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Hamstring injuries constitute the single largest cause of lost playing time in professional football. While restoring high-speed running ability is paramount for rehabilitation from these injuries, little evidence exists regarding the extent of return to sport running performance after hamstring injury in football. We examined medical and match performance data available from a sample of 38 professional soccer players competing in the Qatar Stars League (N = 1426 observations) to describe high-speed running performance during match-play prior and subsequent to a hamstring strain injury. Multivariable-adjusted random-effects generalized additive models estimated post- versus pre-hamstring injury differences in maximal speed (km/h), high-speed running (>20 km/h), and sprinting (>25 km/h) distance. Mean effects and uncertainty (95% confidence interval, CI) were interpreted against the estimated random match-to-match variability in maximal sprinting speed, high-speed running distance, and sprinting running distance of ±1.67 km/h (95% CI, 1.62-1.72 km/h), ±102 m (95% CI, 99-105 m), and ±60 m (95% CI, 58-61 m), respectively. The estimated post- versus pre-hamstring injury mean differences in maximal sprinting speed, high-speed running distance, and sprinting running distance primary outcomes were -0.25 km/h (95% CI, -0.38 to -0.12 km/h), -43 m (95% CI, -56 to -30 m), and -22 m (95% CI, -29 to -16 m). Players returning to football match-play after hamstring strain injury experienced reductions in high-speed match physical performance that were well within normal match-to-match variation in performance.

This study aimed to explore the influence of differences in relative skeletal maturity on performance test outcomes in elite youth soccer players from the Middle East.We integrated skeletal age and performance assessments using mixed-longitudinal data available for 199 outfield players (chronological age range, 11.7 to 17.8 yr) enrolled as academy student-athletes (annual screening range, 1 to 5 visits). Skeletal age was determined as per the Tanner-Whitehouse II protocol. Relative maturity was calculated as the difference (∆) between Tanner-Whitehouse II skeletal age minus chronological age. Performance test outcomes of interest were 10-m sprinting, 40-m sprinting, countermovement jump height, and maximal aerobic speed. Separate random-effects generalized additive models quantified differences in performance test outcomes by relative skeletal maturity. Estimated differences were deemed practically relevant based on the location of the confidence interval (95% CI) against minimal detectable change values for each performance test outcome.For 40-m sprinting, differences of +0.51 s (95% CI, +0.35 to +0.67 s) and +0.62 s (95% CI, +0.45 to +0.78 s) were practically relevant for relative maturity status of ∆ = -1.5 yr versus ∆ = +0.5 and ∆ = +1 yr, respectively. For countermovement jump height, a difference of -8 cm (95% CI, -10 to -5 cm) was practically relevant for ∆ = -1.5 yr versus ∆ = +1 yr relative maturity status comparison. Effects for 10-m sprinting and maximal aerobic speed were unclear.Integration of skeletal age and performance assessments indicated that conventional maturity status classification criteria were inconsistent to inform player development processes in our sample. Between-player differences in test performance may depend on a substantial delay in skeletal maturation (∆ ≤ -1.5 yr) and the performance outcome measure.

PURPOSE To provide the first scrutiny of adult height prediction protocols based on automated Greulich-Pyle and Tanner-Whitehouse (TW) skeletal ages applied to elite youth soccer players from the Middle East. METHODS We examined the application of modified Bayley-Pinneau (BoneXpert®), TW-II, and TW-III protocols using mixed-longitudinal data available for 103 subjects (chronological age range, 19.4 to 27.9 yr) previously enrolled as academy student-athletes (annual screening range, one to six visits). Random-effects generalized additive models quantified the presence of systematic mean differences between actual versus predicted adult height. Effects were deemed practically equivalent based on the location of the confidence interval (95% CI) against a realistic difference value of Δ = ± 1 cm. Each model pooled residual standard deviation described the actual precision of height predictions and was used to calculate a 95% prediction interval. RESULTS The BoneXpert® method overpredicted adult height systematically at chronological ages in the range of approximately 13.5 to 14.5 yr (95% CI range, -1.9 to -1 cm) and Greulich-Pyle skeletal ages between 13.5 and 15 yr (95% CI range, -3.1 to -1 cm). Effects based on TW-II were practically equivalent across the chronological and skeletal age measurement ranges, with this protocol yielding adult height predictions with a precision (standard deviation) of approximately ±2.6 cm. The mean TW-III effects indicated systematic adult height overpredictions until the attainment of 14.5 and 15 yr of chronological age (95% CI range, -3.8 to -1.1 cm) and TW-III skeletal age (95% CI range: -5.2 to -2.3 cm), respectively. CONCLUSIONS Tanner-Whitehouse-II adult height prediction method provided more consistent estimates and can be considered the method of choice for talent development purposes in youth soccer players from the Middle East.

