.8-52.9%) and large percentages (79.1-81.3%) of variance in absolute measures of weightlifting performance were explained by IMTP peak force variables and CMJ propulsive variables, respectively. These novel findings indicate that IMTP peak force variables and CMJ propulsive variables could provide valuable insight for talent identification and long-term athletic development in junior weightlifting pathways.

Test-retest reliability of a single isometric mid-thigh pull protocol to assess peak force and strength-endurance

The purpose of this study was to examine the test-retest reliability of strength-endurance protocols using isometric mid-thigh pull (IMTP). Twenty-eight participants (23.2 ± 4.9 years) completed two protocols across four testing sessions. Protocol one consisted of 10 maximal IMTP tests lasting 5 seconds each with 10 seconds rest between. Protocol two consisted of a prolonged 60 second maximal IMTP. Data from protocol 1 was analysed in two ways; (a) use of the highest peak value from the first three IMTP efforts, and the lowest peak value from the final three IMTP efforts, and (b) use of the mean peak force from the first three IMTP efforts and mean peak force from the final three IMTP efforts. Data from protocol two used the highest and lowest peak values in the first- and final-15 seconds. Analyses revealed excellent reliability for peak force across all four testing sessions (ICC = 0.94), as well as good test-retest reliability for strength-endurance for protocol 1 (a; ICC = 0.81, b; ICC = 0.79). Test-retest reliability for protocol 2 was poor (ICC = 0.305). Bland-Altman bias values were smaller for protocol 1(a = -8.8 Nm, b = 21.7 Nm) compared to protocol 2 = (119.3 Nm). Our data suggest that 10 maximal IMTP tests performed as described herein is a reliable method for exercise professionals to assess both peak force and strength-endurance in a single, time-efficient protocol.

Concurrent validity and test-retest reliability of VALD ForceDecks' strength, balance, and movement assessment tests

OBJECTIVES

To evaluate the concurrent validity and test-retest reliability of common movement, strength, and balance tests using portable uniaxial dual force plates.

DESIGN

Repeated measures cross-sectional study.

METHODS

Sixteen healthy individuals participated in two testing sessions, where they performed 12 different movement, strength, and balance tests. Vertical ground reaction force and centre of pressure data were collected using the VALD ForceDecks simultaneously with ground-embedded laboratory force plates. Concurrent validity was assessed using root mean square error for raw time-series data and Bland-Altman plots for discrete metrics. Test-retest reliability was assessed using intraclass correlation coefficients and minimal detectable changes.

RESULTS

ForceDecks recorded vertical ground reaction forces and center of pressure with high accuracy compared to laboratory force plates. The mean bias between systems was negligible (<2 N or 0.1 mm), with small limits of agreement (<5 N or 1 mm). Overall, 530/674 (79%) showed good or excellent validity (<10% difference) and 611/773 (79%) had good or excellent reliability (intraclass correlation coefficient >0.75). ForceDecks reliability was similar to laboratory force plates (<0.07 intraclass correlation coefficient median difference for all metrics).

CONCLUSIONS

Portable uniaxial force plates record highly accurate vertical ground reaction forces and center of pressure during a range of movement, strength, and balance tests. The VALD ForcDecks are a valid and reliable alternative to laboratory force plates when strict standardized testing and data analysis procedures are followed. Users should be aware of the validity and reliability characteristics of the tests and metrics they choose.

Between-Session Reliability of Athletic Performance and Injury Mitigation Measures in Female Adolescent Athletes in the United States

Adolescence is a fundamental period for female athletes to develop athletic performance, mitigate injury risk, and gain collegiate sport scholarships, but there is also a high incidence of sport-related injuries. Physical profiling and athlete screening can support the individualisation of training programmes; however, there is a lack of data pertaining to the reliability of athletic performance and injury surrogate measures in adolescent female athletes. The aim of this study was to quantify the between-session reliability of an athletic performance and injury mitigation testing battery in female adolescent athletes. A total of 31 post-peak height velocity (PHV) (3.00 ± 0.82 years) female athletes (age: 16.20 ± 1.20 years; standing height: 166.00 ± 6.00 cm; mass: 65.5 ± 10.70 kg) from various sports (track and field = 1; lacrosse = 2; basketball = 2; soccer = 3; softball = 11; volleyball = 12) completed two sessions of a multicomponent testing battery 48 h to 1 week apart including the assessment of 33 measures addressing lower-limb isometric strength, eccentric strength, reactive strength, linear sprint and change of direction speed, and lower limb control. Of the 33 measures, between sessions, 29 had a high to nearly perfect intraclass correlation coefficient (ICC) (0.508-0.979), and 26 measures were not statistically significantly different between sessions (p ≤ 0.05). All measures demonstrated low to acceptable coefficient variation (CV%) (0.61-14.70%). The testing battery used can be utilised for recruitment and longitudinal monitoring within sports organisations for female adolescent athletes.

Changes in isometric mid-thigh pull peak force and symmetry across anterior cruciate ligament reconstruction rehabilitation phases

Background

Whether functionally relevant strength assessments, such as the isometric mid-thigh pull (IMTP), can be used either bilaterally or unilaterally to evaluate and guide rehabilitation progress in those with anterior cruciate ligament reconstruction (ACLR) is under-researched. This study assessed changes in peak force (PF) and asymmetry across 3 phases for bilateral and unilateral IMTP assessments in patients with ACLR. Peak isometric force from the IMTP was compared to peak torque from isokinetic dynamometry as well as against a cohort of healthy, uninjured individuals.

Method

Participants (ACLR, n = 15) completed bilateral and unilateral IMTP assessments at weeks 12 (baseline), 16 (phase 3), and 20 (phase 4) of rehabilitation to evaluate changes in PF and asymmetry. Asymmetry was evaluated using the asymmetry angle. Isometric data from the IMTP were compared to that from an isokinetic dynamometer as well as against a cohort of healthy, uninjured participants (n = 63) allowing for a detailed analysis of limb-specific force production.

Results

The PF during the bilateral IMTP increased for both the injured (0.94 N/kg) and uninjured (0.26 N/kg) limbs from baseline to phase 4, whereas the PF of the injured limb increased by 1.5 N/kg during the unilateral IMTP in the same time frame. Asymmetry values systematically reduced by ∼1% and ∼0.5% for the bilateral and unilateral IMTP tests from baseline to phase 4. Significant differences in PF of the injured limb were evident between those with ACLR and healthy controls across all phases (p = 0.022-0.001). The rate of progression in PF capacity was dependent on test type, amounting to 0.1 and 0.2 body weights per week for the bilateral and unilateral IMTP respectively. Small-to-large correlations (r = 0.12-0.88) were evident between IMTP PF and peak torque from the isokinetic dynamometer as well as between asymmetry metrics from both tests.

Conclusion

The findings suggest that IMTP PF has potential for monitoring changes in PF and asymmetry during the ACLR rehabilitation progress. Both injured limb and uninjured limb show improvement in force-generating capacity, implying a positive adaptation to rehabilitation protocols. The findings highlight that ACLR is a unilateral injury that requires bilateral rehabilitation.

The Value of Strength as a Predictor of Musculoskeletal Injury in Canadian Armed Forces Basic Infantry Candidates

INTRODUCTION

Musculoskeletal injuries (MSKI) impact military organizations by threatening their operational readiness, warranting investigation into relevant factors to inform risk reduction strategies. While several self-reported and physical performance measures have been associated with MSKI among military personnel, few have been validated and none have been reported in Canadian basic infantry candidates. The purpose of this study was to investigate associations between self-reported and physical performance measures and MSKI, and determine their validity as predictors of MSKI, in Canadian basic infantry candidates.

METHODS

This was a planned secondary analysis of a study tracking MSKI at a basic infantry training facility in Ontario, Canada approved by Defence Research & Development Canada. Before the basic infantry training, consenting candidates completed a baseline testing session including self-reported questionnaires, measures of anthropometry, and physical performance previously associated with MSKI (ankle dorsiflexion test, Y-Balance Test, Isometric Mid-Thigh Pull, and the Fitness for Operational Requirements of CAF Employment (FORCE) evaluation). All MSKI reported by candidates were diagnosed by licensed healthcare providers. From a total sample of 129 candidates, 76% (n = 98) were used to determine any associations between baseline testing variables and MSKI and to develop a predictive model (Development Sample), while 24% (n = 33) were used to offer preliminary validation of the same predictive model (Validation Sample). The binary logistic regression and independent sample t-testing determined independent associations with MSKI in the Development Sample. All continuous variables and dichotomous variables previously associated with MSKI risk (Smoker Yes/No, previous history of MSKI, and physical inactivity) were entered into a backward stepwise logistic regression analysis to assess the predictive association with MSKI incidence in the Development Sample. The regression model was then applied to the Validation Sample.

RESULTS

A total of 35 MSKI were diagnosed by Health Services Centre staff. The majority of the MSKI were acute (63%), sustained to the hip, knee, and ankle (74%). The most common diagnoses were strains and sprains (71%). Uninjured participants performed significantly better on the Relative Isometric Mid-Thigh Pull, FORCE 20 mR, FORCE ILS, and FORCE Estimated VO2peak compared to injured participants. Logistic regression analysis showed that the only variable with significant independent association with diagnosed MSKI incidence was self-reported previous history of MSKI. However, the backward stepwise logistic regression analysis retained self-reported previous history of MSKI, FORCE SBD, FORCE Estimated VO2peak, and Isometric Mid-Thigh Pull Peak Force as predictors of MKSI. The logistic regression model including these variables could predict MSKI with an accuracy of 79% in the Development Sample and 67% in the Validation Sample.

