Relationships between force-time characteristics of the isometric midthigh pull and dynamic performance in professional rugby league players

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.

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.

Using the Isometric Mid-Thigh Pull to Predict Three-Repetition Maximum Squat Values in Female Athletes

Prescribing correct training loads in strength- and power-based sports is essential to eliciting performance improvements for athletes. Concurrently, testing strength for the prescription of training loads should be accurate and safe with minimal disruption or fatigue inducement to the athlete. The purpose of this study was to develop a prediction equation in female athletes for the three-repetition maximum (3RM) squat using the isometric mid-thigh pull and basic anthropometric assessments that could be practically applied to support training prescriptions. Female athletes (n = 34) were recruited from netball, volleyball, basketball, and soccer across a spectrum of competitive standards. Each athlete's weight, standing height, seated height, arm span, and biacromial breadth were recorded, and then, on separate occasions separated by at least 48 h, each athlete completed a 3RM squat test and an isometric mid-thigh pull (IMTP) assessment. IMTP variables of peak force and time-dependent force at 50, 100, 150, 200, and 250 ms, as well as anthropometric measures, were used to develop a prediction equation. Squat strength was low-to-moderately correlated with peak force (r = 0.386); force at 100 ms (r = -0.128), 150 ms (r = -0.040), and 200 ms (r = -0.034); standing height (r = 0.294); and biacromial breadth (r = -0.410). Stepwise multiple regression significantly (p < 0.05) explained 26% of the 3RM squat strength variation using peak force and force at 100 ms, resulting in the following equation: Predicted 3RM squat (kg) = [6.102 + (Peak Force × 0.002) - (Force@100 ms × 0.001)]2. The reported equation's predictive accuracy was tested using the same testing protocols following 6-8 weeks of training in a sub-cohort of athletes (n = 14). The predicted and actual recorded 3RM values were not significantly (p = 0.313) different, supporting the use of the IMTP as a test that contributes informative values for use in a predictive equation for training prescription and thus reducing the testing and fatigue-inducing impost on female athletes. However, the 95% CI (-4.18-12.09) indicated predicted values could differ in excess of 10 kg. This difference could lead to an excessive load prescription for an athlete's training program, indicating caution should be taken if using the described method to predict 3RM squat values for programming purposes.

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.

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.

The Effects of Strength and Conditioning Interventions on Sprinting Performance in Team Sport Athletes: A Systematic Review and Meta-Analysis

Murphy, A, Burgess, K, Hall, AJ, Aspe, RR, and Swinton, PA. The effects of strength and conditioning interventions on sprinting performance in team sport athletes: a systematic review and meta-analysis. J Strength Cond Res 37(8): 1692–1702, 2023—Linear sprinting is a key determinant of athletic performance within team sports. The aims of the review were to quantify and compare the effectiveness of popular strength and conditioning (S&C) training modes to improve sprint performance in team sport athletes, with additional focus on potential moderators and the relationships between improvements in physical factors (e.g., strength, power, and jump performance) and improvements in sprint performance. Inclusion was restricted to resistance, plyometric, sprint, and combined training interventions comprising team sport athletes. Multilevel, Bayesian’s meta-analysis and meta-regression models conducted with standardized mean difference effect sizes were used to investigate training modes and potential moderators. Weighted regression models conducted on shrunken estimates from initial Bayesian’s meta-analyses were used to quantify relationships between improvements in physical factors and sprint performance. Certainty of evidence was assessed using the grading of recommendations assessment development and evaluation (GRADE) approach. Similar improvements in sprint performance were obtained across training modes, with some evidence of the largest effects with resistance training ( = 0.55 [95% credible interval [CrI]: 0.36–0.78; very low certainty]). A strong moderating effect of training intensity was identified across all training modes with evidence of greater improvements in sprint performance with high-intensity training ( = 0.17 [95% CrI: 0.01–0.33; very low certainty]). Strong positive relationships were identified between improvements in all physical factors and sprint performance ( = 0.56 [95% CrI: 0.36–0.77; low certainty], = 0.80 [95% CrI: 0.50–1.0; low certainty], = 0.78 [95% CrI: 0.57–0.97; low certainty]). The findings indicate that focus on developing speed in team sport athletes should be placed on S&C training with high intensities, including the use of resisted sprint training.

Delayed Effect of Dry-Land Strength Training Sessions on Swimming Performance

The purpose of the study was to examine the effects of dry-land strength endurance (SE) and maximum strength (MS) sessions on next-day swimming performance. Eight swimmers (age: 18.6 ± 2.9 years) performed evening training sessions (19:00-19:40), including: (i) SE (2 × 15 - 20 repetitions, 50% of 1-RM), (ii) MS (2 × 5 repetitions, 90% of 1-RM), (iii) control (CON: no dry-land training). All sessions were followed by a 90-min swimming training (20:00-21:30). Medicine ball throw and countermovement jump, free countermovement jump and squat jump were evaluated before and after the dry-land training session and 12 h later, before a 100-m front crawl sprint (next day at 8:30 a.m.). Performance time, RPE, blood lactate and biomechanical variables in 100-m sprint were no different between conditions (time, MS: 64.70 ± 7.35, SE: 63.81 ± 7.29, CON: 64.52 ± 7.71 s, p > 0.05). Jump height was not changed before and after dry-land and before the 100-m sprint in all conditions (p > 0.05). Medicine ball throw was lower in MS compared to CON before the 100-m sprint (MS: 4.44 ± 1.11, vs. CON: 4.66 ± 1.21 m, p < 0.05). Upper-body but not lower- body muscle function may be affected by MS training. However, performance in a 100-m test is not affected by dry-land training performed 12 h earlier.

Scoping Review of the Isometric Mid-Thigh Pull Performance Relationship to Dynamic Sport Performance Assessments

Attempting to understand on-field sport performance from dynamic performance tests of athleticism (i.e., sprinting, jumping, strength) is common practice in sport. In recent years, the isometric mid-thigh pull (IMTP) has gained popularity in the sport performance community as an assessment tool. This scoping review examined the relationship of the IMTP to common dynamic sports assessments to evaluate the robustness of the IMTP to profile lower body force production characteristics. The literature search was conducted according to PRISMA-ScR guidelines. Articles were selected from 5 electronic databases. Data was extracted and synthesized to evaluate the reported relationships between IMTP and common dynamic sport performance assessments. Forty-eight publications were identified and included in the review. Articles reviewed were all within the past 25 years with most (66.7%) published within the past 5 years. Multiple researchers utilized the IMTP across numerous sports and generally reported consistent results. Strong correlations (41.8% of reported, r = 0.71 to 1.00) between the IMTP and the dynamic sport performance assessments were found. The available evidence suggests the IMTP is a viable option for practitioners and researchers to use to profile athletic ability. Furthermore, based on the publication year of included articles, IMTP research is relatively young and warrants further investigation.