Background and study objectives Adequate sleep is essential to support preparation and recovery processes for training and competition in athletes. A limited number of studies have examined whether adolescents from the Middle-East meet the minimum age-specific recommendations ranging from 8 to 9 h of night sleep based on objective measurements. This study aimed to provide an objective description of routine sleep habits in elite youth football players from the Middle-East. Methods Using wrist-worn actigraphy, we examined objective measures of sleep over a 14-day surveillance period from fifty-nine, male, Middle-Eastern elite youth football players (age range: 12.1 to 16 years). Results The observed median sleep duration was approximately 5.5 to 6 h during weekdays and 6.5 to 7.5 h over weekend days. Sleep intermissions resulting in two or more periods of sleep accounted for 8% and 17% of the data during weekdays and weekends, respectively. Conclusions For the first time, we reported an objective quantification of sleep measures indicating that elite youth athletes from the Middle-East do not meet the age-specific sleep recommendations. Integration of sleep tracking into the routine training monitoring process can be valuable to inform decisions relevant to the adoption of potential multidisciplinary interventions to address sleep insufficiency and disorders in youth athletes.

This investigation sought to determine whether post-exercise cold water immersion and low glycogen availability, separately and in combination, would preferentially activate either the Exon 1a or Exon 1b Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) promoter. Through a reanalysis of sample design, we identified that the systemic cold-induced augmentation of total PGC-1α gene expression observed previously (Allan et al. in J Appl Physiol 123(2):451–459, 2017) was largely a result of increased expression from the alternative promoter (Exon 1b), rather than canonical promoter (Exon 1a). Low glycogen availability in combination with local cooling of the muscle (Allan et al. in Physiol Rep 7(11):e14082, 2019) demonstrated that PGC-1α alternative promoter (Exon 1b) expression continued to rise at 3 h post-exercise in all conditions; whilst, expression from the canonical promoter (Exon 1a) decreased between the same time points (post-exercise–3 h post-exercise). Importantly, this increase in PGC-1α Exon 1b expression was reduced compared to the response of low glycogen or cold water immersion alone, suggesting that the combination of prior low glycogen and CWI post-exercise impaired the response in gene expression versus these conditions individually. Data herein emphasise the influence of post-exercise cooling and low glycogen availability on Exon-specific control of total PGC-1 α gene expression and highlight the need for future research to assess Exon-specific regulation of PGC-1α.

Talent identification (TID) and development (TDE) are large fields in professional soccer and in science. However, TID and TDE processes in youth academies have not been assessed in detail. As such, our aim was to survey professional clubs from around the world about their youth academy TID and TDE processes, with 29 clubs responding to the survey. TID and TDE processes changed as a function of player age. TID processes involved finding the best players locally and regionally, but for older players the search widened to nationally and internationally for the needs of the first team. Clubs used a multidisciplinary approach to TID, but more so with older players. Median number of academy players was 80, 100, and 66 players at 8-11 years, 12-16 years, and 17-21 years, respectively. Annual player turnover in the most recent season (selections/de-selections) was 29% across all age groups, with competition from other clubs cited as a limitation to TID. TDE processes involved weekly matches and 3-5 training sessions per week led by experienced, well-qualified coaches, with most clubs providing players with academic education, residency and transportation services. Our findings extend previous research assessing professional soccer youth academy TID and TDE processes by quantifying worldwide practices.

The purpose of this study was to present reference standards for physical performance test outcomes relevant to elite female soccer players. We analysed mixed-longitudinal data (n = 1715 observations) from a sample of 479 elite youth and senior players as part of the English Football Association's national development programme (age range: 12.7 to 36.0 years). Semi-parametric generalized additive models for location, scale and shape (GAMLSS) estimated age-related reference centiles for 5-m sprinting, 30-m sprinting, countermovement jump (CMJ) height, and Yo-Yo Intermittent Recovery Test Level 1 (Yo-Yo IR1) performance. The estimated reference centiles indicated that the median of the distribution of physical performance test scores varied non-linearly with advancing chronological age, improving until around 25 years for each performance variable. These are the first reference ranges for performance test outcomes in elite English female soccer players. These data can assist practitioners when interpreting physical test performance outcomes to track an individual's progress over time and support decision-making regarding player recruitment and development.

The youth-to-first team phase presents a number of challenges in the careers of modern football players with stagnation, inconsistent performance and dropout being reported. The aim of this study was to investigate the perception of staff involved in professional academy football clubs around the globe, with a particular focus on youth and first team transition demands, resources as well as transitions barriers and coping among male academy football players. Participants from 29 male youth academies distributed across 29 countries took part in the survey. Our main findings suggested training and match intensity reported as being greater at the senior-level and also pressure from parents. The majority of respondents indicated their clubs having long-term strategy for player development and specific roles supporting successful player transitions. Exposure to different playing styles was deemed important to prepare players for the first team. Likewise, having the academy and the first team training on the same site was perceived to ease the transition, with the majority of respondents indicating that players are able to cope with the pressure of first team training and games. Perceptions on whether staff do not have the skills/resources to prepare players for the changes in environment and culture when players move from youth-to-senior level were unclear. Collectively, our study extends previous transition research on youth football academies suggesting the importance of a club-based playing philosophy to prepare players for the first team demands and challenges.