CONCLUSION

This study provides preliminary support for the value of measures of absolute muscular strength and cardiorespiratory fitness as predictors of MSKI in Canadian basic infantry candidates. Given the associations between physical performance measures and MSKI, and their necessity during occupational tasks, it is recommended that Canadian basic infantry training facilities integrate resistance training with external loads to best prepare their candidates to meet their occupational demands and potentially minimize MSKI. Further investigations to confirm the predictive capacity of these variables in a larger sample across additional facilities are warranted.

"You Are Not Wrong About Getting Strong:" An Insight Into the Impact of Age Group and Level of Competition on Strength in Spanish Football Players

OBJECTIVE

This study aimed to compare the maximum and rapid force production of Spanish football players and explore the differences between age group and level of competition.

METHODS

A cross-sectional study was developed to evaluate the peak force (PF), relative PF, and rate of force development over 250 ms (RFD0-250) during the isometric midthigh pull between groups of football players based on age group (senior vs junior) and level of competition (national vs regional). Using a portable isometric rig, 111 football players performed 2 isometric midthigh-pull trials on a force plate. Two-way analysis of variance with Bonferroni post hoc correction was applied, and statistical significance was set at P ≤ .05. The PF, relative PF, and RFD0-250 0, 25, 50, 75, and 100 percentiles were also calculated and descriptively reported, separated by age group and level of competition.

RESULTS

The analysis of variance revealed a significant main effect of the level of competition for the PF (P < .001), relative PF (P = .003), and RFD0-250 (P < .001). There was a significant main effect of age group for the PF (P < .001). There was a significant interaction effect of the age group × level of competition for relative PF (P = .014). National players were stronger than regional players on the PF and RFD0-250 (P < .001). Senior players were stronger than junior players for the PF (P < .001).

CONCLUSIONS

Maximum and rapid force production are crucial for Spanish football players as they progress in both level of competition and age group. Practitioners should encourage young football players to prioritize strength development to improve their athletic performance.

Comparison of resistance training vs static stretching on flexibility and maximal strength in healthy physically active adults, a randomized controlled trial

BACKGROUND

The aim of the present study was to compare the effects of resistance training through full range of motion and static stretching (SS) of the hip and lower back extensors on flexibility and strength in healthy, physically active, adults.

METHODS

Eighteen participants (age: 24.2 ± 3.0 years, body mass: 71.3 ± 8.9 kg, height: 172.8 ± 7.5 cm) were randomly assigned to either a Resistance Training (RT) (n = 6), SS (n = 6), or control (CON) group (n = 6). The sit & reach (S&R) flexibility test and maximum isometric straight legged deadlift (ISLDL) at 95% and 50% range of motion (ROM) were tested pre- and post-intervention with significance set at p < 0.05. Both groups conducted four to eight sets per session. Within each set, the RT group performed eight repetitions each lasting four seconds, while the SS group stretched continuously for 32 s. The rest periods between each set were 60-90 s. Consequently training volume and rest times were matched between the groups.

RESULTS

The RT and SS groups achieved significant, large magnitude improvements in the S&R test compared to the CON group (p < 0.01 g = 2.53 and p = 0.01, g = 2.44), but no differences were observed between the RT and SS groups (p = 1.00). Furthermore, the RT group demonstrated a larger improvement in 50% and 95% ROM ISLDL compared to SS (p < 0.01, g = 2.69-3.36) and CON (p < 0.01, g = 2.44-2.57).

CONCLUSION

Resistance training through a full ROM was equally effective as SS for improving S&R flexibility, but improved hip- and lower back extensor strength more than SS and the CON. The authors recommend using large ROM resistance training to improve hip and lower back extensor flexibility and muscle strength.

TRIAL REGISTRATION

ISRCTN88839251, registered 24. April 2024, Retrospectively registered.

Unsupervised Machine Learning in Countermovement Jump and Isometric Mid-Thigh Pull Performance Produces Distinct Combat and Physical Fitness Clusters in Male and Female U.S. Marine Corps Recruits

INTRODUCTION

Several challenges face the U.S. Marine Corps (USMC) and other services in their efforts to design recruit training to augment warfighter mobility and resilience in both male and female recruits as part of an integrated model. Strength and power underpin many of the physical competencies required to meet the occupational demands one might face in military. As the military considers adopting force plate technology to assess indices of strength and power, an opportunity presents itself for the use of machine learning on large datasets to deduce the relevance of variables related to performance and injury risk. The primary aim of this study was to determine whether cluster analysis on baseline strength and power data derived from countermovement jump (CMJ) and isometric mid-thigh pull (IMTP) adequately partitions men and women entering recruit training into distinct performance clusters. The secondary aim of this study is then to assess the between-cluster frequencies of musculoskeletal injury (MSKI).

MATERIALS AND METHODS

Five hundred and sixty-five males (n = 386) and females (n = 179) at the Marine Corps Recruit Depots located at Parris Island and San Diego were enrolled in the study. Recruits performed CMJ and IMTP tests at the onset of training. Injury data were collected via medical chart review. Combat fitness test (CFT) and physical fitness test (PFT) results were provided to the study team by the USMC. A k-means cluster analysis was performed on CMJ relative peak power, IMTP relative peak force, and dynamic strength index. Independent sample t-tests and Cohen's d effect sizes assessed between-cluster differences in CFT and PFT performance. Differences in cumulative incidence of lower extremity %MSKIs were analyzed using Fisher's exact test. Relative risk and 95% confidence intervals (CIs) were also calculated.

RESULTS

The overall effects of cluster designation on CMJ and IMTP outcomes ranged from moderate (relative peak power: d = -0.68, 95% CI, -0.85 to -0.51) to large (relative peak force: d = -1.69, 95% CI, -1.88 to -1.49; dynamic strength index: d = 1.20, 95% CI, 1.02-1.38), indicating acceptable k-means cluster partitioning. Independent sample t-tests revealed that both men and women in cluster 2 (C2) significantly outperformed those in cluster 1 (C1) in all events of the CFT and PFT (P < .05). The overall and within-gender effect of cluster designation on both CFT and PFT performance ranged from small (d > 0.2) to moderate (d > 0.5). Men in C2, the high-performing cluster, demonstrated a significantly lower incidence of ankle MSKI (P = .04, RR = 0.2, 95% CI, 0.1-1.0). No other between-cluster differences in MSKI were statistically significant.

CONCLUSIONS

Our results indicate that strength and power metrics derived from force plate tests effectively partition USMC male and female recruits into distinct performance clusters with relevance to tactical and physical fitness using k-means clustering. These data support the potential for expanded use of force plates in assessing readiness in a cohort of men and women entering USMC recruit training. The ability to pre-emptively identify high and low performers in the CFT and PFT can aid in leadership developing frameworks for tailoring training to enhance combat and physical fitness with benchmark values of strength and power.

Neuromuscular Strength and Power Predict Musculoskeletal Injury and Attrition During Marine Corps Recruit Training

INTRODUCTION

Elevated rates of musculoskeletal injuries (MSIs) and attrition are documented in military recruit training. By identifying and addressing modifiable risk factors, the rate of successful training completion and military readiness can be enhanced. Despite their impact, the causes of MSIs and attrition among U.S. Marine Corps (USMC) recruits remain underexplored. This study investigates demographic, psychological, and physiological predictors of MSIs and attrition among USMC recruits.

MATERIALS AND METHODS

In this prospective cohort study, we evaluated USMC recruits at Marine Corps Recruit Depot, Parris Island and San Diego. Recruits were briefed and invited to volunteer. All recruits who were medically cleared to participate in recruit training were eligible to participate in the study. We gathered baseline data on potential predictors at the start of training, with follow-up data on MSIs and attrition collected post-training. Analyzed predictors encompassed dynamic and static strength measures from countermovement jumps, isometric mid-thigh pulls; and participant surveys. We employed multiple logistic regression to discern risk factors for MSI and attrition.

RESULTS

Our study comprised 584 USMC recruits (183 female recruits, 19.49 ± 1.88 years, 160.10 ± 7.17 cm, 61.19 ± 8.05 kg; 401 males, 18.94 ± 1.92 years, 172.97 ± 7.26 cm, 73.86 ± 11.04 kg). We observed 193 MSIs in 135 recruits, with 80.31% affecting the lower extremity (LE). Notably, lower relative peak power (odds ratio [OR] 0.91 [0.89, 0.94], P < .001) and shorter eccentric deceleration duration (OR 0.99 [0.99, 1.00], P = .005) were significant predictors of MSIs. Specifically, for LE MSIs, similar trends were noted for relative peak power and eccentric deceleration duration, with additional risks associated with lower body mass index (OR 0.93 [0.86, 0.99], P = .036) and previous LE MSIs (OR 2.25 [1.18, 4.27], P = .013). Attrition was more likely with a reduced eccentric deceleration impulse (OR 0.98 [0.97, 0.99], P < .001) and prolonged time to peak force (OR 1.36 [1.17, 1.59], P < .001) and cigarette use (OR 2.12 [1.01, 4.43], P = .046).

CONCLUSIONS

MSIs and attrition during USMC recruit training significantly undermine force readiness and escalate costs. Our research has pinpointed several modifiable risk factors, chiefly reduced muscular power and cigarette smoking. We advocate for neuromuscular training programs to bolster strength and power, integrated nutrition and exercise strategies for optimal body composition, and support for smoking cessation to alleviate the incidence of MSIs and curtail attrition. Initiating training with a gradual increase in activity intensity can provide a critical window to correct pre-existing neuromuscular imbalances and weaknesses, particularly those stemming from prior MSIs. Effectively addressing these risk factors is pivotal for diminishing the rates of MSIs and attrition among recruits, thereby enhancing overall military readiness and operational efficiency.

