Monitoring of in-season neuromuscular and perceptual fatigue in youth rugby players

Monitoring modifiable injury risk factors over an in-season mesocycle in semi-professional female field hockey players

OBJECTIVE

This study aimed to determine changes of modifiable injury risk factors and fatigue parameters during a mesocycle (4 months of the competitive season) in semi-professional female field hockey players (Spanish 2nd Division).

METHODS

Fourteen female field hockey players (age: 22.6 ± 4.9 years) participated in the study over 4 months of the competitive season (September-December 2019). The players were tested each month for their: maximal isometric knee flexion, hip adduction, and abduction muscle strength; passive straight leg raise and ankle dorsiflexion range of motion (ROM); countermovement jump height; and perceptual fatigue (through a perceived well-being questionnaire).

RESULTS

Statistical differences were reported in isometric knee flexion torque in the dominant and non-dominant limb (p = < 0.001, ηp2 = 0.629,0.786 respectively), non-dominant isometric hip abductors torque (p = 0.016, ηp2 = 0.266) and isometric hip adductors torque in dominant and non-dominant limbs (p = < 0.001, ηp2 = 0.441-546). Also, significant differences were reported in the straight leg raise test (p = < 0.001, ηp2 = 0-523, 0.556) and ankle dorsiflexion (p = 0.001, ηp2 = 0.376, 0.377) for the dominant and non-dominant limb respectively. Finally, the jump height measured showed significant differences (p = <.001, ηp2 = 0.490), while no differences were reported in perceived well-being parameters (p = 0.089-0.459).

CONCLUSION

Increments in isometric muscle strength and fluctuations in ROM values and vertical jumping capacity are reported over an in-season mesocycle (i.e., 4 months of the competitive season). This information can be used to target recovery strategies to make them more efficient.

New Zealand Youth Rugby Sevens: A Comparative Match Demands Study

Rugby sevens has established itself on the world stage since its inclusion in the 2016 Olympics. Participation among New Zealand (NZ) youth has surged. Sevens games have specific high demands, but little is known about these competitive demands in regards to youth. Two NZ male youth squads (U15, n = 13; U19, n = 14) were monitored during a national sevens tournament. Microsensor technology captured heart rate (HR) and kinematic performance. The rating of perceived exertion (RPE) was collected for U15 matches only. U19 and U15 players ran 108 ± 11 and 116 ± 13 m·min^-1 at an average speed (V_AVG) of 6.5 ± 0.6 and 6.9 ± 0.8 km·h^-1. Peak speeds (V_PEAK) reached 33.7 km·h^-1, and high-intensity running distance (HIRD) averaged 252 ± 102 m. U15 (44.3 ± 9.2 game^-1) and U19 (39.4 ± 6.1 game^-1) showed different sprint rates. U15 covered more moderate-velocity distance (20-80% V_MAX) and less low-velocity distance (<20% V_MAX). RPE was 13 ± 1 (U15). An average HR of 90.0 ± 3.9% HR_MAX was recorded. Upwards of 57% of game time was played at >95% HR_MAX. Youth sevens competition is specifically demanding. U15 can experience greater loads than older peers in rugby. Coaches can use this information to optimize players' physical development.

The Effects of Soccer Specific Exercise on Countermovement Jump Performance in Elite Youth Soccer Players

The aims of the study were to examine the test−retest reliability of force-time (F-T) characteristics and F-T curve waveform of bilateral and unilateral countermovement jumps (CMJ) in elite youth soccer players and to evaluate the effects of competitive match-play on CMJ performance. 16 male youth soccer players completed CMJs on two separate occasions to determine reliability, and immediately pre, post and 48 h following a competitive match. Coefficient of variation (CV%), Intra-class correlation coefficient (ICC) and limits of agreement were used to assess reliability of discreate CMJ variables. Single factor repeated measures ANOVA were used to determine the effects of match play. Statistical parametric mapping was used to evaluate the repeatability of the CMJ force-time waveform and the effects of match play. Jump height had limited reliability in all three jumps and only a select few jump specific F-T variables were found to be reliable (CV < 10%, ICC > 0.5). Select variables were reduced immediately post game but recovered 48 h post game. The F-T curve waveform was found to be repeatable but did not differ following match-play. This study suggest that select F-T variables change following match-play and may be suitable tools to allow practitioners to detect decrements in performance. These data may help inform practitioners to use the most appropriate F-T variables to assess fatigue and recovery, with implications for performance and injury risk.