Progressive Loading in a Strongman Following Distal Biceps Repair: Re-Thinking Load Progression - A Case Report

Background

Rupture of the distal biceps is relatively rare and post-operative protocols are typically vague and are used on many patients, regardless of pre-morbid status. The primary objective is to share the progressive loading strategy used in the rehabilitation of a strongman athlete following a surgical repair of the distal biceps. An additional objective is to highlight the need for individualized protocols and progressions with respect to patient goals and sport demands, as well as the need for shared decision making (SDM) between the medical doctor, patient, and rehabilitation provider.

Case Presentation

The subject is a 39-year-old strong man competitor who suffered a distal biceps rupture while doing a tire flip during training. After having it repaired, the post-operative recovery was unremarkable. The focus of the described intervention was establishing load during rehabilitation exercises that were unique to this individual based on his pre-morbid level of strength and training history as well as the unique demands of his sport.

Outcomes

The patient achieved symmetrical isokinetic strength of the elbow flexors at 60°/second in supine at six months post-operative.

Discussion

The case highlights a successful outcome in a strongman competitor with a distal biceps rupture repair. Typically, protocols are vague and lack specific standards for establishment of load for exercises. Often starting points and progressions are arbitrary and lack rationale tailored to individual needs and/or pre-morbid status. The case offers a framework for establishing and progressing load while also discussing how a shared decision-making model can lead to positive outcomes.

Joint-level determinants of the dynamic strength index: implications for testing and monitoring

The aims of this study were to determine the associations and differences between the traditional dynamic strength index (DSIGRF, calculated from ground reaction force [GRF] data) and joint-level dynamic strength indices (DSINJM, calculated from net joint moment [NJM] data). Eight female NCAA Division I lacrosse players performed three maximal effort isometric mid-thigh pulls (IMTP) and countermovement jumps (CMJ). GRF and motion capture data were recorded and used to calculate hip, knee, and ankle NJM. The ratio between peak forces during the IMTP and CMJ tests was used to calculate the DSIGRF and the ratio of peak NJM was used to calculate ankle, knee, and hip DSINJM. Associations and differences between DSIGRF and DSINJM were examined with Pearson's correlation coefficients, paired t-tests and Hedge's g effect sizes. The results showed that only the hip DSINJM was correlated with DSIGRF (hip: p = 0.037; r = 0.738). In addition, athletes exhibited significantly greater DSINJM than DSIGRF. Although these results suggest DSIGRF are associated with hip DSINJM, the fact that joint-level DSINJM were generally greater than DSIGRF suggests the ratio between peak NJM during the CMJ and IMTP may not provide intuitive or useful data for strength and conditioning coaches or sport scientists.

Norm Values of Muscular Strength Across the Life Span in a Healthy Swiss Population: The COmPLETE Study

BACKGROUND

Grip strength is used to estimate whole-body strength for health surveillance purposes. Explosive strength is considered important, yet economic measures able to detect early deterioration of neuromuscular capabilities are lacking. Whether handgrip maximum rate of force development (GRFD) or whole-body strength tests are better predictors of lower body power than handgrip maximum strength (GF_max) and their trajectories throughout the life span are unknown.

HYPOTHESIS

GRFD should be more closely related to lower body power than GF_max, and its trajectories over the life span should more closely follow that of lower body power.

STUDY DESIGN

Cross-sectional.

LEVEL OF EVIDENCE

Level 2b.

METHODS

A total of 613 healthy participants aged 20 to 91 years were tested for countermovement jump peak power, GF_max, handgrip rate of force development, and midthigh pull peak force (MTP). Cubic splines and linear models were built for age trajectories, generalized additive models for quintile curves, and linear regression was used to assess predictive quality.

RESULTS

Peak power (P_max) declined linearly to 60% of young adult level, with GRFD, GF_max, and MTP remaining stable up to age 50 years and then declining more sharply to 52% to 71% of young adult levels. Trajectories were similar for male and female participants. GRFD (β = 0.17) and MTP (β = 0.08) were worse predictors of P_max than GF_max (β = 0.24) in models adjusted for age, sex, lean body mass, and vigorous physical activity levels.

CONCLUSION

GRFD was not superior to maximum strength in predicting lower body power. For health surveillance purposes, it therefore appears that GF_max tests are more economical and equally good predictors of lower body explosive strength at older age. The data provided can be used as norm values for healthy subjects.

CLINICAL RELEVANCE

Incorporating countermovement jump testing for early detection of declines in explosive capabilities might be advised.

Strength Training in Swimming

This narrative review deals with the topic of strength training in swimming, which has been a controversial issue for decades. It is not only about the importance for the performance at start, turn and swim speed, but also about the question of how to design a strength training program. Different approaches are discussed in the literature, with two aspects in the foreground. On the one hand is the discussion about the optimal intensity in strength training and, on the other hand, is the question of how specific strength training should be designed. In addition to a summary of the current state of research regarding the importance of strength training for swimming, the article shows which physiological adaptations should be achieved in order to be able to increase performance in the long term. Furthermore, an attempt is made to explain why some training contents seem to be rather unsuitable when it comes to increasing strength as a basis for higher performance in the start, turn and clean swimming. Practical training consequences are then derived from this. Regardless of the athlete's performance development, preventive aspects should also be considered in the discussion. The article provides a critical overview of the abovementioned key issues. The most important points when designing a strength training program for swimming are a sufficiently high-load intensity to increase maximum strength, which in turn is the basis for power, year-round strength training, parallel to swim training and working on the transfer of acquired strength skills in swim training, and not through supposedly specific strength training exercises on land or in the water.

Is Ischemic Preconditioning Intervention Occlusion-Dependent to Enhance Resistance Exercise Performance?