This survey sought to establish current use, knowledge and perceptions of cold-water immersion (CWI) when used for recovery. 111 athletes, coaches and support practitioners completed the anonymous online survey, answering questions about their current CWI protocols, perceptions of benefits associated with CWI and knowledge of controlling mechanisms. Respondents were largely involved in elite sport at international, national and club level, with many having used CWI previously (86%) and finding its use beneficial for recovery (78%). Protocols differed, with the duration of immersion one aspect that failed to align with recommendations in the scientific literature. Whilst many respondents were aware of benefits associated with CWI, there remains some confusion. There also seems to be a gap in mechanistic knowledge, where respondents are aware of benefits associated with CWI, but failed to identify the underlying mechanisms. This identifies the need for an improved method of knowledge transfer between scientific and applied practice communities. Moreover, data herein emphasises the important role of the ‘support practitioner’ as respondents in this role tended to favour CWI protocols more aligned to recommendations within the literature. With a significant number of respondents claiming they were made aware of CWI for recovery through a colleague (43%), the importance of knowledge transfer and context being appropriately applied to data is as important as ever. With the firm belief that CWI is useful for recovery in sport, the focus should now be on investigating the psychophysiological interaction and correct use of this methodology.

Comment on: 1) Arthur J. Cheng. Cooling down the use of cryotherapy for post-exercise skeletal muscle recovery. Temperature. 2018. 5(2): 103-105. doi: 10.1080/23328940.2017.1413284. 2) Cheng et al. Post-exercise recovery of contractile function and endurance in humans and mice is accelerated by heating and slowed by cooling skeletal muscle. Journal of Physiology. 2017. 595(24): 7413-7426. doi: 10.1113/JP274870

OBJECTIVES: To support future developments of field-based biomechanical load monitoring tools, this study aimed to identify generalised segmental acceleration patterns and their contribution to ground reaction forces (GRFs) across different running tasks. DESIGN: Exploratory experimental design. METHODS: A multivariate principal component analysis (PCA) was applied to a combination of segmental acceleration data from all body segments for 15 team-sport athletes performing accelerated, decelerated and constant low-, moderate- and high-speed running, and 90° cutting trials. Segmental acceleration profiles were then reconstructed from each principal component (PC) and used to calculate their specific GRF contributions. RESULTS: The first PC explained 48.57% of the acceleration variability for all body segments and was primarily related to the between-task differences in the overall magnitude of the GRF impulse. Magnitude and timing of high-frequency acceleration and GRF features (i.e. impact related characteristics) were primarily explained by the second PC (12.43%) and also revealed important between-task differences. The most important GRF characteristics were explained by the first five PCs, while PCs beyond that primarily contained small contributions to the overall GRF impulse. CONCLUSIONS: These findings show that a multivariate PCA approach can reveal generalised acceleration patterns and specific segmental contributions to GRF features, but their relative importance for different running activities are task dependent. Using segmental acceleration to assess whole-body biomechanical loading generically across various movements may thus require task identification algorithms and/or advanced sensor or data fusion approaches. ispartof: JOURNAL OF SCIENCE AND MEDICINE IN SPORT vol:22 issue:12 pages:1355-1360 ispartof: location:Australia status: published

Talent identification and development programmes have received broad attention in the last decades, yet evidence regarding the predictive utility of physical performance in female soccer players is limited. Using a retrospective design, we appraised the predictive value of performance-related measures in a sample of 228 youth female soccer players previously involved in residential Elite Performance Camps (age range: 12.7 to 15.3 years). With 10-m sprinting, 30-m sprinting, counter-movement jump height, and Yo-Yo Intermittent Recovery Test Level 1 (IR1) distance as primary predictor variables, the Akaike Information Criterion (AIC) assessed the relative quality of four penalised logistic regression models for determining future competitive international squads U17-U20 level selection. The model including Yo-Yo IR1 was the best for predicting career outcome. Predicted probabilities of future selection to the international squad increased with higher Yo-Yo IR1 distances, from 4.5% (95% confidence interval, 0.8 to 8.2%) for a distance lower than 440 m to 64.7% (95% confidence interval, 47.3 to 82.1%) for a score of 2040 m. The present study highlights the predictive utility of high-intensity endurance capacity for informing career progression in elite youth female soccer and provides reference values for staff involved in the talent development of elite youth female soccer players.

Objective: To examine training and match loads undertaken by soccer players competing in the English Premier League.Methods: Using a retrospective design, external (GPS) and internal training loads...

Purpose: Using elite youth soccer players’ maximal sprinting speeds collected from a criterion and non-criterion measure, we demonstrate how expert practitioner opinion can be used to determine measurement validity. Methods: Expert soccer practitioners (n = 50) from around the world were surveyed on issues relating to the measurement of maximal sprinting speed and 12 elite youth soccer players performed two maximal 40 m sprints, measured by 10-Hz GPS units (non-criterion) and a 100-Hz Laser (criterion). Setting statistical equivalence bounds as practitioner opinion of the practically acceptable amount of measurement error for maximal sprinting speed, we assessed agreement between GPS and Laser. Results: Survey respondents reported a combination of methods for deriving maximal sprinting speed (tests, training, match) but most did not assess system validity. Median value of the practically acceptable amount of measurement error for maximal sprinting speed was 0.20 m/s. Maximal sprinting speed was 8.79 ± 0.33 m/s (Laser) and 8.75 ± 0.32 m/s (GPS), and the mean difference was 0.04 (90% confidence interval −0.03 to 0.11) m/s. Using the median acceptable amount of measurement error, we set our lower and upper equivalence bounds to −0.10 m/s and +0.10 m/s, respectively. Equivalence testing showed Laser and GPS as likely equivalent measures (probability 93.7%). Conclusion: Using expert-informed equivalence thresholds represents a novel way to assess validity in sports performance research. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group.