Changes in body composition and physical performance measures during a regular competitive season among young backs and forwards rugby players

This study aimed to compare the changes in body composition and physical qualities of under 19's backs and forwards during the season (i.e. from pre-season [Pre-S] to end-season [End-S]). Twenty-seven male youth rugby union players (mean ± SD: age, Forwards [n = 11]: 17.5 ± 1.2 and Backs [n = 16]: 17.0 ± 0.9 years) participated in this study. Participants were tested twice (i.e. at Pre-S and End-S) and completed: anthropometric, body composition, countermovement and squat jumps, 30-m sprint, squat and bench press 1-repetition maximum (SQ-1RM and BP-1RM). Significant differences were observed between Pre-S and End-S for body mass (BM) and lean mass (LM), among both playing positions (p < 0.034; ES > 0.71), whereas all other variables remained unchanged. Regarding physical performance, backs and forwards showed greater SQ-1RM and BP-1RM, respectively (p < 0.043; ES>-0.69). Moreover, backs and forwards exhibited higher split times from 5 to 30 m (p: 0.013 to <0.001). Substantial increases were observed in BM and LM for backs and forwards, which may have negatively impacted acceleration (i.e. 5-m sprint time) and initial sprint momentum for both playing positions. Our findings highlight the importance of carefully balancing changes in BM and body composition, to avoiding the detrimental effects of these variations on sprint performance.

A Systematic Review on Fitness Testing in Adult Male Basketball Players: Tests Adopted, Characteristics Reported and Recommendations for Practice

Background

As basketball match-play requires players to possess a wide range of physical characteristics, many tests have been introduced in the literature to identify talent and quantify fitness in various samples of players. However, a synthesis of the literature to identify the most frequently used tests, outcome variables, and normative values for basketball-related physical characteristics in adult male basketball players is yet to be conducted.

Objective

The primary objectives of this systematic review are to (1) identify tests and outcome variables used to assess physical characteristics in adult male basketball players across all competition levels, (2) report a summary of anthropometric, muscular power, linear speed, change-of-direction speed, agility, strength, anaerobic capacity, and aerobic capacity in adult male basketball players based on playing position and competition level, and (3) introduce a framework outlining recommended testing approaches to quantify physical characteristics in adult male basketball players.

Methods

A systematic review of MEDLINE, PubMed, SPORTDiscus, Scopus, and Web of Science was performed following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines to identify relevant studies. To be eligible for inclusion, studies were required to: (1) be original research articles; (2) be published in a peer-reviewed journal; (3) have full-text versions available in the English language; and (4) include the primary aim of reporting tests used and/or the physical characteristics of adult (i.e., ≥ 18 years of age) male basketball players. Additionally, data from the top 10 draft picks who participated in the National Basketball Association combined from 2011–12 to 2020–21 were extracted from the official league website to highlight the physical characteristics of elite 19- to 24-year-old basketball players.

Results

A total of 1684 studies were identified, with 375 being duplicates. Consequently, the titles and abstracts of 1309 studies were screened and 231 studies were eligible for full-text review. The reference list of each study was searched, with a further 59 studies identified as eligible for review. After full-text screening, 137 studies identified tests, while 114 studies reported physical characteristics in adult male basketball players.

Conclusions

Physical characteristics reported indicate a wide range of abilities are present across playing competitions. The tests and outcome variables reported in the literature highlight the multitude of tests currently being used. Because there are no accepted international standards for physical assessment of basketball players, establishing normative data is challenging. Therefore, future testing should involve repeatable protocols that are standardised and provide outcomes that can be monitored across time. Recommendations for testing batteries in adult male basketball players are provided so improved interpretation of data can occur.

Clinical Trial Registration

This review was registered with the International Prospective Register of Systematic Reviews and allocated registration number CRD42020187151 on 28 April, 2020.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40279-021-01626-3.

Effect of Cycling Cadence on Neuromuscular Function: A Systematic Review of Acute and Chronic Alterations

There is a wide range of cadence available to cyclists to produce power, yet they choose to pedal across a narrow one. While neuromuscular alterations during a pedaling bout at non-preferred cadences were previously reviewed, modifications subsequent to one fatiguing session or training intervention have not been focused on. We performed a systematic literature search of PubMed and Web of Science up to the end of 2020. Thirteen relevant articles were identified, among which eleven focused on fatigability and two on training intervention. Cadences were mainly defined as “low” and “high” compared with a range of freely chosen cadences for given power output. However, the heterogeneity of selected cadences, neuromuscular assessment methodology, and selected population makes the comparison between the studies complicated. Even though cycling at a high cadence and high intensity impaired more neuromuscular function and performance than low-cadence cycling, it remains unclear if cycling cadence plays a role in the onset of fatigue. Research concerning the effect of training at non-preferred cadences on neuromuscular adaptation allows us to encourage the use of various training stimuli but not to say whether a range of cadences favors subsequent neuromuscular performance.