ABSTRACT

de Souza, HLR, Arriel, RA, Hohl, R, da Mota, GR, and Marocolo, M. Is ischemic preconditioning intervention occlusion-dependent to enhance resistance exercise performance? J Strength Cond Res 35(10): 2706-2712, 2021-Ischemic preconditioning is a rising technique with potential to improve performance. Currently, its effects are still controversial, and a placebo effect seems to have a role. In this sense, this study evaluated the effect of high-pressure (HP) and low-pressure (LP) cuffing on resistance exercise performance during repeated 5-day intervention. Twenty healthy trained men (24.0 ± 4.4 years; 80.1 ± 12.2 kg; and 176.9 ± 6.6 cm) performed a 1 repetition maximum (1RM) test before interventions. Maximal isometric force test, number of repetitions (75% 1RM), total workload (sets × reps × load), fatigue index (FI) ([set 1 - set 3]/set 1 × 100), and perceived scales were assessed during knee extension preceded by HP (3 × 5-minute unilateral leg occlusion at 50 mm Hg above systolic blood pressure), LP (3 × 5-minute unilateral leg occlusion at 20 mm Hg), or control ([CON] 30-minute resting). The main effect of cuff intervention was significant for total workload (F(1,16) = 4.2, p = 0.03) after adjusting for baseline (analysis of covariance). Adjusted means (confidence interval) and effect sizes (ES) indicate that HP (1778 kg [1,613-1944]; ES: 0.29) and LP (1761 kg [1,590-1932]; ES: 0.34) significantly increased total workload compared with CON (1,452 kg [1,262-1,643]; ES: 0.17). Finally, isometric force and FI were similar for all conditions (HP, LP, and CON) with no difference from baseline performance. In conclusion, the short-term (5-day) intervention of HP and LP cuffing increases the total workload. This effect in muscle endurance performance is nondependent of blood flow occlusion, since LP is not able to obstruct arterial blood flow. A likely motivational effect cannot be ruled out.

Maximal Strength in Relation to Force and Velocity Patterns During Countermovement Jumps

Maximal strength is important for the performance of dynamic athletic activities, such as countermovement jumps (CMJ). Although measures of maximal strength appear related to discrete CMJ variables, such as peak ground reaction forces (GRF) and center-of-mass (COM) velocity, knowledge about the association between strength and the time series patterns during CMJ will help characterize changes that can be expected in dynamic movement with changes in maximal strength.

PURPOSE

To investigate the associations between maximal strength and GRF and COM velocity patterns during CMJ.

METHODS

Nineteen female college lacrosse players performed 3 maximal-effort CMJs and isometric midthigh pull. GRF and COM velocity time series data from the CMJ were time normalized and used as inputs to principal-components analyses. Associations between isometric midthigh pull peak force and CMJ principal-component scores were investigated with a correlational analysis.

RESULTS

Isometric midthigh pull peak force was associated with several GRF and COM velocity patterns. Correlations indicated that stronger players exhibited a GRF pattern characterized by greater eccentric-phase rate of force development, greater peak GRF, and a unimodal GRF profile (P = .016). Furthermore, stronger athletes exhibited a COM velocity pattern characterized by higher velocities during the concentric phase (P = .004).

CONCLUSIONS

Maximal strength is correlated to specific GRF and COM velocity patterns during CMJ in female college lacrosse athletes. Since maximal strength was not correlated with discrete CMJ variables, the patterns extracted via principal-components analyses may provide information that is more beneficial for performance coaches and researchers.

Unilateral Maximal Isometric Hex Bar Pull Test: Within-Session Reliability and Lower Body Force Production in Male and Female Freeski Athletes

The aim of the study was to (1) assess the within-session reliability of a unilateral isometric hex bar pull (UIHBP) maximal voluntary contraction (MVC) test and, (2) determine unilateral isometric absolute peak force (PFabs) and relative peak force (PF) values in freeski athletes. Twenty-one male and eight female academy to national team freeskiers performed the novel UIHBP MVC task on a force plate and PFabs and relative PF were assessed (1000 Hz). Within-session measures of PFabs offered high reliability on left and right limbs for males (ICC = 0.91-0.94, CV = 2.6-2.2%) and females (ICC = 0.94-0.94, CV = 1.4-1.6%), while relative PF measures showed good to high reliability in both left and right limbs for males (ICC = 0.8-0.84, CV = 2.6-2.2%) and females (ICC = 0.92-0.90, CV = 1.4-1.7%). We observed significantly lower PFabs (p < 0.001) and relative PF (p < 0.001) in females compared to males. No statistical difference was found between left and right limbs in males and females in PFabs (p = 0.98) and relative PF measures (p = 0.93). The UIHBP MVC test appears to be a reliable method for assessing PFabs and relative PF in male and female freeski athletes.

Influence of the Bar Position on Joint-Level Biomechanics During Isometric Pulling Exercises

ABSTRACT

Ahn, N, Kim, H, Krzyszkowski, J, Roche, S, and Kipp, K. Influence of the bar position on joint-level biomechanics during isometric pulling exercises. J Strength Cond Res 35(6): 1484-1490, 2021-The purpose of this study was to investigate the influence of the bar position on ankle, knee, and hip net joint moments (NJMs), relative muscular effort (RME), and vertical ground reaction forces (GRFs) during isometric pulling exercises, such as the isometric midthigh pull. Eight female lacrosse athletes performed maximal effort isometric pulls at 3 different bar positions (low: above patella, mid: midthigh, and high: crease of hip) while motion capture and GRF data were recorded. Net joint moments were calculated with inverse dynamics. Relative muscle effort was defined as the ratio between the inverse dynamics NJMs and the maximum theoretical NJMs, which were estimated with regression-based maximum moment-angle models. Peak NJM and RME were compared with 2-way analyses of variance (ANOVA), whereas GRFS were compared with a 1-way ANOVA. Peak vertical GRF were significantly greater in the mid bar position than the high bar position but did not differ between the low and mid bar position. Bar position significantly influenced peak hip and knee NJM and RME. Hip NJM and RME were greatest in the low bar position, whereas knee NJM and RME were greater in the mid bar position. Because hip and knee extensor NJM and RME differed between the low and mid bar positions, but the GRFS did not, the joint-specific contributions to peak isometric pulling forces likely reflected a trade-off between hip dominance and knee dominance in the low and mid bar position, respectively. This information should be considered in the interpretation isometric pulling data and their use in assessing and monitoring maximal force-producing capacity of the lower body.