Introduction: Valid and informed interpretations of changes in physical performance test data are important within athletic development programmes. At present, there is a lack of consensus regarding a suitable method for deeming whether a change in physical performance is practically relevant or not.\ud \ud Methods: We compared true population variance in mean test scores between those derived from evidence synthesis of observational studies to those derived from practioner opinion (n = 30), and to those derived from a measurement error (minimal detectable change) quantification (n = 140). All these methods can help to obtain ‘target’ change score values for performance variables.\ud \ud Results: We found that the conventional ‘blanket’ target change of 0.2 (between-subjects SD) systematically underestimated practically relevant and more informed changes derived for 5-m sprinting, 30-m sprinting, CMJ, and Yo-Yo Intermittent Recovery Level 1 (IR1) tests in elite female soccer players.\ud \ud Conclusions: For the first time in the field of sport and exercise sciences, we have illustrated the use of a principled approach for comparing different methods for the definition of changes in physical performance test variables that are practically relevant. Our between-method comparison approach provides preliminary guidance for arriving at target change values that may be useful for research purposes and tracking of individual female soccer player’s physical performance.

ObjectivesTo describe age group patterns for injury incidence, severity and burden in elite male youth football.MethodsProspective cohort study capturing data on individual exposure and time-loss injuries from training and matches over four seasons (2016/2017 through 2019/2020) at a national football academy (U13–U18; age range: 11–18 years). Injury incidence was calculated as the number of injuries per 1000 hours, injury severity as the median number of days lost and injury burden as the number of days lost per 1000 hours.ResultsWe included 301 players (591 player-seasons) and recorded 1111 time-loss injuries. Overall incidence was 12.0 per 1000 hours (95% CI 11.3 to 12.7) and burden was 255 days lost per 1000 hours (252 to 259). The mean incidence for overall injuries was higher in the older age groups (7.8 to 18.6 injuries per 1000 hours), while the greatest burden was observed in the U16 age group (425 days; 415 to 435). In older age groups, incidence and burden were higher for muscle injuries and lower for physis injuries. Incidence of joint sprains and bone stress injuries was greatest for players in the U16, U17 and U18 age groups, with the largest burden observed for U16 players. No clear age group trend was observed for fractures.ConclusionInjury patterns differed with age; tailoring prevention programmes may be possible.

The current study examined how sleep may be influenced by the scheduling of training and match load within 10 youth-soccer players. Sleep was measured over a 14-day in-season period using a commercially available wireless sleep monitor. Each collected sleep variable; lights out, sleep latency, total sleep time wake after sleep onset and final awakening, was compared for the specific day within the training schedule (e.g. match day [MD], day after match [MD + 1]) and to training/match load (high-speed distance (>5.5 m/s) [HSD] and rating of perceived exertion. The data were analysed using mixed models and effect sizes, to describe the magnitude of effects that training schedule and training load may have on sleep. A reduction of sleep duration was observed on the day after the match (MD + 1) in relation to the training days preceding the match (MD-2: −65 min, ES: 0.89 ± 0.79; MD-1 −61 min, ES: 0.82 ± 0.64) and reduction on match day (+45 min; ES: 1.91 ± 1.69). This may suggest youth-soccer players actively change their sleep scheduling behaviours in relation to the imposed soccer schedule. Increased high-speed running (for every 100 m) showed a small increase to total sleep time (+9 min; ES: 0.48 ± 0.31). This may suggest that increases in training load may be associated with small increases in sleep quantity. Such observations may highlight that the type of day and the associated load within the training microcycle may have important consequences for sleep within youth-soccer players.