A Sex Comparison of the Physical and Physiological Demands of United States Marine Corps Recruit Training

INTRODUCTION

The U.S. Marine Corps (USMC) recruit training is a 13-week preparatory period for military service men and women. Differences in absolute performance capabilities between sexes may impact physical and physiological responses to the demands of recruit training. The purpose of this study was to monitor U.S. Marine Corps recruits throughout recruit training to comparatively assess workload, sleep, stress, and performance responses in men and women.

MATERIALS AND METHODS

A total of 281 recruits (men = 182 and women = 99; age = 19 ± 2 years) were monitored and tested. Workload, sleep, and stress assessments occurred at week 2, week 7/8, and week 11 of training. Workload (energy expenditure per kg body mass [EEREL], distance [DIS], steps) and sleep (continuity and duration) were tracked over 72-hour periods using wearable accelerometry and heart rate technology. Stress responses were determined through salivary cortisol analyses. Performance testing, consisting of countermovement vertical jump (CMJ) and isometric mid-thigh pull (IMTP) performance relative to body mass, occurred at weeks 2 and 11. Linear mixed models were used to test for sex, time, and sex-by-time interactions (α < .05).

RESULTS

On average, recruits covered 13.0 ± 2.7 km/day, expended 3,762 ± 765 calories/day, and slept 6.2 ± 1.1 hours/night. Sex-by-time interactions were found for DIS, steps, sleep duration, cortisol, and CMJREL performance (P < .05). Planned contrasts revealed that men covered more DIS than women at week 7/8 (P < .001). Women experienced greater step counts compared to men at week 11 (P = .004). Women experienced no significant change in sleep duration (P > .05), whereas men increased sleep duration from week 2 to week 7/8 (P = .03). Women experienced greater sleep duration at week 2 (P = .03) and week 11 (P = .02) compared to men. Women exhibited higher cortisol levels than men at week 2 (P < .001) and week 11 (P < .001). Women experienced declines in cortisol at week 7 compared to week 2 (P < .001). Men experienced no changes in cortisol response at any timepoint (P > .05). Both sexes experienced declines in CMJREL from week 2 to week 11 (P > .001). Sex main effects were observed for EEREL, DIS, CMJREL, and IMTPREL (P < .05) with men experiencing greater overall workloads and producing greater strength and power metrics. Sex main effects were also found for sleep continuity and cortisol (P < .05), for which men experienced lower values compared to women. Time main effects were observed for EEREL, DIS, steps, cortisol, CMJREL, and IMTPREL (P < .05).

CONCLUSIONS

This study not only highlights the known sex differences between men and women but also sheds light on the different physical and physiological responses of each sex to military training. Interestingly, the greatest physical demands incurred earlier in the training cycle. Despite declining workloads, the stress response was maintained throughout the training, which may have implications for adaptation and performance. In addition, average sleep duration fell notably below recommendations for optimizing health and recovery. Effectively monitoring the demands and performance outcomes during recruit training is essential for determining individual fitness capabilities, as well as establishing the effectiveness of a training program. Individual performance assessments and adequately periodized workloads may help to optimize recruit training for both men and women.

Design Considerations for a Multidisciplinary Approach to Provide Policy Recommendations on Gender-Integrated Recruit Training in the Marine Corps

INTRODUCTION

Recruit training is designed to transform civilians into physically fit military service members, who embody their service's core values and possess military discipline and skills. At the time this research began, the U.S. Marine Corps (USMC) remained the only service that segregated recruits by gender at the lowest unit level (e.g., platoon) and employed gender-segregated drill instructor teams. USMC's Marine Corps Recruit Depots (MCRD) must comply with a 2020 Congressional Mandate to not segregate training by gender in Parris Island by 2025 and San Diego by 2028. In turn, USMC requested an independent scientific study to analyze current approaches to gender integration at recruit training to propose alternate models and other policy recommendations that increase gender integration while maintaining current USMC standards. The Marine Corps is currently evaluating alternate models and recommendations to optimize entry-level training. This article outlines considerations for choosing the optimal research study design, research methods, and types of data collected in a study intended to provide policy recommendations on gender-integrated recruit training for the USMC.

MATERIALS AND METHODS

Research data were collected during visits to the MCRDs and selected recruit training locations for the Army, Air Force, Navy, and Coast Guard. Data collection on USMC recruits from three cohorts involved social science assessments (focus groups and surveys) and human performance testing (countermovement jumps and isometric mid-thigh pulls, sleep and activity wearables, and cortisol data) at multiple points in the training cycle. Data on recruits from the sister services were limited to social science assessments. Approximately 600 recruits between the two MCRDs and 160 recruits from the sister services participated in the study during a 7-month timeframe in 2021. The research team conducted extensive ethnographic observations of recruit training at all selected research sites and interviewed training cadre, drill instructors, and service leadership responsible for recruit training (∼90 interviews). Additionally, the research team interviewed 20 experts on gender integration or recruit training who possessed alternate viewpoints from the current USMC practice.

RESULTS

The mixed methods study was designed to assess the current gender integration practices at recruit training across the services to generate alternative models of gender integration for USMC. The research team developed a set of multidisciplinary objectives and research questions serving as the foundation of the research study design and data collection process. The study was designed to collect qualitative, quantitative, and administrative data informed by social science and human performance disciplines. To ensure that all aspects and implications relevant to gender integration were considered, select data were collected across services and with stakeholders at all levels.

CONCLUSIONS

This multidisciplinary research approach provided a comprehensive picture of the current USMC recruit training models. The research team captured multiple perspectives and data points for analysis through an expansive view on gender integration across all services, by interacting with participants at all levels of the institutions in varied ways. The information and data gathered enabled the research team to establish objective, data-driven alternate models, and recommendations for enhancing gender integration at recruit training for the USMC.

The dynamic strength index is a reliable and feasible tool to assess neuromuscular performance in male and female handball players

The aim of this study was to explore the reliability and feasibility of the isometric mid-thigh pull (IMTP) and dynamic strength index (DSI) in semi-professional handball players (seventeen male and eighteen female). A cross-sectional design was used to determine the test-retest reliability of several kinetic metrics registered with a force plates. The peak force, peak relative force, rate of force development (RFD 0-250 ms), and impulse 0-250 ms were selected from the IMTP test, whereas the peak propulsive force was chosen from the countermovement jump test to obtain the DSI. The intraclass correlation coefficient (ICC), coefficient of variation (CV), standard error of the measurement (SEM) and smallest detectable difference (SDD) were calculated. A paired sample t-test was also performed. No significant differences were found between the testing sessions for all variables, except for peak propulsive force for all players (p = 0.036) and DSI for female players (p = 0.037). Reliability for all kinetic metrics was good to excellent (ICC = 0.78-0.97), with low variability (CV ≤ 8.64%), being the SEM scores lower than SDD. In conclusion, the IMTP test and DSI are highly reliable and feasible tools for assessing neuromuscular performance in semi-professional handball players.

The 300 Marines: characterizing the US Marines with perfect scores on their physical and combat fitness tests

Few US Marines earn perfect 300 scores on both their Physical Fitness Test (PFT) and Combat Fitness Test (CFT). The number 300 invokes the legendary 300 Spartans that fought at the Battle of Thermopylae, which inspired high physical fitness capabilities for elite ground forces ever since.

Purpose

Determine distinguishing characteristics of the "300 Marines" (perfect PFT and CFT scores) that may provide insights into the physical and physiological requirements associated with this capability. These tests have been refined over time to reflect physical capabilities associated with Marine Corps basic rifleman performance.

Materials and methods

Data were analyzed from US Marines, including 497 women (age, 29 ± 7 years; height 1.63 ± 0.07 m; body mass, 67.4 ± 8.4 kg) and 1,224 men (30 ± 8 years; 1.77 ± 0.07 m; 86.1 ± 11.1 kg). Marines were grouped by whether they earned perfect 300 scores on both the PFT and CFT (300 Marines) or not. We analyzed group differences in individual fitness test events and body composition (dual-energy x-ray absorptiometry).

Results

Only 2.5% (n = 43) of this sample earned perfect PFT and CFT scores (n = 21 women; n = 22 men). Compared to sex-matched peers, 300 Marines performed more pull-ups, with faster three-mile run, maneuver-under-fire, and movement-to-contact times (each p < 0.001); 300 Marines of both sexes had lower fat mass, body mass index, and percent body fat (each p < 0.001). The lower percent body fat was explained by greater lean mass (p = 0.041) but similar body mass (p = 0.085) in women, whereas men had similar lean mass (p = 0.618), but lower total body mass (p = 0.025).

Conclusion

Marines earning perfect PFT and CFT scores are most distinguished from their peers by their maneuverability, suggesting speed and agility capabilities. While both sexes had considerably lower percent body fat than their peers, 300 Marine women were relatively more muscular while men were lighter.

The Effect of Palmitoylethanolamide (PEA) on Skeletal Muscle Hypertrophy, Strength, and Power in Response to Resistance Training in Healthy Active Adults: A Double-Blind Randomized Control Trial

BACKGROUND

Palmitoylethanolamide (PEA) has analgesic/anti-inflammatory properties that may be a suitable alternative to over-the-counter (OTC) non-steroidal analgesics/anti-inflammatories. While OTC pain medications can impair strength training adaptations, the mechanism of action of PEA is distinct from these and it may not negatively affect skeletal muscle adaptations to strength training.

METHODS

The primary aim of this study was to investigate the effects of daily PEA supplementation (350 mg Levagen + equivalent to 300 mg PEA) combined with 8-weeks of resistance training on lean body mass with secondary aims addressing strength, power, sleep, and wellbeing compared to placebo (PLA) in young, healthy, active adults. In a randomized, controlled, double-blinded trial, 52 untrained, recreationally active participants aged 18-35 y were allocated to either the PEA or PLA groups. Participants consumed either 2 × 175 mg Levagen + PEA or identically matched maltodextrin capsules during an 8-week period of whole-body resistance training. This trial assessed the pre- to post- changes in total and regional lean body mass, muscular strength (1-RM bench, isometric mid-thigh pull), muscular power [countermovement jump (CMJ), bench throw], pain associated with exercise training, sleep, and wellbeing compared with the PEA or PLA condition.