Anthropometric Profiles and Physical Characteristics in Competitive Female English Premiership Rugby Union Players

Rugby union (RU) is a field-based team sport with a large number of high-intensity actions such as sprinting, change of direction, tackling, scrummaging, rucking, and mauling. Competitive success in female RU has previously been related to anthropometric and physical characteristics, and with the recent introduction of professionalism in female rugby, characterizing such physical attributes may provide insight into selection and training processes.

PURPOSE

To identify anthropometric and physical characteristics of competitive female RU players and differences between playing positions.

METHODS

Twenty-two players were recruited from the top tier of female RU in the United Kingdom during the 2018-2019 Premiership season. Players were split into forwards and backs and underwent body composition testing via dual-X-ray absorptiometry and physical characteristic tests (10- and 20-m speed, 1-repetition-maximum bench press and squat, countermovement jump, drop jump, isometric midthigh pull, and 1200-m shuttle).

RESULTS

Moderate to large significant differences between playing positions in both anthropometric and physical characteristics were found (P < .01). Forwards displayed greater body mass (P = .03), fat mass (P = .01), and absolute upper-body strength (P = .03), whereas backs demonstrated superior countermovement jump height (P = .01), drop jump height (P = .01), greater reactive strength (P = .03), and speed (P = .03).

CONCLUSION

These findings provide practitioners with a greater understanding of anthropometric and physical characteristics of professional female RU players.

Relationship Between Tennis Serve Velocity and Select Performance Measures

ABSTRACT

Hayes, MJ, Spits, DR, Watts, DG, and Kelly, VG. Relationship between tennis serve velocity and select performance measures. J Strength Cond Res 35(1): 190-197, 2021-The purpose of this study was to determine whether there was a relationship between tennis serve speed and isometric midthigh pull (IMTP) kinetic variables: countermovement jump (CMJ) height, shoulder internal and external rotation strength, and anthropometric measures in elite adolescent tennis players. Twenty-one elite junior tennis players from the Tennis Australia National Academy were recruited for this study (male, n = 12 and female, n = 9). Correlations between the performance variables and peak tennis serve speed were calculated using a Pearson's product-moment correlation coefficient. A significant positive correlation was found between peak serve speed and body height (r = 0.80, p < 0.01), IMTP peak force (r = 0.87, p < 0.01), CMJ height (r = 0.77, p ≤ 0.01), and impulse at 300 ms (r = 0.71, p ≤ 0.01). A significant, strong correlation was found between peak serve speed and impulse at 100 ms (r = 0.58, p ≤ 0.01), impulse at 200 ms (r = 0.64, p ≤ 0.01), internal rotation <90° (r = 0.63, p ≤ 0.01), and external rotation <90° (r = 0.63, p ≤ 0.01). Because of the significant positive correlations between IMTP variables, CMJ height and peak serve speed, strength and conditioning coaches with access to a force plate should consider using the IMTP to athletically profile athletes in regards to their strength, power, and injury risk.

Isometric Mid-Thigh Pull Performance in Rugby Players: A Systematic Literature Review

The isometric mid-thigh pull (IMTP) is a multi-joint test of whole-body force production relevant to rugby players. "Rugby AND (mid-thigh pull OR midthigh pull OR mid thigh pull" were searched in PubMed, Sportdiscus, Academic Search Premier, CINAHL Plus with Full Text, and Google Scholar; the final date of search was 24 January 2018. Data extraction from 24 articles included subject characteristics, force data, and IMTP testing procedures. Select ranges of peak forces reported were: Youth: 1162-2374 N; Academy: 1855-3104 N; Professional: 2254-3851 N. Rate of force development (RFD) at 100 and 200 ms ranged from 5521 to 11,892 N and 5403 to 8405 N, respectively, among professional rugby players. Studies' research design were of moderate quality, but most studies lacked detailed reporting of IMTP procedures. Variability of force characteristics derived from the IMTP within similar populations (e.g., approximately 200% difference in peak force between samples of professional rugby league players) as well as large and unexpected overlaps between dissimilar populations, limit conclusions about force production capabilities relative to playing level, likely due to limitations and lack of standardization of IMTP procedures. Greater uniformity in IMTP testing procedures and reporting is needed. This manuscript provides a guide for reporting needs when presenting results from an IMTP in research.

The relationship between isometric mid-thigh pull variables and athletic performance measures: empirical study of English professional soccer players and meta-analysis of extant literature

BACKGROUND

There is currently limited evidence available to support the use of the isometric mid-thigh pull (IMTP) within professional soccer. The aim of this study was to analyze the association between IMTP variables, with common markers of athletic performance capability.

METHODS

Eleven professional development soccer players (age: 20±2 years, stature: 1.82±0.10 m, mass: 76.4±12.8 kg) performed IMTP, 5 m and 10 m accelerations, maximal sprint speed (MSS), countermovement jump (CMJ), and the 505 change of direction test (COD).

RESULTS

Relative and absolute peak force (PF) and force at 50, 100, 150 and 200 ms values were measured during the IMTP. Relative F150, F200, PF displayed large to very large correlations with MSS (r=0.51, r=0.66, and r=0.76 respectively), while absolute PF also displayed a large correlation with MSS (r=0.57). Relative and absolute PF showed large correlations with CMJ height (r=0.54 and r=0.55 respectively). Relative F150 and F200 highlighted large correlations with COD ability (r=-0.68 and r=-0.60 respectively). Relative F200 and PF had a large negative correlation with 10 m acceleration (r=-0.55 and r=-0.53 respectively).

CONCLUSIONS

This study provides an important contribution to knowledge within the area of IMTP testing in professional soccer by evidencing the prominence of the isometric force generating capacity as an underpinning factor in relation to athletic capability.