Mechanisms mediating postexercise cold-induced increases in PGC-1α gene expression in human skeletal muscle are yet to be fully elucidated but may involve local cooling effects on AMPK and p38 MAPK-related signaling and/or increased systemic β-adrenergic stimulation. Therefore, we aimed to examine whether postexercise cold water immersion enhancement of PGC-1α mRNA is mediated through local or systemic mechanisms. Ten subjects completed acute cycling (8 × 5 min at ~80% peak power output) followed by seated-rest (CON) or single-leg cold water immersion (CWI; 10 min, 8°C). Muscle biopsies were obtained preexercise, postexercise, and 3 h postexercise from a single limb in the CON condition but from both limbs in CWI [thereby providing tissue from a CWI and nonimmersed limb (NOT)]. Muscle temperature decreased up to 2 h postexercise following CWI (−5°C) in the immersed limb, with lesser changes observed in CON and NOT (−3°C, P < 0.05). No differences between limbs were observed in p38 MAPK phosphorylation at any time point ( P < 0.05), whereas a significant interaction effect was present for AMPK phosphorylation ( P = 0.031). Exercise (CON) increased gene expression of PGC-1α 3 h postexercise (~5-fold, P < 0.001). CWI augmented PGC-1α expression above CON in both the immersed (CWI; ~9-fold, P = 0.003) and NOT limbs (~12-fold, P = 0.001). Plasma normetanephrine concentration was higher in CWI vs. CON immediately postimmersion (860 vs. 665 pmol/l, P = 0.034). We report for the first time that local cooling of the immersed limb evokes transcriptional control of PGC-1α in the nonimmersed limb, suggesting increased systemic β-adrenergic activation of AMPK may mediate, in part, postexercise cold induction of PGC-1α mRNA. NEW & NOTEWORTHY We report for the first time that postexercise cold water immersion of one limb also enhances PGC-1α expression in a contralateral, nonimmersed limb. We suggest that increased systemic β-adrenergic stimulation, and not localized cooling per se, exerts regulatory effects on local signaling cascades, thereby modulating PGC-1α expression. Therefore, these data have important implications for research designs that adopt contralateral, nonimmersed limbs as a control condition while also increasing our understanding of the potential mechanisms underpinning cold-mediated PGC-1α responses.

During the competitive season, soccer players are likely exposed to numerous factors that may disrupt the process of sleep. The current investigation looked to evaluate a practical sleep hygiene strategy (10-min showering at ∼40°C before lights out), within a group of 11 youth soccer players in comparison to normal sleeping conditions (control). Each condition consisted of three days within a randomised crossover trial design. Sleep information was collected using a commercial wireless bedside sleep monitor. Measures of skin temperature were evaluated using iButton skin thermistors to establish both distal and proximal skin temperatures and distal to proximal gradient. The shower intervention elevated distal skin temperature by 1.1°C (95% CI: 0.1-2.1°C, p = .04) on average prior to lights out. The elevation in distal temperature was also present during the first 30-min following lights out (1.0°C, 95% CI: 0.4-1.6°C, p

Purpose: Cold-water immersion (CWI) and whole body cryotherapy (WBC) are widely used recovery methods in an attempt to limit exercise-induced muscle damage, soreness and functional deficits after strenuous exercise. The aim of this study was to compare the effects of ecologically-valid CWI and WBC protocols on post-exercise lower limb thermoregulatory, femoral artery and cutaneous blood flow responses.Methods: Ten males completed a continuous cycle exercise protocol at 70% maximal oxygen uptake until a rectal temperature of 38°C was attained. Participants were then exposed to lower-body CWI (8°C) for 10 min, or WBC (-110°C) for 2 min, in a randomized cross-over design. Rectal and thigh skin, deep and superficial muscle temperatures, thigh and calf skin blood flow (laser Doppler flowmetry), superficial femoral artery blood flow (duplex ultrasound) and arterial blood pressure were measured prior to, and for 40 min post, cooling interventions.Results: Greater reductions in thigh skin (CWI, -5.9±1.8°C; WBC, 0.2±0.5°C; P < 0.001) and superficial (CWI, -4.4±1.3°C; WBC, -1.8±1.1°C; P < 0.001) and deep (CWI, -2.9±0.8°C; WBC, -1.3±0.6°C; P < 0.001) muscle temperatures occurred immediately after CWI. Decreases in femoral artery conductance were greater after CWI (CWI, -84±11%; WBC, -59±21%, P < 0.02) and thigh (CWI, -80±5%; WBC, -59±14%, P < 0.001) and calf (CWI, -73±13%; WBC, -45±17%, P < 0.001) cutaneous vasoconstriction was greater following CWI. Reductions in rectal temperature were similar between conditions after cooling (CWI, -0.6±0.4°C; WBC, -0.6±0.3°C; P = 0.98).Conclusion: Greater reductions in blood flow and tissue temperature were observed after CWI in comparison to WBC. These novel findings have practical and clinical implications for the use of cooling in the recovery from exercise and injury.

© 2017 Human Kinetics, Inc. Monitoring the load placed on athletes in both training and competition has become a very hot topic in sport science. Both scientists and coaches routinely monitor training loads using multidisciplinary approaches, and the pursuit of the best methodologies to capture and interpret data has produced an exponential increase in empirical and applied research. Indeed, the field has developed with such speed in recent years that it has given rise to industries aimed at developing new and novel paradigms to allow us to precisely quantify the internal and external loads placed on athletes and to help protect them from injury and ill health. In February 2016, a conference on "Monitoring Athlete Training Loads-The Hows and the Whys" was convened in Doha, Qatar, which brought together experts from around the world to share their applied research and contemporary practices in this rapidly growing field and also to investigate where it may branch to in the future. This consensus statement brings together the key findings and recommendations from this conference in a shared conceptual framework for use by coaches, sport-science and-medicine staff, and other related professionals who have an interest in monitoring athlete training loads and serves to provide an outline on what athlete-load monitoring is and how it is being applied in research and practice, why load monitoring is important and what the underlying rationale and prospective goals of monitoring are, and where athlete-load monitoring is heading in the future.