Intra- and Inter-week Variations of Well-Being Across a Season: A Cohort Study in Elite Youth Male Soccer Players

This study describes the weekly variations of well-being ratings relative to fatigue (wFatigue), stress (wStress), delayed-onset muscle soreness (wDOMS), sleep quality (wSleep), and Hooper questionnaire (wHQ) throughout the season. In addition, the well-being variables for the playing position in different moments of the season were discussed. Twenty-one elite young soccer players U17 took part in this study. From the beginning of the pre-season, well-being status was monitored daily by the HQ method throughout 36 weeks, including four periods: (1) pre-season, (2) early-season, (3) mid-season, and (4) end-season. Players trained at least 3 times per week throughout the season. The main outcome was that, in weeks 33 and 28, the highest [wFatigue: 15.85 ± 3.38 arbitrary units (AU); wHQ: 48.86 ± 9.23 AU] and the lowest (wFatigue: 5.38 ± 1.88 AU; wHQ: 20.43 ± 5.49 AU) wFatigue and wHQ occurred, respectively, although the lowest level of wDOMS happened in week 28 (4.86 ± 2.15 AU), while the highest wDOMS was observed in week 5 (14.65 ± 4.16 AU). The highest wSleep (13.00 ± 2.12 AU) and wStress (11.65 ± 2.92 AU) were observed in weeks 8 and 34, respectively, while the lowest wSleep (5.81 ± 2.29 AU) and wStress (3.76 ± 0.94 AU) were marked in week 29 coincidentally. In the HQ between every weekday, except recovery day, and the day of the match (MD), considerable highest HQ was only revealed in 2 days after MD in contrast to overall team comparison. In the present study, we observed that the well-being changes between different phases of the season as well as between weeks and days of the week with the MD are significant. These results provide a great point of view for coaches and practitioners about well-being variations over a season in elite youth soccer level. As a result, coaches will be more aware about non-functional overreaching and taking measures to prevent it.

The Influence of Age and Maturation on Trajectories of Stretch-Shortening Cycle Capability in Male Youth Team Sports

PURPOSE

To examine the influence of growth and maturation in the trajectory of stretch-shortening cycle capability.

METHOD

Using a mixed-longitudinal design, absolute and relative leg stiffness and reactive strength index (RSI) were measured 3 times over a 3-year period in 44 youth team-sport players. Maturation was determined as maturity offset and included within the Bayesian inference analysis as a covariate alongside chronological age.

RESULTS

Irrespective of age and maturation, there was no change in absolute leg stiffness, however relative leg stiffness decreased over time. Maturation and age reduced this decline, but the decline remained significant (Bayesian factor [10] = 5097, model averaged R2 = .61). The RSI increased over time and more so in older more mature youth players (Bayesian factor [10] = 9.29e8, model averaged R2 = .657).

CONCLUSION

In youth players who are at/post peak height velocity, relative leg stiffness appears to decline, which could have an impact on both performance and injury risk. However, RSI increases during this period, and these data reinforce that leg stiffness and RSI reflect different components of stretch-shortening cycle capability. Practitioners should consider these differences when planning training to maximize stretch-shortening cycle capability during growth and maturation in athletes on the developmental performance pathway.

Gaelic Football Match-Play: Performance Attenuation and Timeline of Recovery

This study investigated acute changes in markers of fatigue and performance attenuation during and following a competitive senior club-level Gaelic football match. Forty-one players were tested immediately pre-match, at half-time, full-time, 24 h post-match and 48 h post-match. Creatine kinase, drop jump height and contact-time, reactive strength index, countermovement jump height and perceptual responses were assessed at the aforementioned time-points. 18 Hz global positioning system devices were used to record players in-game workload measures. Compared to pre-match, perceptual responses (−27.6%) and countermovement jump height (−3.9%) were significantly reduced at full-time (p < 0.05). Drop jump height (−8.8%), perceptual responses (−27.6%), reactive strength index (−15.6%) and countermovement jump height (−8.6%) were significantly lower 24 h post-match (p < 0.05). Pre-match creatine kinase was significantly increased (+16.2% to +159.9%) when compared to all other time-points (p < 0.05). Total distance, total accelerations, total sprints, sprint distance and average heart rate were all correlated to changes in perceptual responses (r = 0.34 to 0.56, p < 0.05). Additionally, maximum speed achieved (r = 0.34) and sprint distance (r = 0.31) were significantly related to countermovement jump changes (p < 0.05), while impacts (r = 0.36) were correlated to creatine kinase increases (p < 0.05). These results demonstrate that Gaelic football match-play elicits substantial neuromuscular, biochemical and perceptual disturbances.