The Reliability of Neuromuscular and Perceptual Measures Used to Profile Recovery, and the Time-Course of such Responses following Academy Rugby League Match-Play

In professional academy rugby league (RL) players, this two-part study examined; A) the within- and between-day reliability of isometric mid-thigh pulls (IMTP), countermovement jumps (CMJ), and a wellness questionnaire (n = 11), and B) profiled the responses with acceptable reliability (no between-trial differences and between-day coefficient of variation (CV) ≤10% and intraclass correlation coefficient (ICC) ≥0.8) for 120 h (baseline: -3, +24, +48, +72, +96, +120 h) following RL match-play (n = 10). In part A, force at 200, and 250 ms, and peak force (PF) demonstrated acceptable within- (CV%: 3.67-8.41%, ICC: 0.89-0.93) and between-day (CV%: 4.34-8.62%, ICC: 0.87-0.92) reliability for IMTP. Most CMJ variables demonstrated acceptable within-day reliability (CV%: 3.03-7.34%, ICC: 0.82-0.98), but only six (i.e., flight-time, PF, peak power (PP), relative PP, velocity at take-off (VTO), jump-height (JH)) showed acceptable between-day reliability (CV%: 2.56-6.79%, ICC: 0.83-0.91). Only total wellness demonstrated acceptable between-day reliability (CV%: 7.05%, ICC: 0.90) from the questionnaire. In part B, reductions of 4.75% and 9.23% (vs. baseline; 2.54 m∙s-1; 0.33 m) occurred at +24 h for CMJ VTO, and JH, respectively. Acceptable reliability was observed in some, but not all, variables and the magnitude and time-course of post-match responses were test and variable specific. Practitioners should therefore be mindful of the influence that the choice of recovery monitoring tool may have upon the practical interpretation of the data.

The Relationship between Isometric Force-Time Characteristics and Dynamic Performance: A Systematic Review

The purpose of this article was to review the data on the relationship between multi-joint isometric strength test (IsoTest) force-time characteristics (peak force, rate of force development and impulse) and dynamic performance that is available in the current literature. Four electronic databases were searched using search terms related to IsoTest. Studies were considered eligible if they were original research studies that investigated the relationships between multi-joint IsoTest and performance of dynamic movements; published in peer-reviewed journals; had participants who were athletes or active individuals who participate in recreational sports or resistance training, with no restriction on sex; and had full text available. A total of 47 studies were selected. These studies showed significant small to large correlations between isometric bench press (IBP) force-time variables and upper body dynamic performances (r² = 0.221 to 0.608, p < 0.05) and significant small to very large correlation between isometric squat (ISqT) (r² = 0.085 to 0.746, p < 0.05) and isometric mid-thigh pull (IMTP) (r² = 0.120 to 0.941, p < 0.05) force-time variables with lower body dynamic performances. IsoTest force-time characteristics were shown to have small to very large correlations with dynamic performances of the upper and lower limbs as well as performance of sporting movements (r² = 0.118 to 0.700, p < 0.05). These data suggest that IsoTest force-time characteristics provide insights into the force production capability of athletes which give insight into dynamic performance capabilities.

Changes in Early and Maximal Isometric Force Production in Response to Moderate- and High-Load Strength and Power Training

Comfort, P, Jones, PA, Thomas, C, Dos'Santos, T, McMahon, JJ, and Suchomel, TJ. Changes in early and maximal isometric force production in response to moderate- and high-load strength and power training. J Strength Cond Res XX(X): 000-000, 2020-The aims of this study were to determine the changes in early (50-, 100-, 150-, 200-, 250 ms) and maximal isometric force production, in response to a 4-week period of moderate-load resistance training (60-82.5% 1 repetition maximum [1RM]), followed by a 4-week period of high-load (80-90% 1RM) resistance training. Thirty-four subjects (age 19.5 ± 2.8 years; height 1.72 ± 0.08 m; body mass 69.9 ± 11.4 kg; maximal power clean 0.92 ± 0.03 kg·kg) participated in this study. Only trivial-to-moderate (0.2-2.7%, d = 0.00-0.88) and nonsignificant (p > 0.05) changes in early isometric force production were observed in response to the moderate-load training period, whereas very large (9.2-14.6%, d = 2.71-4.16), significant (p ≤ 0.001) increases in early isometric force production were observed in response to high-load training. In contrast, there was a very large, significant increase in peak force (PF) across the moderate-load phase (7.7 ± 11.8%, d = 2.02, p = 0.003), but only a moderate significant increase in PF (3.8 ± 10.6%, d = 1.16, p = 0.001) across the high-load phase. The results of this study indicate that high-load multijoint resistance training, that follows moderate-load training, results in superior increases in early multi-joint force production, compared with the changes observed after moderate-load resistance training.

Influence of Reactive and Maximum Strength Indicators on Sprint Performance

Healy, R, Smyth, C, Kenny, IC, and Harrison, AJ. Influence of reactive and maximum strength indicators on sprint performance. J Strength Cond Res 33(11): 3039-3048, 2019-The primary aim of this study was to assess the relationship between reactive and maximal strength measures with 40 m sprint performance and mechanical properties. Fourteen male and 14 female sprinters participated in this study. On the first day, subjects performed 40 m sprints with 10-m split times recorded in addition to maximal theoretical velocity, maximal theoretical force and peak horizontal power, which were calculated from force-velocity relationships. On the second day, subjects performed isometric midthigh pulls (IMTPs) with peak force (PF) and relative PF calculated, drop jumps (DJs) and vertical hopping where the reactive strength index (RSI) was calculated as jump height (JH) divided by contact time (CT). Pearson correlations were used to assess the relationships between measures and independent samples t-tests were used to assess the differences between men and women. No significant correlations were found between DJ and hopping RSI and sprint measures. A significant strong positive correlation was found between IMTP PF and peak horizontal power in men only (r = 0.61). The male sprinters performed significantly better in all recorded measures apart from hopping (CT, JH and RSI) and DJ CT where no significant differences were found. The lack of association between reactive and maximal strength measures with sprint performance is potentially because of the test's prolonged CTs relative to sprinting and the inability to assess the technical application of force. Several methods of assessing reactive strength are needed that can better represent the demands of the distinct phases of sprinting e.g., acceleration, maximum velocity.

The Relationship Between Isometric Strength and Sprint Acceleration in Sprinters

PURPOSE

To examine the relationships between the isometric midthigh pull (IMTP), isometric squat (ISqT), and sprint acceleration performance in track-and-field sprinters and to determine whether there are differences between men and women.

METHODS

Fifteen male and 10 female sprinters performed 3 maximal-effort IMTPs, ISqTs, and 3 × 30-m sprints from blocks.

RESULTS

Among the men, the results showed significant negative correlations between IMTP and ISqT peak force; relative peak force; force at 100, 150, and 200 ms; rate of force development (0-150 and 0-200 ms); and impulse (0-200 ms) and 0- to 5-m time (r = -.517 to -.714; P < .05). IMTP impulse (B = -0.582, P = .023) and ISqT relative peak force (B = -0.606, P = .017) significantly predicted 0- to 5-m time. Among the women, no IMTP or ISqT variables significantly correlated with any sprint times. Men measured significantly higher than women for all IMTP measures except relative peak force. Men were significantly faster than women at all splits. When comparing measures of the ISqT, there were no significant differences between men and women.