Kyprianou, E, Di Salvo, V, Lolli, L, Al Haddad, H, Villanueva, AM, Gregson, W, and Weston, M. To measure peak velocity in soccer, let the players sprint. J Strength Cond Res 36(1): 273-276, 2022-Expressing externals loads relative to a player's individual capacities has potential to enhance understanding of dose-response. Peak velocity is an important metric for the individualization process and is usually measured during a sprint test. Recently, however, peak velocity was reported to be faster during soccer matches when compared with a 40-m sprint test. With the aim of developing the practice of individualized training prescription and match evaluation, we examined whether the aforementioned finding replicates in a group of elite youth soccer players across a broader range of soccer activities. To do this, we compared the peak velocities of 12 full-time male youth soccer players (age 16.3 ± 0.8 years) recorded during a 40-m sprint test with peak velocity recorded during their routine activities (matches, sprints, and skill-based conditioning drills: small-sided games [SSG], medium-sided games [MSG], large-sided games [LSG]). All activities were monitored with 10-Hz global positioning systems (Catapult Optimeye S5, version 7.32) with the highest speed attained during each activity retained as the instantaneous peak velocity. Interpretation of clear between-activity differences in peak velocity was based on nonoverlap of the 95% confidence intervals for the mean difference between activities with sprint testing. Peak velocity was clearly faster for the sprint test (8.76 ± 0.39 m·s-1) when compared with matches (7.94 ± 0.49 m·s-1), LSG (6.94 ± 0.65 m·s-1), MSG (6.40 ± 0.75 m·s-1), and SSG (5.25 ± 0.92 m·s-1), but not sprints (8.50 ± 0.36 m·s-1). Our data show the necessity for 40-m sprint testing to determine peak velocity.

We aimed to assess the coach-player agreement of subjective soccer training loads via differential ratings of perceived exertion (dRPE). The coach initially underwent quantifiable familiarisation (blackness test) with the Borg CR100 scale. Data were collected from 16 semi-professional soccer players across seven consecutive training sessions. For the measurement of subjective training load, the coach and players provided dRPE (CR100) for legs (RPE-L), breathlessness (RPE-B) and technical exertion (RPE-T). Coach-prescribed dRPE were recorded prior to training, with coach observed and player reported dRPE collected post training. Statistical equivalence bounds for agreement between coach (prescribed and observed) and player reported dRPE scores were 4 arbitrary units on the CR100 and we used a probability outcome of likely (≥75%) to infer realistic equivalence. Following three familiarisation sessions, the coach improved their blackness test score from 39% to 83%. Coach observed and player reported RPE-T scores were likely equivalent, with all other comparisons not realistically equivalent. Since training prescription is coach-led, our data highlight the importance of accurate internal load measurement and feedback in soccer. The improved accuracy and precision of coach intensity estimation after three attempts at the blackness test suggests that this method could be worthwhile to researchers and practitioners employing dRPE.

Training and competition loads have emerged as modifiable composite risk factors of non‐contact injury. Hamstring strains are the most common injuries in football with substantial burden on the individual player and club. Nevertheless, robust evidence of a consistent load‐hamstring injury relationship in professional football is lacking. Using available data from the Qatar Stars League over three competitive seasons, this study investigated the separate and combined effects of perceived exertion and session duration on hamstring injury occurrence in a sample of 30 outfield football players. Load variables were calculated into 7‐day, 14‐day, 21‐day, 28‐day periods of data, and week‐to‐week changes for average ratings of perceived exertion (RPE; au) score and session‐RPE (s‐RPE; session‐duration urn:x-wiley:09057188:media:sms13591:sms13591-math-0001 score), plus the cumulative training and match minutes and s‐RPE, respectively. Conditional logistic regression models estimated load‐injury relationships per 2‐within‐subject standard deviation increments in each candidate variable. Associations were declared practically important based on the location of the confidence interval in relation to thresholds of 0.90 and 1.11 defining small beneficial and harmful effects, respectively. The uncertainty for the corrected odds ratios show that typically high within‐subject increments in each candidate variable were not practically important for training‐ and match‐related hamstring injury (95% confidence intervals range: 0.85 to 1.16). We found limited exploratory evidence regarding the value of perceived exertion and session duration as etiological factors of hamstring injury in Middle‐East professional football. Monitoring remains valuable to inform player load management strategies, but our exploratory findings suggest its role for type‐specific injury risk determination appears empirically unsupported.