The moderating impact of maturation on acute neuromuscular and psycho-physiological responses to simulated soccer activity in academy soccer players

AbstractResource constraints complicate load monitoring practices in some academies, which is problematic based on load-injury associations surrounding periods of rapid non-linear growth. Limited research has explored relationships between maturation and perceived psycho-physiological response to activity and associated neuromuscular performance changes. This study aimed to quantify neuromuscular and psycho-physiological responses to standardised activity and analyse whether dose-responses were moderated by maturation. Fifty-seven male soccer players (age: 14.1 ± 0.9 years; stature: 165 ± 10 cm; body mass, 57 ± 9 kg; percentage of predicted adult height 92.7 ± 5%) from two Elite Player Performance Plan (EPPP) academies completed the youth soccer-specific aerobic fitness test (Y-SAFT⁶⁰). Countermovement jump (CMJ), reactive strength index (RSI), absolute (ABS) and relative leg stiffness (REL) were measured pre-post the Y-SAFT⁶⁰ with playerload (PL), heart rate (HR), total distance (TD^ist) and differential ratings of perceived exertion (dRPE) used as markers of load and intensity. A moderation model was employed to analyse interactions of maturation as a continuous variable. Analysis indicated no significant interaction (p <0.05) between maturation and neuromuscular performance but RPE-Technical demonstrated significant interactions (p = 0.01). Slope analysis indicated four variables (PL, RSI, ABS and REL) that demonstrated significance at various stages of maturation, most notably aligning with peak height velocity (∼87-96% PAH). Tentatively, we propose that maturational developments in the neuromuscular system offer some mechanistic explanation to the varied dose-responses observed. It is therefore important that maturation is habitually considered within prescription of training programmes and that further empirical studies are completed to determine maturity specific dose-responses.Highlights Components of both neuromuscular performance and psycho-physiological response to simulated soccer was influenced by maturity status.Individuals more biologically developed are more capable of 'coping' with the biomechanical load of simulated soccer activity resulting in more favourable neuromuscular responses.The period surrounding peak height velocity appears to influence whole body load-response pathways resulting in altered movement patterns during this period.To minimise the impact of maturity status, practitioners can restrict activities that elicit high biomechanical load and introduce biologically categorised training activities.

Athlete-Reported Outcome Measures for Monitoring Training Responses: A Systematic Review of Risk of Bias and Measurement Property Quality According to the COSMIN Guidelines

BACKGROUND

Athlete-reported outcome measures (AROMs) are frequently used in research and practice but no studies have examined their psychometric properties.

OBJECTIVES

Part 1-identify the most commonly used AROMs in sport for monitoring training responses; part 2-assess risk of bias, measurement properties, and level of evidence, based on the COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) guidelines.

STUDY APPRAISAL AND SYNTHESIS METHODS

Methodological quality of the studies, quality of measurement properties, and level of evidence were determined using the COSMIN checklist and criteria.

RESULTS

Part 1-from 9446 articles screened for title and abstract, 310 out of 334 full texts were included; 53.9% of the AROMs contained multiple items, while 46.1% contained single items. Part 2-from 1895 articles screened for title and abstract, 71 were selected. Most measurement properties of multiple-item AROMs were adequate, but content validity and measurement error were inadequate. With the exclusion of 2 studies examining reliability and responsiveness, no validity studies were found for single items.

CONCLUSIONS

The measurement properties of multiple-item AROMs derived from psychometrics were acceptable (with the exclusion of content validity and measurement error). The single-item AROMs most frequently used in sport science have not been validated. Additionally, nonvalidated modified versions of the originally nonvalidated items are common. Until proper validation studies are completed, all conclusions based on these AROMs are questionable. Established reference methods, such as those of clinimetrics, should be used to develop and assess the validity of AROMs.

Convergent Validity, Reliability, and Sensitivity of a Running Test to Monitor Neuromuscular Fatigue

PURPOSE

To investigate the convergent validity, reliability, and sensitivity over a week of training of a standardized running test to measure neuromuscular fatigue.

METHODS

Twenty male rugby union players were recruited for the study, which took place during preseason. The standardized running test consisted of four 60-m runs paced at  ~5 m·s-1 with 33 seconds of recovery between trials. Data from micromechanical electrical systems were used to calculate a running-load index (RLI), which was a ratio between the mechanical load and the speed performed during runs. RLI was calculated by using either the entire duration of the run or a constant-velocity period. For each type of calculation, either an individual directional or the sum of the 3 components of the accelerometer was used. A measure of leg stiffness was used to assess the convergent validity of the RLI.

RESULTS

Unclear to large relationships between leg stiffness and RLI were found (r ranged from -.20 to .62). Regarding reliability, small to moderate (.47-.86) standardized typical errors were found. The sensitivity analysis showed that the leg stiffness presented a very likely trivial change over the course of 1 week of training, whereas RLI showed very likely small to a most likely large change.