RESULTS

48 Participants were included in the final intention to treat (ITT) analysis and we also conducted per protocol (PP) analysis (n = 42). There were no significant between-group differences for total or regional lean muscle mass post-intervention. There was a significantly higher jump height (CMJ) at week 10 in the PEA group compared to the PLA (Adjusted mean difference [95% CI] p-value; ITT: - 2.94 cm [- 5.15, - 0.74] p = 0.010; PP: - 2.93 cm [- 5.31, - 0.55] p = 0.017). The PLA group had higher 1-RM bench press post-intervention compared with the PEA group (ITT: 2.24 kg [0.12, 4.37] p = 0.039; PP: 2.73 kg [0.40, 5.06] p = 0.023). No significant treatment effects were noted for any of the other outcomes.

CONCLUSION

PEA supplementation, when combined with 8 weeks of strength training, did not impair lean mass gains and it resulted in significantly higher dynamic lower-body power when compared with the PLA condition.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry (ANZCTR: ACTRN12621001726842p).

The Strength Characteristics of Elite and Subelite Female Gaelic Football Players

ABSTRACT

Hughes, W, Healy, R, Lyons, M, Higginbotham, C, Lane, A, and Beattie, K. The strength characteristics of elite and subelite female Gaelic football players. J Strength Cond Res 38(6): 1072-1081, 2024-There is currently an underrepresentation of sports science research focused on the female athlete, specifically in the context of Gaelic football. The aims of this study are to (a) compare the strength characteristics of elite and subelite players and (b) establish normative-based values and percentile scores for the strength characteristics of female Gaelic football players. Ninety-two female Gaelic football players were recruited for this study and subsequently categorized as elite (intercounty n = 30, age; 25.1 ± 5.3 years, stature; 1.69 ± 0.06 m, mass; 69.5 ± 5.9 kg) or subelite (club n = 62, age; 25.4 ± 6.8 years, stature; 1.66 ± 0.06 m, mass; 65.1 ± 8.9 kg). The physical strength characteristics of the subjects were assessed through the isometric midthigh pull (IMTP), countermovement jump (CMJ), and 10-5 repeated jump test. Statistically significant differences were found in the physical strength characteristics between the groups with elite players demonstrating greater peak force (large effect), relative peak force (moderate effect), and reactive strength index (large effect). Statistically significant differences were also observed for key CMJ phase characteristics with elite players producing greater RSI mod (moderate effect), jump height (large effect), and propulsion peak power (large effect) than subelite players. This study demonstrated that there are moderate to large differences between playing standards with elite players displaying superior reactive-, explosive-, and maximal-strength than their subelite counterparts. The strength characteristics evaluated in this study may be used in conjunction with other performance indices to distinguish between elite and subelite playing standards in female Gaelic football players.

Relationships and Within-Group Differences in Physical Attributes and Golf Performance in Elite Amateur Female Players

The aim of the present study was to examine the association between a comprehensive physical testing battery and measures of golf performance in elite female amateur players. Nineteen category one (handicap ≤ 5) or better golfers (age: 16.26 ± 1.28 years, height: 166.26 ± 3.62 cm, mass: 64.04 ± 11.27 kg, wingspan: 146.53 ± 15.59 cm, handicap: +1.45 ± 0.7) volunteered to participate in this investigation. All golfers attended a single 90 min testing session where golf shot data (clubhead speed [CHS], ball speed, carry distance, and smash factor) were measured with a Trackman 4 launch monitor and a battery of physical assessments were carried out. These included anthropometric data and assessments for seated thoracic rotation, the isometric mid-thigh pull (IMTP), isometric bench press, countermovement jump (CMJ), and seated medicine ball throws for distance. Pearson's r correlations showed CHS was the golf metric that most commonly demonstrated large associations with physical testing data, most notably with force at 100 ms during the isometric bench press (r = 0.70). Median split analysis was also conducted for the IMTP (force at 200 ms), isometric bench press (force at 100 ms), and CMJ (positive impulse). The results showed that players who produced more force at 200 ms during the IMTP exhibited a greater CHS (g = 1.13), ball speed (g = 0.90), and carry distance (g = 1.01). In addition, players with a greater positive impulse during the CMJ showed a greater ball speed (g = 0.93), carry distance (g = 1.29), and smash factor (g = 1.27). Collectively, these results highlight the relevance of explosive force production capabilities in both the lower and upper body for female golfers. This information can be used by practitioners to better target key physical attributes during testing and training of female players.

Anthropometric and physiological profiles of highly trained sailors in various positions and levels

This study aimed to analyze anthropometric and physiological profiles of highly trained sailors and the differences between sailors regarding various training levels. Forty-two sailors (22 male, 22.4 ± 3.8 years; 20 females, 21.3 ± 3.6 years) were divided into helmsmen and crew groups, and the high- and low-level were distinguished. Sailors completed height, sitting height, legs length, weight, BMI, VO2max, 30 s all-out sprint, isometric mid-thigh pull (IMTP), countermovement jump, bench pull, core endurance tests. The results showed the crew had higher height, sitting height, weight, VO2max and lower trunk flexor endurance test times compared to the helmsmen (p < 0.05). The helmsmen had higher relative peak power/force in the 30 s all-out sprint and IMTP tests compared to the crew, whereas the crew had better absolute strength in bench pull, with significant differences between female sailors (p < 0.05). The high-level sailors showed more sailing experience than low-level sailors (p < 0.05). In conclusion, highly trained crew tend to be taller and heavier, while helmsmen have better trunk flexor endurance. For female sailors, helmsmen have better lower-body power and strength and crew have better upper-body strength. Sailing experience is a reliable variable to distinguish sailors' levels. The specific anthropometric and physiological profiles of sailors in various positions can assist sailing coaches in athlete selection and intervention training.

Longitudinal changes in anthropometric, physiological, and physical qualities of international women's rugby league players

This is the first study to assess longitudinal changes in anthropometric, physiological, and physical qualities of international women's rugby league players. Thirteen forwards and 11 backs were tested three times over a 10-month period. Assessments included: standing height and body mass, body composition measured by dual x-ray absorptiometry (DXA), a blood panel, resting metabolic rate (RMR) assessed by indirect calorimetry, aerobic capacity (i.e.,[Formula: see text]) evaluated by an incremental treadmill test, and isometric force production measured by a force plate. During the pre-season phase, lean mass increased significantly by ~2% for backs (testing point 1: 47 kg; testing point 2: 48 kg) and forwards (testing point 1: 50 kg; testing point 2: 51 kg) (p = ≤ 0.05). Backs significantly increased their [Formula: see text] by 22% from testing point 1 (40 ml kg-1 min-1) to testing point 3 (49 ml kg-1 min-1) (p = ≤ 0.04). The [Formula: see text] of forwards increased by 10% from testing point 1 (41 ml kg-1 min-1) to testing point 3 (45 ml kg-1 min-1), however this change was not significant (p = ≥ 0.05). Body mass (values represent the range of means across the three testing points) (backs: 68 kg; forwards: 77-78 kg), fat mass percentage (backs: 25-26%; forwards: 30-31%), resting metabolic rate (backs: 7 MJ day-1; forwards: 7 MJ day-1), isometric mid-thigh pull (backs: 2106-2180 N; forwards: 2155-2241 N), isometric bench press (backs: 799-822 N; forwards: 999-1024 N), isometric prone row (backs: 625-628 N; forwards: 667-678 N) and bloods (backs: ferritin 21-29 ug/L, haemoglobin 137-140 g/L, iron 17-21 umol/L, transferrin 3 g/L, transferring saturation 23-28%; forwards: ferritin 31-33 ug/L, haemoglobin 141-145 g/L, iron 20-23 umol/L, transferrin 3 g/L, transferrin saturation 26-31%) did not change (p = ≥ 0.05). This study provides novel longitudinal data which can be used to better prepare women rugby league players for the unique demands of their sport, underpinning female athlete health.

A survey into the current fitness testing practices of elite male soccer practitioners: from assessment to communicating results

This study provides insight into the current fitness testing practices in elite male soccer. One hundred and two practitioners from professional soccer leagues across 24 countries completed an online survey comprising 29 questions, with five sections: a) background information, b) testing selection, c) testing implementation, d) data analysis, and e) data reporting. Frequency analysis was used to evaluate the responses to fixed response questions and thematic analysis was used for open-ended questions to generate clear and distinct themes. Strength (85%) and aerobic capacity (82%) represent the most frequently assessed physical qualities. Scientific literature (80%) is the most influential factor in testing selection and practitioners conduct fitness testing less frequently than their perceived ideal frequency per season (3.6 ± 2 vs. 4.5 ± 2). Time and competitive schedule were the greatest barriers to fitness testing administration. Practitioners mostly used a 'hybrid' approach (45%) to fitness testing, blending 'traditional' (i.e., a day dedicated to testing) and 'integrated' (i.e., testing within regular training sessions) methods. Microsoft Excel is the most used software for data analysis (95%) and visualization (79%). An equal use of the combination of best and mean scores of multiple trials (44%) and the best score (42%) was reported. Comparing a player's test performance with previous scores (89%) was the most common method for interpreting test results. However, only 38% considered measurement error. Digital displays and verbal feedback are the most common data reporting methods, with different data reporting processes for coaches and players. Practitioners can use data and findings from this study to inform their current testing practices and researchers to further identify areas for investigation, with the overarching aim of developing the field of fitness testing in elite male soccer.