CONCLUSIONS

Variables measured during the IMTP and ISqT significantly correlated with 0- to 5-m sprint performance in male athletes. Isometric strength can have a sizable influence on 0- to 5-m time, but in some cases, the maximum effect could be very small.

Isometric Midthigh Pull Performance Is Associated With Athletic Performance and Sprinting Kinetics in Division I Men and Women's Basketball Players

Townsend, JR, Bender, D, Vantrease, WC, Hudy, J, Huet, K, Williamson, C, Bechke, E, Serafini, PR, and Mangine, GT. Isometric midthigh pull performance is associated with athletic performance and sprinting kinetics in Division I men and women's basketball players. J Strength Cond Res 33(10): 2665-2673, 2019- The relationships between isometric mid-thigh pull (IMTP) force, athletic performance measures, and sprint kinetics in Division I men's and women's basketball players were investigated. Twenty-three (male = 8, female = 15) Division 1 basketball players completed a maximal 20-m sprint trial while tethered to a device that provided kinetic feedback (peak and average sprinting power, velocity and force). Additionally, 1 repetition maximum (1RM) front squat, 1RM hang clean, vertical jump height, and agility (proagility and lane agility) tests were performed. Rate of force development (RFD) at 50, 100, 150, 200 and 250 milliseconds of IMTP and peak force (PF) were also collected. Pearson's product-moment correlation analysis was used to examine the relationships between these measures. Significant (p ≤ 0.05) relationships were observed between IMTP PF and sprint time over all distances (5-20 m; r = -0.62 to 0.69), average sprint velocity (r = 0.50-0.70), peak sprint velocity (r = 0.50-0.54), average sprint force (r = 0.48-0.69), and average sprint power (r = 0.62-0.73). Sprinting kinetic measures (average force and power) over the first 5 m were also significantly (p ≤ 0.05) related to IMTP RFD (50-250 ms; r = 0.42-0.62). Results indicate that IMTP variables are significantly associated with 20-m sprint kinetics. Specifically, IMTP RFD appears to be related to the initial acceleration kinetics of a sprint. Strength and conditioning professionals can possibly implement the IMTP for improved assessment and monitoring of athletic performance and training.

Duration-Dependent Effects of Passive Static Stretching on Musculotendinous Stiffness and Maximal and Rapid Torque and Surface Electromyography Characteristics of the Hamstrings

Palmer, TB, Pineda, JG, Cruz, MR, and Agu-Udemba, CC. Duration-dependent effects of passive static stretching on musculotendinous stiffness and maximal and rapid torque and surface electromyography characteristics of the hamstrings. J Strength Cond Res 33(3): 717-726, 2019-This study aimed to examine the effects of stretching duration on passive musculotendinous stiffness and maximal and rapid torque and surface electromyography (EMG) characteristics of the hamstrings. Thirteen young females (age = 21 ± 2 years) underwent 2 passive straight-leg raise (SLR) assessments and 2 isometric maximal voluntary contractions (MVCs) of the hamstrings before and after 4 randomized conditions that included a control treatment and 3 experimental treatments of passive static stretching for 30-, 60-, and 120-second durations. Passive stiffness was calculated during each SLR as the slope of the final 10% of the angle-torque curve. Isometric peak torque (PT), rate of torque development (RTD), peak EMG amplitude (PEMG), and rate of EMG rise (RER) were extracted from each MVC. Results indicated that PT and PEMG were not affected (p = 0.993 and 0.422, respectively) by any of the experimental treatments. Rate of torque development and RER decreased from pre- to post-treatment for 120 seconds (p = 0.001 and 0.001) but not for the control (p = 0.616 and 0.466), 30- (p = 0.628 and 0.612), and 60-second (p = 0.396 and 0.815) interventions. The slope coefficient decreased from pre- to post-treatment for the 30- (p = 0.001), 60- (p = 0.002), and 120-second (p = 0.001) stretching interventions but not for the control (p = 0.649). Given the significant stiffness reductions and lack of changes in PT and RTD for the 30- and 60-second interventions, it may be advantageous for practitioners who are using hamstring passive stretching as part of a warm-up routine, to perform such stretching on their clients for short (30-60 seconds) rather than moderate (120-second) stretching durations.

Neuromuscular, physiological and perceptual responses to an elite netball tournament

To examine responses to an International netball tournament, female athletes (n= 11) played three matches over consecutive days. External (accelerometry) and internal (heart rate; HR, session; sRPE, and differential; dRPE, rating of perceived exertion) load measures quantified match intensity. On match-day mornings, and three days after match 3, well-being (brief assessment of mood; BAM+), biochemical (creatine kinase concentration; CK), neuromuscular (jump height; JH, peak power output; PPO) and endocrine function (salivary cortisol; C, testosterone; T, concentrations) were assessed. External load was similar between matches whereas dRPE and sRPE were greatest for match 3. Following match 1, CK increased, whereas BAM+, JH, C and T decreased. Following two matches, BAM+, PPO, and T decreased with CK increasing versus baseline. Following consecutive matches, CK (likely moderate; 27.9% ± 19.5%) and C (possibly moderate; 43.3% ± 46.8%) increased, whilst BAM+ (possibly moderate; -20.6% ± 24.4%) decreased. Three days post-tournament BAM+, T, PPO, and JH decreased. Mid-court elicited higher mean HR (possibly moderate; 3.7% ± 3.8%), internal and external intensities (possibly very large; 85.7% ± 49.6%) compared with goal-based positions. Consecutive matches revealed a dose-response relationship for well-being and physiological function; a response evident three days post-tournament.

Effect of Sampling Frequency on Isometric Midthigh-Pull Kinetics

PURPOSE

Skeletal-muscle function can be evaluated using force-times curves generated via the isometric midthigh pull (IMTP). Various sampling frequencies (500-1000 Hz) have been used for IMTP assessments; however, no research has investigated the influence of sampling frequency on IMTP kinetics. Therefore, the purpose of this study was to investigate the influence of sampling frequency on kinetic variables during the IMTP, including peak force, time-specific force values (100, 150, and 200 ms), and rate of force development (RFD) at 3 time bands (0-100, 0-150, 0-200 ms).