CONCLUSIONS

This study showed that RLI is a practical method to measure neuromuscular fatigue. In addition, such a methodology aligns with the constraint of elite team-sport setup due to its ease of implementation in practice.

Lower Extremity Stiffness in Collegiate Distance Runners Pre- and Post-Competition

Previous evidence has suggested that there is a relationship between leg stiffness and improved running performance. The purpose of this investigation was to determine how leg stiffness of runners was influenced in the 24 and 48 hour period following a cross country race. Twenty-two collegiate cross-country runners (13 males, 9 females, 19.5 ± 1.4 yr) were recruited and participated in the study. Leg stiffness was assessed 24 hours before and after a race as well as 48 hours post-race. Three jumping protocols were conducted: 1) a static jump, 2) a countermovement jump, and 3) a vertical hopping test. Two embedded force plates (1000 Hz) were utilized to measure ground reaction forces for each test and a metronome was utilized to maintain hopping frequency (2.2 Hz). A significant main effect was found for a static jump, a countermovement jump and leg stiffness. Leg stiffness was significantly reduced 24 hours post-race (pre-race 36.84 kN·m^-1, 24h post 33.11 kN·m^-1, p < 0.05), but not 48 hours post-race (36.30 kN·m^-1). No significant differences were found in post-hoc analysis for the squat jump, countermovement jump height and the eccentric utilization ratio. Following a cross-country race, leg stiffness significantly declined in a group of collegiate runners in the immediate 24 hours post-race, but returned to baseline 48 hours post-race. Sport scientists and running coaches may be able to monitor leg stiffness as a metric to properly prescribe training regiments.

Applied Sport Science for Male Age-Grade Rugby Union in England

Rugby union (RU) is a skill-collision team sport played at junior and senior levels worldwide. Within England, age-grade rugby governs the participation and talent development of youth players. The RU player development pathway has recently been questioned, regarding player performance and well-being, which sport science research can address. The purpose of this review was to summarise and critically appraise the literature in relation to the applied sport science of male age-grade RU players in England focussing upon (1) match-play characteristics, (2) training exposures, (3) physical qualities, (4) fatigue and recovery, (5) nutrition, (6) psychological challenges and development, and (7) injury. Current research evidence suggests that age, playing level and position influence the match-play characteristics of age-grade RU. Training exposures of players are described as 'organised chaos' due to the multiple environments and stakeholders involved in coordinating training schedules. Fatigue is apparent up to 72 h post match-play. Well-developed physical qualities are important for player development and injury risk reduction. The nutritional requirements are high due to the energetic costs of collisions. Concerns around the psychological characteristics have also been identified (e.g. perfectionism). Injury risk is an important consideration with prevention strategies available. This review highlights the important multi-disciplinary aspects of sport science for developing age-grade RU players for continued participation and player development. The review describes where some current practices may not be optimal, provides a framework to assist practitioners to effectively prepare age-grade players for the holistic demands of youth RU and considers areas for future research.

A Review of Countermovement and Squat Jump Testing Methods in the Context of Public Health Examination in Adolescence: Reliability and Feasibility of Current Testing Procedures

BACKGROUND

In the context of a public health physical fitness (PF) examination in adolescence, a countermovement jump (CMJ) and a squat jump (SJ) are two vertical jump (VJ) tests widely used to evaluate lower limb muscle strength and power, respectively. The main criticism of both the CMJ and SJ test is the lack of test standardization. Therefore, the objectives of this review are: (a) to gather information about both jumps; (b) to investigate whether it is possible to identify common procedures referred to in the CMJ and SJ technical execution, and (c) to design standard operating procedures (SOPs) to promote CMJ and SJ standardization in an adolescent population aged 12-18 years.

METHODS

The review partially adopted the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Statement (PRISMA). Due to growing attention in monitoring physical health through field tests in recent years, articles were collected using the PubMed, Web of Science, and Scopus databases from January 2009 to July 2019. Original articles in which CMJ or SJ were used to assess the muscular strength in adolescents were eligible for further analysis. Articles written in English was imposed as a limit.

RESULTS

A total of 117 studies met the inclusion criteria. The description of the CMJ and SJ test procedures was different within the literature, with discrepancies in the jump technique, number of jumps, and measurement devices used.

CONCLUSIONS

A lack of method standardization for both the CMJ and the SJ test was identified. Based on the literature, SOPs for both VJs were proposed. These are useful in the context of public health PF examination in adolescents, as they facilitate an unbiased comparison of jump performance data between published studies.

Monitoring residual 36 h post-match neuromuscular fatigue in rugby union; a role for postural control?