Relative strength explains the differences in multi-joint rapid force production between sexes

The primary aim of this study was to determine whether relative strength explains the differences in the rapid force production (force developed during first 150-, 200-, and 250 ms) of females and males, and to evaluate the relationships between peak force and rapid force production. Sixty-three team sport athletes (females: n = 25, age = 21.5 ± 1.3 years, stature = 166 ± 5 cm, body mass = 60.65 ± 10.04 kg; males: n = 38, age = 21.9 ± 1.1 years, stature = 178 ± 7 cm, body mass = 76.55 ± 12.88 kg) performed a series of isometric mid-thigh pull (IMTP) trials, with all participants' data used for correlational analysis. After testing, females and males were divided into 20 strength-matched pairs, based on their relative peak force (peak force ∙ body mass). There were no meaningful differences between sexes for relative force at 150 ms (g = 0.007 [95% CI -0.627, 0.648]), 200 ms (g = -0.059 [95% CI -0.695, 0.588]) and 250 ms (g = -0.156 [95% CI -0.778, 0.473]). Similarly, when expressed as a percentage of peak force there were no meaningful differences in force at 150 ms (g = -0.015 [95.0%CI -0.650, 0.680]), 200 ms (g = -0.099 [95.0%CI -0.714, 0.559]) or 250 ms (g = -0.272 [95.0%CI -0.856, 0.328]) between strength-matched females and males. Based on the correlations, there were very large to nearly perfect relationships (r = 0.77-0.94, p <0.001) between peak force and rapid force production, with peak force explaining 59%, 77% and 89% of the variance in force at 150-, 200- and 250 ms, respectively. When comparing females and males, relative strength (based on body weight or a percentage of peak force) should be considered, and practitioners should be aware of the role of peak force in rapid force production.

The Relationship Between Isometric Midthigh Pull Force-Time Characteristics and 2-km Load-Carrying Performance in Trained British Army Soldiers

ABSTRACT

Nevin, JP, Bowling, K, Cousens, C, Bambrough, R, and Ramsdale, M. The relationship between isometric midthigh pull force-time characteristics and 2-km load-carrying performance in trained British army soldiers. J Strength Cond Res 38(2): 360-366, 2024-Load carriage is a fundamental military occupational task. As such, the aim of this study was to assess the relationship between isometric force-time characteristics and loaded march performance. Furthermore, this study aimed to investigate the relationship between isometric force-time characteristics and standing long jump (SLJ) performance. Thirty-nine, full-trained, male British Army infantry soldiers (age 31 ± 6.1 years; height 176 ± 7.3 cm; body mass 85.8 ± 11.5 kg) performed three isometric midthigh pull trials, three SLJ trials, and a 2-km loaded march carrying an external load of 25 kg. Both the isometric midthigh pull test (intraclass correlation coefficient [ICC] 0.965) and SLJ (ICC 0.916) demonstrated excellent reliability. Relationships between all variables were assessed using Pearson's correlation coefficient. Isometric peak force (r = -0.059), relative peak force (r = -0.135), and rate of force development (r = -0.162) displayed a small correlation with loaded march time to completion. However, isometric relative peak force displayed a large relationship with SLJ performance (r = 0.545; p = <0.01). Our data demonstrate that isometric lower-limb strength measures account for <2% of the total variance observed in 2-km loaded march performance. As such, the use of isometric lower-limb force-time characteristics as a proxy measure of load-carrying ability should be questioned. However, relative isometric strength seems to demonstrate a significant relationship with SLJ performance. As such, isometric testing may have utility in regard to assessing explosive strength, monitoring neuromuscular fatigue, and assessing training readiness in military populations.

Kinetic Analysis, Potentiation, and Fatigue During Vertical and Horizontal Plyometric Training: An In-Depth Investigation Into Session Volume

Despite previous support for plyometric training, optimal dosing strategies remain unclear.

PURPOSE

To investigate vertical and horizontal jump kinetic performance following a low-volume plyometric stimulus with progressively increased session jump volume.

METHODS

Sixteen academy rugby players (20.0 [2.0] y; 103.0 [17.6] kg; 184.3 [5.5] cm) volunteered for this study. Vertical and horizontal jump sessions were conducted 1 week apart and consisted of a 40-jump low-volume plyometric stimulus using 4 exercises, after which volume was progressively increased to 200 jumps, using countermovement jump (CMJ) for vertical sessions and horizontal broad jump (HBJ) for horizontal sessions. Jump performance was assessed via force-plate analysis at baseline (PRE-0), following the low-volume plyometric stimulus (P-40), and every subsequent 10 jumps until the end of the session (P-50, P-60, P-70, ... P-200).

RESULTS

The low-volume stimulus was effective in potentiating HBJ (2% to 5%) but not CMJ (0% to -7%) performance (P < .001). The HBJ performance enhancements were maintained throughout the entire high-volume session, while CMJ realized small but significant decrements (-5% to -7%) in jump height P-50 to P-80 before recovering to presession values. Moreover, increases in eccentric impulse (5% to 24%; P < .001) in both sessions were associated with decreased or maintained concentric impulse, indicating a breakdown in performance-augmenting mechanisms and less effective power transfer concentrically after moderate volumes.

CONCLUSION

Practitioners should consider kinetic differences between HBJ and CMJ with increasing volume to better inform and understand session dosing strategies.

Predicting repeat power ability through common field assessments: is repeat power ability a unique physical quality?

Background

The repeat power ability (RPA) assessment is used to test the ability to repeatedly produce maximal ballistic efforts with an external load. The underpinning physical qualities influencing RPA are undetermined. This study aimed to gain further insight into the physical qualities that determine RPA by analysing the association between physical qualities and an assessment of RPA.

Materials and methods

Ten well-trained male field hockey players performed an RPA assessment consisting of 20 repetitions of loaded countermovement jumps (LCMJ20), with a percent decrement score of peak power output calculated. Over a two-week period, each participant performed the YoYo Intermittent Recovery Test 2 (IRT2), a repeated speed ability assessment incorporating a 180° change of direction (RSA180), a 40-meter linear speed test (40 mST), an isometric mid-thigh pull (IMTP), a countermovement jump (CMJ), and a 3-repetition maximum half squat (HS) assessment. Pearson's correlation analysis was used to determine the strength of relationships between each assessment variable and the LCMJ20. The assessment variables with the strongest relationships within each assessment were used in a stepwise multiple linear regression analysis to determine the best predictor model of LCMJ20.

Results

RSA180percent decrement score (RSA180% had a very strong, significant relationship with LCMJ20 (r = 0.736: p < 0.05). HS relative strength (HSrel) was found to have a significant and very strong, negative relationship with LCMJ20 (r =  - 0.728: p < 0.05). Stepwise multiple linear regression analysis showed RSA180 to explain 48.4% of LCMJ20 variance (Adjusted R2 = 0.484) as the only covariate included in the model.

Conclusion

The findings indicate that RSA180 as a repeated high intensity effort (RHIE) task is strongly related to LCMJ20 and is also the best predictor of LCMJ20. This may suggest that RPA can provide practitioners with information on RHIE performance. The variance between assessment methods indicates that RPA may be a distinct physical quality, future research should assess other physical capacities to better understand the factors contributing to RPA.

A single dose multi-ingredient pre-workout supplement enhances upper body resistance exercise performance

Introduction

Multi-ingredient pre-workout supplements (MIPS) are commonly used by individuals looking to enhance exercise performance and augment adaptations to training. However, the efficacy of commercially available MIPS is largely dependent on the ingredient profile, and new formulations should be investigated to determine their effectiveness. Therefore, the purpose of this study was to examine the effects of a commercially available MIPS product on performance during an upper body resistance exercise protocol.

Methods

Twenty resistance-trained participants (10 men, 10 women) volunteered to complete this double-blind, placebo-controlled, crossover study consisting of 3 visits. Visit 1 consisted of body composition, 1-repetition maximum (1RM) testing, and familiarization. Visits 2 and 3 consisted of supplementation with either MIPS or placebo (PLA) 1 h prior to completion of an upper body resistance exercise workout during which power output, repetitions completed, rating of perceived exertion (RPE), and perceived recovery were recorded. Assessments of reaction time, isometric mid-thigh pull, and perceived levels of focus, energy, fatigue, and "muscle pump" were also completed before supplementation, 1 h after supplementation, and immediately after exercise.

Results

Statistical analysis revealed significant main effects of trial for reaction time (p < 0.001) and bench press peak power (p = 0.026) indicating better performance during the MIPS trial. Furthermore, total number of repetitions completed significantly increased (p = 0.003) during the MIPS (96.90 ± 21.31 repetitions) trial compared to PLA (89.50 ± 18.37 repetitions). Additionally, overall session RPE was significantly lower (p = 0.002) during the MIPS (7.6 ± 1.2) trial compared to PLA (8.3 ± 0.9).

Discussion

These findings suggest that acute supplementation with this MIPS improved upper body resistance exercise performance while reducing participant RPE. Further research should investigate the efficacy of chronic supplementation with this MIPS as the acute response provided an ergogenic benefit.

Training stress, neuromuscular fatigue and well-being in volleyball: a systematic review

BACKGROUND

Volleyball, with its unique calendar structure, presents distinct challenges in training and competition scheduling. Like many team sports, volleyball features an unconventional schedule with brief off-season and pre-season phases, juxtaposed against an extensive in-season phase characterized by a high density of matches and training. This compact calendar necessitates careful management of training loads and recovery periods. The effectiveness of this management is a critical factor, influencing the overall performance and success of volleyball teams. In this review, we explore the associations between training stress measures, fatigue, and well-being assessments within this context, to better inform future research and practice.

METHODS

A systematic literature search was conducted in databases including PsycINFO, MEDLINE/PubMed, SPORTDiscus, Web of Science, and Scopus. Inclusion criteria were original research papers published in peer-reviewed journals involving volleyball athletes.