We assessed the effects of post‐exercise cold‐water immersion (CWI) in modulating PGC‐1α mRNA expression in response to exercise commenced with low muscle glycogen availability. In a randomized repeated‐measures design, nine recreationally active males completed an acute two‐legged high‐intensity cycling protocol (8 × 5 min at 82.5% peak power output) followed by 10 min of two‐legged post‐exercise CWI (8°C) or control conditions (CON). During each trial, one limb commenced exercise with low (LOW

Running impact forces expose the body to biomechanical loads leading to beneficial adaptations, but also risk of injury. High-intensity running tasks, especially, are deemed highly demanding for the musculoskeletal system, but loads experienced during these actions are not well understood. To eventually predict GRF and understand the biomechanical loads experienced during such activities in greater detail, this study aimed to (1) examine the feasibility of using a simple two mass-spring-damper model, based on eight model parameters, to reproduce ground reaction forces (GRFs) for high-intensity running tasks and (2) verify whether the required model parameters were physically meaningful. This model was used to reproduce GRFs for rapid accelerations and decelerations, constant speed running and maximal sprints. GRF profiles and impulses could be reproduced with low to very low errors across tasks, but subtler loading characteristics (impact peaks, loading rate) were modelled less accurately. Moreover, required model parameters varied strongly between trials and had minimal physical meaning. These results show that although a two mass-spring-damper model can be used to reproduce overall GRFs for high-intensity running tasks, the application of this simple model for predicting GRFs in the field and/or understanding the biomechanical demands of training in greater detail is likely limited. ispartof: SPORTS BIOMECHANICS vol:20 issue:5 ispartof: location:England status: published

The aim of the present investigation was to determine the relationship between blood creatine kinase (CK) and physical match performance in elite male soccer players. Fifteen elite outfield soccer players (mean ± S.D.; age, 26 ± 4 years; height, 1.8 ± 0.6 m; body mass, 84 ± 6 kg) who played for a professional soccer team competing in the English Premier League were examined. Blood samples were collected 48 hrs following a competitive match. Analysis for CK concentration was performed immediately after collection via spectrophotometry using a commercially available reagent kit (Reflotron® Systems, Roche, Mannheim, Germany). Physical match performance data was collected using a computerised tracking system (Prozone®) from > 6 matches for each player. The physical performance variables selected to examine the relationship between CK and physical match performance included total distance, total high-intensity running distance, total high-intensity running number of efforts, total sprint distance, total sprint number of efforts, average speed and recovery time. Mean ± S.D CK concentration 48 hrs post match was 520 ± 224 µ.mol.l-1 though large individual variation in the CK response at this time point was observed (184 µ.mol.l-1 to 1573 µ.mol.l-1). No significant correlation coefficients were obtained between any of the chosen indicators of physical match performance and CK concentration 48 hrs post match. This data would suggest that CK concentrations are elevated as a consequence of playing a soccer match. Creatine kinase may be of limited value in tracking subtle changes in the performance of players during the competitive season.

This study investigated the positional differences in physical performance of elite youth footballers in a tournament scenario and the influence of team success and opponent quality on team physical and technical performance. Match performance observations were collected using a semi-automated multi-camera tracking system across 2 elite under-17 international club tournaments from all players and teams (n = 1,457 individual cases). Teams were classified based on their final tournament ranking as top (1–4 ranking), middle (5–8 ranking) and bottom (9–12 ranking). Technical performance measures were expressed in absolute terms and relative to the time the team was in ball possession. Positional differences in physical performance and the influence of team success and opponent quality on team match performance were identified using a generalised linear mixed model. Positional differences were similar to that observed in elite senior players. Top ranking teams performed a greater number of absolute and...

Purpose:To quantify the mean daily changes in training and match load and any parallel changes in indicators of morningmeasured fatigue across in-season training weeks in elite soccer players.Methods:After each training session and match (TL), session ratings of perceived exertion (s-RPE) were recorded to calculate overall session load (RPE-TL) in 29 English Premier League players from the same team. Morning ratings of fatigue, sleep quality, and delayed-onset muscle soreness (DOMS), as well as submaximal exercise heart rate (HRex), postexercise heart-rate recovery (HRR%), and heart-rate variability (HRV) were recorded before match day and 1, 2, and 4 d postmatch. Data were collected for a median duration of 3 wk (range 1–13) and reduced to a typical weekly cycle including no midweek match and a weekend match day. Data were analyzed using withinsubject linear mixed models.Results:RPE-TL was approximately 600 arbitrary units (AU) (95% confidence interval 546–644) higher on match day than following day (P < .001). RPE-TL progressively decreased by »60 AU per day over the 3 days before a match (P < .05). Morning-measured fatigue, sleep quality, and DOMS tracked the changes in RPE-TL, being 35–40% worse on postmatch day vs prematch day (P < .001). Perceived fatigue, sleep quality, and DOMS improved by 17–26% from postmatch day to 3 d postmatch, with further smaller (7%–14%) improvements occurring between 4 d postmatch and prematch day (P < .01). There were no substantial or statistically significant changes in HRex, HRR%, or HRV over the weekly cycle (P > .05).Conclusions:Morning-measured ratings of fatigue, sleep quality, and DOMS are clearly more sensitive than HR-derived indices to the daily fluctuations in session load experienced by elite soccer players in a standard in-season week.