METHODS

Academy rugby league players (n = 30, age 17.5 ± 1.1 y, height 1.80 ± 0.06 m, mass 85.4 ± 10.3 kg) performed 3 IMTP trials on a force platform sampling at 2000 Hz, which was subsequently down-sampled to 1500, 1000, and 500 Hz for analysis.

RESULTS

Intraclass correlation coefficients (ICC) and coefficients of variation (CV) demonstrated high within-session reliability for all force and RFD variables across all sampling frequencies (ICC ≥ .80, CV ≤ 14.4%) except RFD 0-100 and 0-150, which demonstrated slightly greater levels of variance (CV = 18.0-24.1%). Repeated-measures analysis of variance revealed no significant differences (P > .05, Cohen d ≤ 0.0171) in kinetic variables between sampling frequencies. Overall, high reliability was observed across all sampling frequencies for peak force, time-specific force, and RFD 0- to 200-ms variables, with no significant differences (P > .05) for each kinetic variable across sampling frequencies.

CONCLUSIONS

Practitioners and scientists may consider sampling as low as 500 Hz when measuring peak force, time-specific force values, and RFD at predetermined time bands during the IMTP for accurate and reliable data.

Between-Session Reliability of Isometric Midthigh Pull Kinetics and Maximal Power Clean Performance in Male Youth Soccer Players

Dos'Santos, T, Thomas, C, Comfort, P, McMahon, JJ, Jones, PA, Oakley, NP, and Young, AL. Between-session reliability of isometric midthigh pull kinetics and maximal power clean performance in male youth soccer players. J Strength Cond Res 32(12): 3373-3381, 2018-The aim of the study was to determine the between-session reliability of isometric midthigh pull (IMTP) kinetics and maximal weight lifted during the power clean (PC) in male youth soccer players, and to identify the smallest detectable differences between sessions. Thirteen male youth soccer players (age: 16.7 ± 0.5 years, height: 1.80 ± 0.08 m, and mass: 70.5 ± 9.4 kg) performed 3 IMTP trials, whereas only 10 soccer players performed maximal PCs. These were performed twice, separated by 48 hours to examine the between-session reliability. Intraclass correlation coefficients (ICCs) and coefficient of variation (CV) demonstrated high levels of within-session (ICC = 0.84-0.98, CV = 4.05-10.00%) and between-session reliability (ICC = 0.86-0.96, CV = 3.76-7.87%) for IMTP kinetics (peak force [PF] and time-specific force values 30-250 ms) and maximal PC (ICC = 0.96, CV = 3.23%), all meeting minimum acceptable reliability criteria. No significant differences (p > 0.05, effect size ≤0.22) were revealed between sessions for IMTP kinetics and maximal PC performance. Strength and conditioning coaches and practitioners should consider changes of >6.04% in maximal PC and changes in IMTP kinetics of >14.31% in force at 30 ms, >14.73% in force at 50 ms, >12.36% in force at 90 ms, >12.37% in force at 100 ms, >14.51% in force at 150 ms, >11.71% in force at 200 ms, >7.23% in force at 250 ms, and >8.50% in absolute PF as meaningful improvements in male youth soccer players. Decrements in the IMTP kinetics greater than the aforementioned values could possibly be used as an indicator of neuromuscular fatigue and preparedness for training or competition.

Explosive voluntary torque is related to whole-body response to unexpected perturbations

Explosive torque has been demonstrated to relate to static balance. However, sports injuries occur dynamically and unpredictably, yet the relationship between explosive torque and balance response to dynamic perturbations is unknown. This study investigated the relationship between explosive torque of the plantar flexors and knee extensors and the centre of mass (COM) response to unexpected perturbations. Thirty-three healthy subjects (17 females, 16 males) were assessed for maximal and explosive isometric knee extension (KE) and plantar flexion (PF) torque and COM response (velocity (COMV), displacement (COMD)) to unexpected platform translations. Relationships between explosive torque and balance measures were investigated using Pearson's correlation and multiple regression. A negative relationship between PF explosive torque at 50, 100, and 150 ms and COMV at 300, 400, and 500 ms (r = -0.363 to -0.508, p ≤ 0.049), and COMD at 400 and 500 ms (r = -0.349 to -0.416, p ≤ 0.046) was revealed. A negative relationship between KE explosive torque at 50, 100, and 150 ms and COMV at 400 ms (r = -0.381 to -0.411, p ≤ 0.029) but not COMD was also revealed. Multiple regression found PF 100 ms predicted 17.3% of variability in COMD at 500 ms and 25.8% of variability in COMV at 400 ms. These results suggest that producing torque rapidly may improve COM response to unexpected perturbation.

Relationships between physical qualities and key performance indicators during match-play in senior international rugby union players

The use of physical tests to profile physical capabilities, and provide training direction to athletes is common practice. Likewise, in professional team sports, notational analysis codes the key contributions of each player during competition. Limited studies have however investigated relationships between physical capabilities and key performance indicators (KPIs) of rugby union match-play. Elite professional players, categorised as forwards (n = 15) or backs (n = 14), from an international rugby union squad (n = 29) undertook assessments of isometric mid-thigh pull (IMTP), bilateral and unilateral countermovement jumps (CMJ) and drop jumps (DJ; from 40 and 20 cm, respectively), and assessment of acceleration (10 m), a 5 m weighted sled drive, and a Yo-Yo intermittent recovery test level 1 (Yo-Yo IRTL1). Game statistics of the same players from 92 matches (~23 matches per player) during the 2014-15 season were analysed for effort and performance-based metrics. For forwards, Yo-Yo IRTL1 correlated significantly with; number of tackles made (r = 0.717), first three players at a ruck in both attack (r = 0.568) and defence (r = 0.581), number of effective rucks (r = 0.630), total possessions (r = 0.522), passes made (r = 0.651), percentage of carries over the gainline (r = 0.610), effective ruck success (r = 0.600), tackle success (r = 0.540), and the number of turnovers made (r = 0.518). Drop jump performance in forwards was associated with; the number of clean breaks (r = 0.558), dominant collisions (r = 0.589), and offloads (r = 0.594). For backs, the sled-drive test correlated with; number of carries (r = -0.751), first three players at an attacking ruck (r = -0.613), effective attacking rucks (r = -0.584), number of dominant collisions (r = -0.792) and offloads (r = -0.814). Likewise, for backs, IMTP peak force was related to; the number of possessions (r = 0.793), passes made (r = 0.792), effective attacking ruck percentage (r = 0.628), and the number of offloads (r = 0.621) whilst relative peak force correlated with; the percentage of carries over the gainline (r = 0.533), percent tackle success (r = 0.603) and effective attacking ruck percentage (r = 0.584). Regression analyses highlighted that only a small number of variables (i.e., carries, tackles, attacking and defensive first three at ruck) returned practically achievable changes (<20%) in physical qualities. In spite of this, and while leaving scope identification of further physical and/or performance predictors, greater strength, power and intermittent running performance were positively related to match-derived KPIs during competition. This may provide a basis for better integrating the strategies used by physical and technical performance-focused coaching staff to improve key performance indicators, and thus match performance, of rugby union players.