RESULTS

Of the 2535 studies identified, 31 were thoroughly analysed. From these 31 articles, 22 included professional athletes, seven included collegiate-level volleyball athletes, and two included young athletes. Nine studies had female volleyball players, while the remaining 22 had male volleyball athletes.

CONCLUSIONS

Internal training load should be collected daily after training sessions and matches with the session rating of perceived exertion method. External training load should also be measured daily according to the methods based on jump height, jump count, and kinetic energy. If force platforms are available, neuromuscular fatigue can be assessed weekly using the FT:CT ratio of a countermovement jump or, in cases where force platforms are not available, the average jump height can also be used. Finally, the Hooper Index has been shown to be a measure of overall wellness, fatigue, stress, muscle soreness, mood, and sleep quality in volleyball when used daily.

Countermovement Jump Force-Time Curve Analyses: Reliability and Comparability Across Force Plate Systems

ABSTRACT

Merrigan, JJ, Strang, A, Eckerle, J, Mackowski, N, Hierholzer, K, Ray, NT, Smith, R, Hagen, JA, and Briggs, RA. Countermovement jump force-time curve analyses: reliability and comparability across force plate systems. J Strength Cond Res 38(1): 30-37, 2024-Considering the growing prevalence of commercial force plates providing automated force-time analyses, understanding levels of agreement across force plate systems is warranted. Countermovement jump (CMJ) metrics across Vald ForceDecks (FD), Hawkin Dynamics (HD), and Sparta Science (SS) force plate systems were compared. Twenty-two subjects completed CMJ testing (∼128 comparisons) on each force plate system separately with rest between jumps. Baseline testing occurred 3 times and demonstrated poor test-retest reliability for modified reactive strength index (mRSI) and rate of force development (RFD). ForceDecks and HD comparisons yielded acceptable agreement for concentric/propulsive relative force and net impulse, jump height, eccentric/braking RFD, and mRSI, but systematic and proportionate bias existed for RFD. Sparta Science jump height and reactive strength index (RSI) demonstrated systematic overestimations compared with HD and FD, but jump height had acceptable agreement according to concordance correlation coefficients (CCC = 0.92-0.95). Agreement between SS load (eccentric RFD) and HD braking RFD was acceptable (CCC = 0.91), whereas agreement between SS load and FD deceleration RFD was considered acceptable (CCC = 0.81-0.87) but demonstrated systematic and proportionate bias. ForceDecks (CCC = 0.89) and HD (CCC = 0.85) average relative concentric/propulsive force yielded acceptable agreement with SS explode (average relative concentric force), but SS explode demonstrated systematically lower values than FD and HD. Sparta Science drive (concentric impulse) yielded acceptable agreement with HD relative propulsive impulse (CCC = 0.85), but not FD concentric impulse. Human performance practitioners need to be aware of inconsistencies among testing procedures and analyses across force plate systems, such as differences in metric definitions and units of measurement, before making comparisons across systems.

Validity and Reliability of Force-Time Characteristics Using a Portable Load Cell for the Isometric Midthigh Pull

ABSTRACT

Pichardo, AW, Neville, J, Tinwala, F, Cronin, JB, and Brown, SR. Validity and reliability of force-time characteristics using a portable load cell for the isometric midthigh pull. J Strength Cond Res 38(1): 185-191, 2024-Many practitioners use the isometric midthigh pull (IMTP) to assess maximal strength in a safe, time-effective manner. However, expensive, stationary force plates are not always practical in a large team setting. Therefore, the purpose of this study was to establish the validity and between-session reliability of peak force, rate of force development (RFD), and impulse during an IMTP using 2 experimental protocols: a traditional fixed bar with a force plate (BarFP) and a flexible chain measured with a force plate (ChainFP) and a load cell (ChainLC). After a familiarization session, 13 resistance-trained men performed 3 trials of the BarFP condition and 3 trials of the chain-based conditions. The identical procedures were replicated twice more, with a week between each testing session. The main findings were (a) no RFD or impulse measures were found to achieve acceptable reliability across all methodological approaches and testing occasions; (b) peak force was reliable across all methods, with coefficient of variation ranging from 4.6 to 8.3%, intraclass correlation coefficient ranging from 0.94 to 0.98, and the least variability associated with the ChainLC condition; and (c) the ChainFP method was found to significantly underrepresent peak force by 4.8% (p < 0.05), with no significant differences between the ChainLC and BarFP methods. Therefore, the ChainLC would seem a valid, reliable, portable, and cost-effective alternative to force plates when assessing maximal isometric strength in the IMTP.

The Effects of Low-Load Squat Jump and Maximal Isometric Priming Exercise on Muscular Performance and Perceptual State

ABSTRACT

Harrison, PW, James, LP, Jenkins, DG, McGuigan, MR, Holmberg, PM, and Kelly, VG. The effects of low-load squat jump and maximal isometric priming exercise on muscular performance and perceptual state. J Strength Cond Res 38(1): 1-9, 2024-The aim of this study was to examine responses at 3 and 27 hours after low-load jump squat (LL) and maximal isometric half-squat (ISO) priming stimuli. Fifteen resistance-trained males performed LL (4 × 3 at 20% 1 repetition maximum [1RM]), ISO (4 × 3 seconds), and control (CON) activities (standardized warm-up) in a randomized and counterbalanced order. Countermovement jump (CMJ) and isometric midthigh pull tests were conducted to assess performance changes after priming and CON activities. No clear changes in CMJ measures were found after priming activities compared with CON. However, small effect size improvements were found after priming stimuli completed on the same day. A 2.9% decrease in concentric phase duration (CI = 0.3-5.9, p = 0.333, Cliff's delta = -0.156) and a 9.1% increase in RSImod (CI = 0.2-12.3, p = 0.151, Cliff's delta = -0.218) occurred at 3 hours after LL compared with CON. Braking phase duration (CI = 0.8-10.6, p = 0.333, Cliff's delta = -0.213) was 2.9% shorter at 3 hours after ISO compared with CON. No clear changes in isometric peak force occurred after priming activities compared with CON. Additionally, questionnaires were completed to assess perceptual state and perceived effectiveness of the priming stimulus to influence performance. An increase in the "effect of activity" was perceived at 3 hours after LL and ISO (p = 0.013-0.044, Cliff's delta = 0.578-0.6) and at 27 hours after ISO (p = 0.99, Cliff's delta = 0.173) compared with CON. An increase in "muscular heaviness" was also reported at 3 hours after ISO compared with CON (p = 0.199, Cliff's delta = 0.320). The collective findings suggest limited benefits over the day after LL and ISO priming stimuli. However, as there was substantial variation in individual responses, the relative nature of priming responses should be considered when prescribing similar strategies in practical environments.

Dynamic and Isometric Force-Time Curve Characteristics Influencing Change of Direction Performance of State-Level Netball Players

ABSTRACT

Smolarek, T, Haff, GG, Poon, WCK, Nagatani, T, Barley, OR, and Guppy, SN. Dynamic and isometric force-time curve characteristics influencing change of direction performance of state-level netball players. J Strength Cond Res 37(12): 2397-2404, 2023-Although multiple lower-body strength capacities are required to change direction rapidly, there is limited knowledge about the relative importance of these factors. Therefore, the purpose of this study was to assess the relationship between dynamic and isometric lower-body strength capacities and change of direction (COD) time in state-league netball players. Seventeen female athletes completed maximal isometric midthigh pull (IMTP), countermovement jump (CMJ), and modified 5-0-5 COD tests. Pearson's product moment correlations were used to determine the relationship between COD time and several IMTP and CMJ force-time curve characteristics. To assess the level of contribution of each force-time curve characteristic to COD time, multivariate-linear stepwise regression analyses were performed. A significant moderate correlation was noted between net relative peak force (PF) during the IMTP and COD time ( r = 0.488, p = 0.047), accounting for 23.8% of the variance in COD time. Moreover, concentric relative impulse during the CMJ was strongly correlated with COD time ( r = 0.718; p = 0.001), explaining 81.9% of the variance in COD time when combined with net relative braking PF in a stepwise regression. Based on these findings, female netball players who display higher concentric and isometric strength, as well as the ability to express higher impulses during the concentric phase of the CMJ, are likely to perform CODs faster. This may occur because COD requires the generation of greater propulsive forces, as well as reduced braking and contact times, along with greater isometric strength enabling effective repositioning of center of mass during COD tasks.

Effect of the Intrasession Exercise Order of Flywheel Resistance and High-Intensity Interval Training on Maximal Strength and Power Performance in Elite Team-Sport Athletes

Petré, H, Ovendal, A, Westblad, N, Ten Siethoff, L, Rosdahl, H, and Psilander, N. Effect of the intrasession exercise order of flywheel resistance and high-intensity interval training on maximal strength and power performance in elite team-sport athletes. J Strength Cond Res 37(12): 2389–2396, 2023—This study aimed to investigate the effect of intrasession exercise order of maximal effort flywheel resistance training (RT; 4 × 6 repetitions [rep]) and high-intensity interval training (HIIT, 2–4 × 8 rep of 20 second at 130% of Watt at V̇o 2max [wV̇o 2max]), on the development of maximal strength and power in elite team-sport athletes. A 7-week training intervention involving 2 training sessions per week of either HIIT followed by RT (HIIT + RT, n = 8), RT followed by HIIT (RT + HIIT, n = 8), or RT alone (RT, n = 7) was conducted in 23 elite male bandy players (24.7 ± 4.3 years). Power and work were continuously measured during the flywheel RT. Isometric squat strength (ISq), countermovement jump, squat jump, and V̇o 2max were measured before and after the training period. Power output during training differed between the groups (p = 0.013, η p 2 = 0.365) with RT producing more power than HIIT + RT (p = 0.005). ISq improved following RT + HIIT (∼80%, d = 2.10, p = 0.001) and following HIIT + RT (∼40%, d = 1.64, p = 0.005), and RT alone (∼70%, d = 1.67, p = 0.004). V̇o 2max increased following RT + HIIT and HIIT + RT (∼10%, d = 1.98, p = 0.001 resp. d = 2.08, p = 0.001). HIIT before RT reduced power output during RT in elite team-sport athletes but did not lead to blunted development of maximal strength or power after a 7-week training period. During longer training periods (>7-weeks), it may be advantageous to schedule RT before HIIT because the negative effect of HIIT + RT on training quality increased during the final weeks of training. In addition, the largest training effect on maximal strength was observed following RT + HIIT.