The present study investigated single-leg balance and landing measures, respectively, at the beginning of a weekly micro-cycle 36 h after a match compared to 48 h rest without any match load. Twenty-seven professional rugby union players performed balance and landing tests on a 1000 Hz force plate across three in-season micro-cycles either with or without match loads in the prior 36 h. Participants were further sub-divided into higher and lower match load groups to investigate changes in balance and landing variables. Differences between rested and 36 h post-match single-leg balance sway velocity were trivial in all cases, except for the higher-load group on the dominant leg, which were possibly impaired 36 h post-match (ES ± 90% CL = 0.68 ± 0.66). Differences between rested and 36 h post-match single-leg landing measures of relative impulse on the non-dominant leg were possibly lower (0.36 ± 0.34), with possible impairment observed on both legs in the higher load group 36 h post-match (0.39 ± 0.33; 0.49 ± 0.42). Differences in landing measures of peak force and time to stabilisation were mainly trivial (ES < 0.20). Postural control measures at 36 h post-match are comparable to a rested state; though impairment of sway velocity on the dominant leg and landing impulse may indicate residual neuromuscular fatigue resulting from increased match exposure.

Training Loads and RSA and Aerobic Performance Changes During the Preseason in Youth Soccer Squads

The aims of this study were to compare the internal training load (ITL) in soccer players of two competitive age groups (under-15 [U-15] and under-19 [U-19]) during an 8-week preseason training period and compare the associated changes in physical performance measures. Eighteen U-15 and twelve U-19 players were monitored over an 8-week period during the preseason phase. The ITL was monitored using the session rating of perceived exertion (RPE) method. Before and after the preseason period, physical performance was assessed by best (RSA_best) and mean (RSA_mean) times in a repeated sprint ability (RSA) test and peak velocity derived from the Carminatti test (PVT-CAR). Total weekly ITL increased with age (U-15: 13770 ± 874 AU vs. U-19: 33584 ± 2506 AU; p < 0.001). In addition, U-19 players perceived training sessions as heavier than U-15 players (6.1 ± 0.3 vs. 5.3 ± 0.3 AU, respectively; p < 0.001). After the preseason period, very likely to almost certainly positive changes were observed for all performance measures in both age groups. However, the U-15 group had possibly superior gains in RSA_best (+1.40%, 90%CL -0.29 to 3.05, with ES = 0.35) and likely higher effects in RSA_mean (+1.89%, 90%CL 0.04 to 3.70, with ES = 0.53) and PV_T-CAR (+2.71%, 90%CL 0.35 to 5.01, with ES = 0.37) compared to the U-19 group. In conclusion, our findings demonstrate that the U-19 group accumulate higher total weekly ITLs than the U-15 group during the preseason phase due to longer and heavier training sessions. However, the U-15 group obtained superior gains in soccer-specific physical abilities while accumulating half the total ITLs during lighter training sessions.

Creatine kinase, neuromuscular fatigue, and the contact codes of football: A systematic review and meta-analysis of pre- and post-match differences

Physiological or performance tests are routinely utilised to assess athletes' recovery. At present, the ideal tool to assess recovery remains unknown. Therefore, the aim of this systematic review was to examine the change in creatine kinase (CK) and neuromuscular function as measured via a countermovement jump (CMJ) following a match in the contact codes of football. A comprehensive search of databases was undertaken with RevMan (V 5.3) used for statistical analysis. Our results demonstrated that CK pre- versus post-match (standardised mean difference (SMD) = 0.90, 95% CI = 0.50 to 1.31, p < .0001), CK pre- versus 24 h post-match (SMD = 1.50, 95% CI = 1.12 to 1.88, p < .00001), and CK pre- versus 48 h post-match all increased significantly (SMD = 0.90, 95% CI = 0.50 to 1.31, p < .0001), while CMJ peak power (PP) pre- versus post-match (SMD = -0.59, 95% CI = -1.12 to -0.06, p = .03), and pre- versus 24 h post-match (SMD = -0.80, 95% CI = -1.31 to -0.28, p = .002) decreased significantly. There was a significant relationship between the change in CK and the change in CMJ PP from immediately pre to immediately post (r = -0.924, p = .025), and between CMJ immediately following a match and 24 h CK change (r = -0.983, p = .017). In conclusion, CK levels increase and performance in the CMJ decreases following a match of a contact code of football. The identification of this relationship may allow coaching staff to implement a standalone measure of recovery.

The effects of short term detraining and retraining on physical fitness in elite soccer players

Purpose

The aim of this study was to examine the effects of aerobic high-intensity training with reduced volume and training cessation on body composition and physical fitness after the end of season and the time required to recapture physical fitness with intensified retraining following two weeks of detraining in elite soccer players.