A Comparison of the Isometric Midthigh Pull and Isometric Squat: Intraday Reliability, Usefulness, and the Magnitude of Difference Between Tests

PURPOSE

To examine the reliability and usefulness of the isometric midthigh pull (IMTP) and isometric squat (ISqT) performed at the same knee and hip angles. The scores produced in each test were compared to determine the magnitude of differences between tests.

METHODS

Twenty-six male and female athletes (age, 23.6 [4.3] y; height, 1.75 [0.07] m; and body mass, 68.8 [9.7] kg) performed 2 maximal repetitions of the IMTP and ISqT following a specific warm-up.

RESULTS

Maximum force, absolute peak force (PF), relative PF, allometrically scaled PF, rate of force development (0-200 and 0-250 ms), and impulse (0-300 ms) were deemed reliable (intraclass correlation coefficient [ICC] ≥.86 and coefficient of variation [CV] ≤9.4%) in the IMTP and ISqT based on predetermined criteria (ICC ≥.8 and CV ≤10%). Impulse (0-200 and 0-250 ms) was reliable in the ISqT (ICC ≥.92 and CV ≤9.9%). Participants produced significantly (P < .05) greater PF and impulse (0-300 ms) during the ISqT compared with the IMTP. When split by sex, female participants produced significantly greater PF (P = .042) during the ISqT, with no significant differences among male participants (P = .245). Both tests are capable of detecting changes in performance in maximum force and absolute PF.

CONCLUSIONS

Both tests are reliable for non-time-dependent maximal strength measures when measured at the same knee and hip angles. The ISqT may be preferred when coaches want to test an athlete's true maximum lower-limb strength, especially female athletes.

Effect of Different Onset Thresholds on Isometric Midthigh Pull Force-Time Variables

Dos'Santos, T, Jones, PA, Comfort, P, and Thomas, C. Effect of different onset thresholds on isometric midthigh pull force-time variables. J Strength Cond Res 31(12): 3463-3473, 2017-Various thresholds have been used to identify the onset of contraction during isometric midthigh pull (IMTP); however, no agreed onset threshold exists for this assessment. The purpose of this study was to compare relative body weight (BW) and arbitrary onset thresholds to a criterion onset threshold 5 SDs of BW for IMTP force-time variables; force at each threshold, peak force, time-specific force values (100, 150, and 200 ms), and rate of force development (RFD) during 0-100, 0-150, 0-200 ms. Academy rugby league players (n = 9, age: 18.5 ± 0.4 years; height: 1.82 ± 0.09 m; mass: 91.2 ± 13.1 kg) performed 2 IMTP trials on a force platform sampling at 1,000 Hz. The neutral force-time data pool (18 trials) was analyzed with five different thresholds and compared with criterion threshold to determine any variance in force-time variables. Five SDs of BW were significantly lower than 10% BW and 75 N for threshold force which led to significantly greater time-specific force values at 100 and 150 ms and unacceptable limits of agreements (LOA) for all force-time variables. No significant differences (p > 0.05) were observed between 2.5% and 5 SDs of BW; and between 5% and 5 SDs of BW for threshold force and all force-time variables with acceptable LOA. The 5 SDs of BW and 2.5% BW onset thresholds consistently resulted in the lowest values for threshold force, time-specific force values, and RFD, attributed to a lower onset bias. Therefore, scientists and practitioners are recommended to use a 5 SD of BW onset threshold for time-specific force values and RFD for accurate data because it accounts for signal noise during the weighing period. Subsequently, there is greater certainty that the onset of contraction identifies a true meaningful change in force, in contrast to relative BW thresholds.

Knee extension rate of torque development and peak torque: associations with lower extremity function

BACKGROUND

With aging, the ability to generate muscle force decreases, contributing to declines in physical functions such as walking. While most studies assess muscle force by peak torque, the rate of torque development (RTD) reflects a dynamic component of muscle performance that is important for physical function. Using data from the Baltimore Longitudinal Study of Aging, we assessed whether RTD adds significantly to peak torque in associations with lower extremity performance. If so, RTD may help identify weak older adults for screening and intervention.

METHODS

We assessed associations of RTD and peak torque with physical performance independent of demographics, BMI, body composition, and each other in 1089 Baltimore Longitudinal Study of Aging participants (49.7% women; aged 26 to 96 years; women, 64.0 ± 13.8 years; men, 68.4 ± 14.4 years). Peak torque was assessed by isometric and 30 deg/s isokinetic knee extension tests. Peak RTD was operationalized as the maximum torque-time slope among successive 50 ms epochs over the first 3 s of a test of knee extension isometric strength, with the knee joint positioned at 120 deg of flexion. A battery of lower extremity performance tests included gait speed during a 6 m walk at usual and fast pace (6 m usual and fast), time to complete a 400 m walk at fast pace (400 m), distance covered in a 2.5 min walk at normal pace (2.5 min), time to complete 5 and 10 chair stands, and two summary tests of lower extremity performance. Sex-stratified generalized linear regression models were adjusted for age, race, BMI, appendicular lean mass, and whole body fat mass.

RESULTS

In men, independent of either measure of peak torque and cofactors, RTD was a significant (P < 0.05) predictor of all lower extremity performance tests except the 400 m and 2.5 min walks. In women, independent of peak torque, RTD was only a significant independent correlate of the 6 m fast walk (P < 0.001).

CONCLUSIONS

RTD independently contributes to physical functions in men but less in women. The mechanisms underlying the sex difference are unclear and require further study.