Comparison of Force Measures Between Start Position, Transition Phase, and Midthigh Pull With Weightlifting Performance During Israel National Competition

ABSTRACT

Ben-Zeev, T, Sadres, E, and Hoffman, JR. Comparison of force measures between start position, transition phase, and midthigh pull with weightlifting performance during Israel National Competition. J Strength Cond Res 37(11): 2200-2205, 2023-This study compared the relationship between peak force (PKF) and rate of force development (RFD) at isometric start position pull (ISPP), isometric transition position pull (ITPP), and isometric midthigh pull (IMTP) with the snatch (SN), clean and jerk (C&J), and total score (TOT) in 30 national and international Israeli weightlifters (18 men and 12 women). All measures were collected either 1 week before or 1 week after the Israel weightlifting championship. A significant correlation was observed between peak force at all pull positions and performance in the SN, C&J, and TOT for men, women, and both sexes combined ( p < 0.001). The correlations were all very strong (e.g., r values all above 0.90) for both ISPP and ITPP, and all weightlifting performance variables, whereas the correlation between IMTP and weightlifting performance ranged from moderate ( r = 0.69) to strong ( r = 0.89). In addition, significant differences were observed between the correlation coefficient value in ISPP and ITPP with the TOT score compared with the correlations observed in IMTP ( z = 0.7, p = 0.046, and z = 1.7, p = 0.049, respectively). Significant differences were also observed in the women group for ISPP for the SN and TOT score compared with the correlation in IMTP ( z = 1.72, p = 0.043, and z = 1.75, p = 0.040, respectively). Rate of force development at 250 milliseconds significantly ( p values <0.05) correlated with the SN, C&J, and TOT in women ( r 's = 0.65, 0.68, and 0.67, respectively), and when both sexes were combined ( r 's = 0.59, 0.61, and 0.60, respectively), but not for the men. Results of this investigation indicated the importance of isometric force capabilities at ISPP and ITPP for weightlifting performance.

Evaluation of force-time curve analysis methods in the isometric mid-thigh pull test

The purpose of this study was to evaluate the manual and automatic analysis methods for force-time curve analysis of the isometric mid-thigh pull (IMTP) test. The visual analysis, first derivative analysis and threshold analysis methods were used to analyse onset time and time-specific forces at 50 ms, 90 ms, 200 ms and 250 ms on the force-time curve. Ninety-three collegiate sports athletes' trials were selected and analysed by each method. The visual analysis method was set as the reference method for paired comparisons with the first derivative analysis method and threshold analysis method. Onset time comparisons revealed that the first derivative analysis method was comparable with the visual analysis method with average difference at about 30 ms. Results from the weighted least products regression analysis and the Bland-Altman analysis showed that large fixed bias confounded by proportional bias existed in the threshold analysis method, and time-specific force variables obtained from the first derivative analysis method were closer to those from the visual analysis method when compared with the threshold analysis method. These findings suggest that the first derivative analysis method could be an effective tool for force-time curve analysis of the IMTP test.

Force plate methodologies applied to injury profiling and rehabilitation in sport: A scoping review protocol

Musculoskeletal injuries are a common health problem among sporting populations. Such injuries come with a high financial burden to the involved organisations and can have a detrimental impact on the career attainment of injured individuals. Force plates are now a common tool available to sport and exercise science and medicine professionals to enable them to profile injury risk predisposition and modulate the rehabilitation process within sporting environments. This is because contemporary force plate technology is portable and affordable and often comes with software that enables the automatic and immediate feedback of test variables to key stakeholders. However, to our knowledge, to date, there has been no comprehensive review of the scientific literature pertaining to clinical applications of force plate technology. Therefore, this article presents a protocol and a methodological framework to perform a scoping review to identify and map the available scientific literature in which force plates have been applied to the injury profiling and rehabilitation of athletes. The specific aims of the scoping review are 1) to identify and describe the force plate tests, methodologies, and metrics used to screen for injury risk and guide the return of injured athletes to full-time training and competition, 2) to identify potential trends and/or differences by participants' age, sex, and/or level of performance in tests, methodologies, and metrics selected, and 3) to identify key gaps in the existing evidence base and new questions that should be addressed in future research. The global aim of the scoping review is to improve practitioner decision-making around force plate test and variable selection when applied to the injury prevention and rehabilitation of sporting populations.

Reliability and Validity of Different Lower-Limb Strength Tests to Determine 1RM in the Keiser A300 Leg Press

ABSTRACT

Larsen, F, Loturco, I, Sigvaldsen, E, Strand, MF, Kalhovde, JM, and Haugen, T. Reliability and validity of different lower-limb strength tests to determine 1RM in the Keiser A300 leg press. J Strength Cond Res 37(10): 1963-1968, 2023-The aim of this study was to explore the reliability and validity of different lower-limb strength tests to determine the one-repetition maximum (1RM) value in the Keiser A300 leg press. Twenty-eight recreationally active subjects performed load-velocity (L-V) relationship, 1RM, isometric midthigh pull (IMTP), and maximal repetitions to failure (MRF) tests on 3 separated sessions. Predicted 1RMs for the L-V relationship were estimated from a linear regression equation, correlating movement velocity and relative loads. The number of repetitions from the MRF tests (at loads relative to bodyweight) and peak force from the IMTP tests were used in regression equations to predict 1RM. The level of significance was set to ρ ≤ 0.05. All 1RM prediction methods were highly comparable with the traditional 1RM test, as only trivial and nonsignificant differences were observed. Furthermore, the L-V relationship was the most reliable (intraclass correlation coefficient [± 95% confidence interval] = 0.99 [0.98, 0.996]; effect size = -0.01 [-0.38, 0.36], standard error of the measurement = 6.4 kg; coefficient of variation = 3.0 [2.2-3.8]% and valid (r = 0.95 [0.89, 0.98], effect size = 0.08 [-0.29, 0.45], standard error of the estimate = 20.4 kg; coefficient of variation = 7.4 [5.5-9.3]%) when compared with direct 1RM measurements. The L-V relationship test showed a significant change score relationship (r = 0.41 [0.04, 0.68]) against the direct 1RM measurements. In conclusion, the tests used in this study cannot be used interchangeably, but they represent a good alternative in training settings where 1RM testing is not feasible.

Position-specific differences in countermovement vertical jump force-time metrics in professional male basketball players

The countermovement vertical jump (CVJ) is one of the most commonly implemented non-invasive and time-efficient testing modalities for lower-body neuromuscular performance assessment. With more practitioners having access to portable force plates, the purpose of this study was to examine position-specific differences in CVJ force-time metrics within a cohort of elite professional male basketball athletes. Twenty-eight athletes competing in top-tier European basketball leagues volunteered to participate in the present study. Following familiarization with testing procedures and a standardized warm-up protocol, each athlete performed three maximal-effort CVJ on a uni-axial force plate system with hands on the hips during the entire movement. To minimize the possible influence of fatigue, each jump trial was separated by an approximately 15-s rest interval. The mean value across three jumps was used for performance analysis purposes. The findings of the present study reveal notable position-specific differences during the eccentric phase of the CVJ, with centers having greater braking impulse, mean force, and mean power when compared to guards. However, when normalized by body mass, the observed differences during the eccentric phase of the CVJ were nonexistent. On the other hand, no significant differences in absolute mean and peak force and power were detected during the concentric phase of the CVJ. Yet, when normalized by the player's body mass, centers demonstrated inferior performance than guards for the same force-time metrics. Overall, these findings may help practitioners obtain a better insight into position-specific differences with regards to CVJ force-time characteristics as well as aid with individually tailored training regimen design.

ADAPTations to low load blood flow restriction exercise versus conventional heavier load resistance exercise in UK military personnel with persistent knee pain: protocol for the ADAPT study, a multi-centre randomized controlled trial

BACKGROUND

Muscle atrophy, muscle weakness and localised pain are commonly reported following musculoskeletal injury (MSKI). To mitigate this risk and prepare individuals to return to sport or physically demanding occupations, resistance training (RT) is considered a vital component of rehabilitation. However, to elicit adaptations in muscle strength, exercise guidelines recommend lifting loads ≥ 70% of an individual's one repetition maximum (1-RM). Unfortunately, individuals with persistent knee pain are often unable to tolerate such high loads and this may negatively impact the duration and extent of their recovery. Low load blood flow restriction (LL-BFR) is an alternative RT technique that has demonstrated improvements in muscle strength, hypertrophy, and pain in the absence of high mechanical loading. However, the effectiveness of high-frequency LL-BFR in a residential rehabilitation environment remains unclear. This study will compare the efficacy of high frequency LL-BFR to 'conventional' heavier load resistance training (HL-RT) on measures of physical function and pain in adults with persistent knee pain.