Method

Twenty male semi-professional soccer players participated in this study. The soccer players were assigned to either a group that completed high-intensity aerobic training (HAT, n = 10) or to a detraining and retraining group (DHAT, n = 10) for a 5-week period immediately after the end of the season. The first 2 weeks of the period, members of the HAT group performed high-intensity aerobic exercise (80–90% of HRmax, 12 min × 3, three times per week), whereas members of the DHAT group abstained from any physical activity. During the subsequent 3 weeks, members of both the HAT and DHAT groups completed high-intensity aerobic exercise. Exercise performance testing and body composition analysis were performed before; after 2 weeks of detraining; and at 1, 2 and 3 weeks of retraining.

Results

Intensified high-intensity training for 5 weeks maintained the performance in the Yo-Yo Intermittent Recovery level 2 test (Yo-Yo IR2) and repeated sprints at any time point (P > 0.05). However 2 weeks of detraining resulted in significant decreases in the performance on the Yo-Yo IR2 (P < 0.01) and repeated sprints test (P < 0.05). Performance on the Yo-Yo IR2 enhanced after 2 weeks of retraining and was maintained up to 3 weeks after retraining, with no significant differences between conditions (P > 0.05). In addition, repeated sprint performance markedly decreased after the detraining period (P < 0.05) and was continuously lower compared to the baseline at 2 weeks after retraining (P < 0.05). Furthermore, this value reached baseline level at the end of the experimental period (P > 0.05). There were no significant differences between conditions in body composition, performance of agility, or sprint ability throughout the 5-week experimental period (P > 0.05).

Conclusions

The present data suggest that short-term detraining after the competitive season can markedly decrease performances in the Yo-Yo IR2 test and repeated sprints. To return to a previous level of ability on the Yo-Yo IR2 and/or sprint test with retraining through high-intensity aerobic training after a period of detraining, a similar or longer period of retraining is required. However, the high-intensity training with reduced amount of training after competitive season can prevent reductions in physical fitness.

Validity and Usability of a New System for Measuring and Monitoring Variations in Vertical Jump Performance

Loturco, I, Pereira, LA, Kobal, R, Kitamura, K, Cal Abad, CC, Marques, G, Guerriero, A, Moraes, JE, and Nakamura, FY. Validity and usability of a new system for measuring and monitoring variations in vertical jump performance. J Strength Cond Res 31(9): 2579-2585, 2017-Vertical jump (VJ) height is one of the most sensitive measures to quantify training-related fatigue and athletic performance in elite athletes. Currently, however, there is no equipment designed to graphically deliver the daily performance changes in VJ compared with the smallest worthwhile change (SWC), which is considered essential in "progressive statistics" to judge meaningful performance fluctuations. The aims of the study were to analyze the criterion validity of a new contact mat (i.e., Elite Jump), alongside testing its usability to detect meaningful changes in VJ of elite team sport athletes. A total of 31 athletes participated in the criterion validity part of the study, whereas 17 rugby players participated in the VJ sensitivity part. When compared with the force plate, the contact mat produced squat jump (SJ) and countermovement jump (CMJ) values with very high intraclass correlation coefficients (0.998 and 0.997, respectively) and very low biases (-0.11 and -0.08 cm, respectively), as assessed by the Bland-Altman plot. In addition, during a training microcycle, rugby players presented identical meaningful changes in performance in both SJ and CMJ when comparing the Elite Jump and Hopkins' spreadsheet outputs. Therefore, the contact mat is valid and the proprietary software can properly execute the SWC calculations, providing coaches and researchers with accurate information concerning variations in the physical performance of elite athletes.

Effects of Two Different Volume-Equated Weekly Distributed Short-Term Plyometric Training Programs on Futsal Players' Physical Performance

Yanci, J, Castillo, D, Iturricastillo, A, Ayarra, R, and Nakamura, FY. Effects of two different volume-equated weekly distributed short-term plyometric training programs on futsal players' physical performance. J Strength Cond Res 31(7): 1787-1794, 2017-The aim was to analyze the effect of 2 different plyometric training programs (i.e., 1 vs. 2 sessions per week, same total weekly volume) on physical performance in futsal players. Forty-four futsal players were divided into 3 training groups differing in weekly plyometric training load: the 2 days per week plyometric training group (PT2D, n = 15), the 1 day per week plyometric training group (PT1D, n = 12), and the control group (CG, n = 12) which did not perform plyometric training. The results of this study showed that in-season futsal training per se was capable of improving repeat sprint ability (RSA) (effect size [ES] = -0.59 to -1.53). However, while change of direction ability (CODA) was maintained during the training period (ES = 0.00), 15-m sprint (ES = 0.73), and vertical jump (VJ) performance (ES = -0.30 to -1.37) were significantly impaired. By contrast, PT2D and PT1D plyometric training were effective in improving futsal players' 15-m sprint (ES = -0.64 to -1.00), CODA (ES = -1.83 to -5.50), and horizontal jump (ES = 0.33-0.64) performance. Nonetheless, all groups (i.e., PT2D, PT1D, and CG) presented a reduction in VJ performance (ES = -0.04 to -1.37). Regarding RSA performance, PT1D showed a similar improvement compared with CG (ES = -0.65 to -1.53) after the training intervention, whereas PT2D did not show significant change (ES = -0.04 to -0.38). These results may have considerable practical relevance for the optimal design of plyometric training programs for futsal players, given that a 1-day-per-week plyometric training program is more efficient than a 2-day-per-week plyometric training program to improve the futsal players' physical performance.