METHODS

This is a multicentre randomised controlled trial (RCT) of 150 UK service personnel (aged 18-55) admitted for a 3-week residential rehabilitation course with persistent knee pain. Participants will be randomised to receive: a) LL-BFR delivered twice daily at 20% 1-RM or b) HL-RT three-times per week at 70% 1-RM. Outcomes will be recorded at baseline (T1), course discharge (T2) and at three-months following course (T3). The primary outcome will be the lower extremity functional scale (LEFS) at T2. Secondary outcomes will include patient reported perceptions of pain, physical and occupational function and objective measures of muscle strength and neuromuscular performance. Additional biomechanical and physiological mechanisms underpinning both RT interventions will also be investigated as part of a nested mechanistic study.

DISCUSSION

LL-BFR is a rehabilitation modality that has the potential to induce positive clinical adaptations in the absence of high mechanical loads and therefore could be considered a treatment option for patients suffering significant functional deficits who are unable to tolerate heavy load RT. Consequently, results from this study will have a direct clinical application to healthcare service providers and patients involved in the rehabilitation of physically active adults suffering MSKI.

TRIAL REGISTRATION

ClinicalTrials.org reference number, NCT05719922.

Validity and reliability of upper body push and pull tests to determine one-repetition maximum

OBJECTIVES

The purpose of this study was to explore the validity and reliability of three different strength testing approaches to determine one-repetition maximum (1RM) in the bench press and prone bench pull.

METHODS

Twenty-eight recreationally active subjects (25 ± 2 years, 178 ± 8 cm, 78 ± 9 kg) were assessed for load-velocity (L-V) relationship, 1RM, maximal isometric force (MIF), and maximal repetitions to failure (MRF) in a Smith Machine on three separated sessions. Linear regression was used for L-V relationship, MIF, and MRF to predict 1RM. Level of significance was set to ρ ≤ 0.05.

RESULTS

Reliability analyses of the varying 1RM estimations revealed mean differences from 0.6 to -1.3 kg (mainly trivial effects) between test days 1 and 2, intraclass correlation coefficient was > 0.96, and coefficient of variation (CV) was in the range 2.3-8.3% for all tests. Regarding validity, all 1RM predictions exhibited a mean difference ≤ 1.3 kg (trivial), except for the L-V relationship method that underestimated the predicted 1RM by 5 kg (small) compared to the actual bench press 1RM. However, the L-V relationship method showed the least mean absolute errors. CVs were in the range 4.5-13.2%. Standard error of the estimate was in the range 3.2-9.7 kg. Change scores for all tests were significantly correlated with change scores in actual 1RM, except for MIF in the prone bench pull. Smallest deviations in 1RM predictions were observed for the L-V relationship approach.

CONCLUSIONS

All 1RM prediction methods were highly comparable to the traditional 1RM test. However, given the high variability associated with individual predictions for each method, they cannot be used interchangeably.

The difference between several neuromuscular tests for monitoring resistance-training induced fatigue

The purposes of this study were to investigate the acute effects of resistance training protocol on kinetic changes in squat jump (SJ), shortened isometric mid-thigh pull (IMTP), and isometric squat (ISQ) and to examine the relationship of dynamic maximum strength with performance changes over 48 hours in resistance-trained individuals. Participants completed performance tests at pre-, post-24 hours, and post-48 hours resistance training protocol (Baseline, Post24, and Post48). The training protocol consisted of 5 sets of 10 repetitions of back squat (BSQ) at 60% of 1 repetition maximum (1RM). SJ variables included jump height (JH), peak power (PP), and relative PP. For the IMTP and ISQ, isometric peak force (IPF), relative IPF, rate of force development at 250 milliseconds (RFD250), and impulse at 250 milliseconds (IMP250) were calculated. Significant decreases were observed from Baseline to Post24 (p = 0.023, Cohen's d_z effect size [d_z] = 1.00) and Post48 (p = 0.032, d_z = 0.94) in SJ JH. IMTP IMP250 significantly decreased from Baseline to Post48 (p = 0.046, d_z = 0.88). Significant negative correlation was found between relative 1RM BSQ and the changes from Baseline to Post48 in ISQ RFD250 (p = 0.046,r = -0.61). Acute performance decreases might remain until 48 hours after resistance training in explosive strength and impulse regardless of isometric testing type.

Acute Performance, Daily Well-Being, and Hormone Responses to Water Immersion After Resistance Exercise in Junior International and Subelite Male Volleyball Athletes

ABSTRACT

Horgan, BG, Tee, N, West, NP, Drinkwater, EJ, Halson, SL, Colomer, CME, Fonda, CJ, Tatham, J, Chapman, DW, and Haff, GG. Acute performance, daily well-being and hormone responses to water immersion after resistance exercise in junior international and subelite male volleyball athletes. J Strength Cond Res XX(X): 000-000, 2023-Athletes use postexercise hydrotherapy strategies to improve recovery and competition performance and to enhance adaptative responses to training. Using a randomized cross-over design, the acute effects of 3 postresistance exercise water immersion strategies on perceived recovery, neuromuscular performance, and hormone concentrations in junior international and subelite male volleyball athletes (n = 18) were investigated. After resistance exercise, subjects randomly completed either 15-minute passive control (CON), contrast water therapy (CWT), cold (CWI), or hot water immersion (HWI) interventions. A treatment effect occurred after HWI; reducing perceptions of fatigue (HWI > CWT: p = 0.05, g = 0.43); improved sleep quality, compared with CON (p < 0.001, g = 1.15), CWI (p = 0.017, g = 0.70), and CWT (p = 0.018, g = 0.51); as well as increasing testosterone concentration (HWI > CWT: p = 0.038, g = 0.24). There were trivial to small (p < 0.001-0.039, g = 0.02-0.34) improvements (treatment effect) in jump performance (i.e., squat jump and countermovement jump) after all water immersion strategies, as compared with CON, with high variability in the individual responses. There were no significant differences (interaction effect, p > 0.05) observed between the water immersion intervention strategies and CON in performance (p = 0.153-0.99), hormone (p = 0.207-0.938), nor perceptual (p = 0.368-0.955) measures. To optimize recovery and performance responses, e.g., during an in-season competition phase, postresistance exercise HWI may assist with providing small-to-large improvements for up to 38 hours in perceived recovery (i.e., increased sleep quality and reduced fatigue) and increases in circulating testosterone concentration. Practitioners should consider individual athlete neuromuscular performance responses when prescribing postexercise hydrotherapy. These findings apply to athletes who aim to improve their recovery status, where postresistance exercise HWI optimizes sleep quality and next-day perceptions of fatigue.

The Influence of Music Preference on Countermovement Jump and Maximal Isometric Performance in Active Females

Previous studies have shown that listening to preferred music during resistance and endurance exercises improves performance. However, it is unknown if these phenomena translate to short-duration explosive exercises. The purpose of this study was to investigate the influences of preferred and non-preferred music on countermovement jump (CMJ) performance, isometric mid-thigh pull (IMTP), and psychological responses to music during explosive movements. Physically active females (age 18-25) volunteered to take part in the study. In a counterbalanced, crossover design, participants completed three trials: (1) no music (NM), (2) non-preferred (NP), and (3) preferred (PV) music. Participants completed three maximal IMTP tests on a force-plate-equipped IMTP apparatus with an immovable bar. Attempts lasted 5 s and were separated by 3 min of rest. Furthermore, participants completed three single maximal CMJ attempts separated by 3 min of rest on force plates. All attempts were averaged for analysis. At the commencement of IMTP and CMJ testing, participants were asked to rate how motivated and psyched up they felt during the exercise portion using a visual analog scale. For isometric performance, listening to PM resulted in increased peak force (p = 0.039; d = 0.41) and rate of force development at 200 ms (p = 0.023; d = 0.91) compared with NP. For CMJ, there were no differences between conditions for jump height (p = 0.912; η² = 0.007) or peak power during the propulsive phase (p = 0.460; η² = 0.003). Levels of motivation were significantly higher with PM compared with NM (p < 0.001; d = 2.3) and NP (p = 0.001; d = 2.0). Feelings of being psyched up were significantly higher with PM compared with NM (p < 0.001; d = 4.2) and NP (p = 0.001; d = 2.8). Findings suggest that preferred music enhances isometric strength and increases motivation and feelings of being psyched up. Thus, PM may be used as an ergogenic aid during short-duration maximal-effort activities.

Effects of Isometric Strength and Plyometric Training on Running Performance: A Randomized Controlled Study

Purpose: The aim of the study was to compare the effects of isometric strength (IST) and plyometric training (PT) on endurance running performance. Methods: Twenty-six endurance runners (18 males and 8 females; age 36 ± 6 years, stature 1.69 ± 0.05 m body mass 61.6 ± 8.0 kg, VO_2max 50.4 ± 5.8 ml·kg^-1·min^-1) completed the countermovement jump (CMJ), isometric mid-thigh pull (IMTP), 2.4 km run time trial (2.4kmTT), running economy test (RE) and a graded exercise test measures at baseline. They were then randomly assigned to three groups, the control (CON), PT or IST group, and completed the circuit, plyometric or isometric training, respectively, twice a week for 6 weeks, while still continuing to perform their planned running training. They then completed the same set of measures performed at baseline post-intervention. Results: Significant time x group interactions and time main effect were observed for 2.4kmTT (P = .002, ƞ²_p = .45 and P < .001, ƞ² =0.72), maximal aerobic speed (MAS) (P = .006, ƞ²_p = .39), CMJ height (P < .001, ƞ²_p = .55) and IMTP relative peak force (P = .001, ƞ²_p = .50) in favor of PT and IST. Significant main effect for time was observed for 2.4kmTT (P < .001, ƞ²_p = .72), RE (P = .048, ƞ²_p = .17), VO_2max (P = .047, ƞ²_p = .18), MAS (P < .001, ƞ²_p = .63), CMJ height (P < .001, ƞ²_p = .51) and IMTP relative peak force (P < .001, ƞ²_p = .58). Conclusion: In conclusion, both PT and IST were similarly effective at enhancing running endurance performance. However, IST resulted in greater improvement to RE.