Variability of Jump Kinetics Related to Training Load in Elite Female Basketball

The purpose of this study was to quantify changes in jump performance and variability in elite female basketballers. Junior and senior female representative basketball players (n = 10) aged 18 ± 2 years participated in this study. Countermovement jump (CMJ) data was collected with a Gymaware™ optical encoder at pre-, mid-, and post-season time points across 10 weeks. Jump performance was maintained across the course of the full season (from pre to post). Concentric peak velocity, jump height, and dip showed the most stability from pre- to post-season, with the %CV ranging from 5.6⁻8.9%. In the period of the highest training load (mid-season), the variability of within-subject performance was reduced by approximately 2⁻4% in all measures except for jump height. Altered jump mechanics through a small (0.26 effect size) increase in dip were evident at mid-season, suggesting that CMJ analysis is useful for coaches to use as an in-season monitoring tool. The highest coefficient of variation (8⁻22%CV) in inter-set scores in all measures except eccentric peak velocity also occurred mid-season. It appears that in-season load not only impairs jump performance, but also movement variability in basketball players.

A Review of the Anthropometric Characteristics, Grading and Dispensation of Junior and Youth Rugby Union Players in Australia

The grading of Australian junior and youth rugby union players has received substantial media attention in recent years. Media reports have focussed on size mismatches observed between players, especially players with Polynesian heritage, and the concerned parents who fear for the safety of their child owing to perceived mismatches. Although such concerns are well meaning, few media reports recognise the need for substantial evidence to determine the best grading system for junior and youth rugby union players. The current study reviewed relevant literature pertinent to the grading and dispensation of junior and youth rugby union players. Using primary and secondary search strategies, a total of 33 articles reporting the anthropometric characteristics of junior and youth rugby players were identified. Anthropometric data from the literature were compared with normative population data and currently used dispensation criteria. Junior and youth rugby players were found to be taller and heavier than normative population data. Current dispensation criteria, in terms of body mass, were found to vary and it is suggested that criteria be revised and standardised across rugby unions throughout Australia. Although it is acknowledged that other factors are important for grading players, anthropometric characteristics should be considered as potential dispensation criteria to supplement current age-based grading for junior and youth rugby union players. Measuring the body mass and stature of each junior player upon pre-season registration is suggested, which would provide data to establish valid dispensation criteria for the following season.

National Strength and Conditioning Association Position Statement on Long-Term Athletic Development

There has recently been a growing interest in long-term athletic development for youth. Because of their unique physical, psychological, and social differences, children and adolescents should engage in appropriately prescribed exercise programs that promote physical development to prevent injury and enhance fitness behaviors that can be retained later in life. Irrespective of whether a child is involved in organized sport or engages in recreational physical activity, there remains a need to adopt a structured, logical, and evidence-based approach to the long-term development of athleticism. This is of particular importance considering the alarmingly high number of youth who fail to meet global physical activity recommendations and consequently present with negative health profiles. However, appropriate exercise prescription is also crucial for those young athletes who are physically underprepared and at risk of overuse injury because of high volumes of competition and an absence of preparatory conditioning. Whether the child accumulates insufficient or excessive amounts of exercise, or falls somewhere between these opposing ends of the spectrum, it is generally accepted that the young bodies of modern day youth are often ill-prepared to tolerate the rigors of sports or physical activity. All youth should engage in regular physical activity and thus should be viewed as "athletes" and afforded the opportunity to enhance athleticism in an individualized, holistic, and child-centered manner. Because of emerging interest in long-term athletic development, an authorship team was tasked on behalf of the National Strength and Conditioning Association (NSCA) to critically synthesize existing literature and current practices within the field and to compose a relevant position statement. This document was subsequently reviewed and formally ratified by the NSCA Board of Directors. A list of 10 pillars of successful long-term athletic development are presented, which summarize the key recommendations detailed within the position statement. With these pillars in place, it is believed that the NSCA can (a) help foster a more unified and holistic approach to long-term athletic development, (b) promote the benefits of a lifetime of healthy physical activity, and