The measurement of relative physiological stress during training is important because this is the stimulus for the long-term adaptive response. Measurements of perceived exertion (RPE) have been reported to correlate with the heart rate during field-based training sessions. Nevertheless, there are few studies on how well RPE tracks with the heart rate over repeated training sessions in elite soccer players. Therefore, we aimed to quantify the within-participant correlations between variability in session-RPE (sRPE) and the heart rate in elite male soccer players, and to determine whether the playing position moderated these correlations. The field-based training of four central defenders, four wide defenders, six central midfielders, two wide midfielders and three attackers from an elite English Premier League squad were monitored over an entire in-season competitive period, giving a total of 1010 individual training sessions for study. Correlations between session-RPE and heart rates were quantified using a within-participant model. The correlation between changes in sRPE and heart rates was r = 0.75 (95% CI: 0.71-0.78). This correlation remained high across the various player positions (wide-defender, r = 0.81; central-defender, r = 0.74; wide midfielder, r = 0.70; central midfielder, r = 0.70; attacker, r = 0.84; P

Objectives To investigate the impact of physical efforts performed in the period preceding activity as a potential risk factor of muscle injury during match-play within a sample of professional soccer players. Design Observational cohort study. Methods Match load (running [>14.4–19.8 km/h], high-speed running [>19.8–25.2 km/h], sprinting [>25.2 km/h], leading and explosive sprint type) averaged in 1-min and 5-min periods prior to an event or non event for 29 professional outfield soccer players. Conditional logistic and Poisson regression models estimated the relationship between load and injury for a 2 within-subject standard deviation in match load or 1-action increment in the number of sprinting activities, respectively. Associations were deemed beneficial or harmful based on non-overlap of the 95% confidence intervals against thresholds of 0.90 and 1.11, respectively. Results An increment in sprinting distance [+2-SDs = 11 m] covered over a 1-min period (odds ratio [OR]: 1.22, 95%CI, 1.12 to 1.33) increased the odds of muscle injury. Conclusions Our study provides novel exploratory evidence that the volume of sprinting during competitive soccer match-play has a harmful association with muscle injury occurrence.

Objectives: The study examined if three feasible strategies involving additional in-play cooling periods attenuate the core (rectal) temperature rise during simulated football matches. Design: Four counterbalanced experimental trials in an environmental chamber set to 35 °C ambient temperature, 55% relative humidity, and 30 °C WBGT. Methods: Twelve healthy well-trained football players completed a regular simulated match (REG), regular simulated match with additional 3-min cooling periods at the 30-min mark of each half inclusive of chilled water consumption (COOLwater), regular simulated match with additional 3-min cooling periods at the 30-min mark of each half inclusive of chilled water consumption and the application of an ice towel around the neck (COOLtowel), regular simulated match with an extended (+5 min; total of 20-min) half-time break (HTextended). Results: The difference in rectal temperature change was significantly lower in the COOLwater (−0.25 °C), COOLtowel (−0.28 °C), and HTextended (−0.21 °C) trials in comparison to the REG (all p < 0.05). Exercising heart rate and session rating of perceived exertion was lower in the COOLwater (−13 bpm; −1.4 au), COOLtowel (−10 bpm; −1.3 au), and HTextended (−8 bpm; −0.9 au) trials in comparison to the REG trial (all p < 0.05). The cooling interventions did not significantly change skin temperature or thermal sensation in comparison to the REG (all p > 0.05). Conclusions: All three cooling interventions attenuated core body thermal strain during simulated matches. The laboratory-based study supports the use of brief in-play cooling periods as a means to attenuate the rise in core temperature during matches in hot and humid conditions Refereed/Peer-reviewed

Objective Skeletal muscle is unique among organs in that its blood flow, thus oxygen supply that is critical for muscular function, can change over a remarkably large range. Compared to the rest, muscle blood flow can increase over 20-fold during intense exercise. Positron emission tomography (PET) and [15O]-H2O tracer provide a unique tool for the direct measurement of muscle blood flow in specific muscle regions. Quantification of PET blood flow requires knowledge of the arterial input function, which is usually provided by arterial blood sampling. However, arterial sampling is an invasive approach requiring arterial cannulation. In the current study, we aimed to explore the analysis and error estimation based on non-invasive, PET image-based input function for skeletal muscle blood flow in PET [15O]-labeled radiowater study. Methods Thirty healthy untrained men volunteered to participate in this study. [15O]-labeled radio water PET perfusion scans were performed at rest and right after cycling exercise. GE Discovery PET-CT scanner was used for image acquisition. The 15O isotope was produced with a Cyclone 3 cyclotron (IBA Molecular, Belgium). After 455 MBq of 15O-H2O was injected intravenously and after 20 seconds, dynamic scanning images were performed in following frames: 6x5 seconds, 12x10 seconds, 7x30 seconds and 12x10 seconds. Arterial blood was sampled continuously from radial artery during imaging for radioactivity with a detector during PET scanning. All the data analysis was performed using all in-house developed programs. Arterial input function was preprocessed with delay correction. Image-based input function was defined based on sum image of dynamic images. Blood flow was calculated using the 1-tissue compartment model, k1 is considered as blood flow without any further correction. All data analysis was performed by Carimas software (http://www.turkupetcentre.fi/carimas). Data analysis was performed in five parts: 1) Modelling data using input function from artery. 2) By defining femoral artery Volume Of Interest (VOI) on PET images. 3) Modelling data using image-based input function. 4) Calculating the correlation for blood flow between artery (blood) input function and image-based input function. 5) Predicted true blood flow was calculated based on correlation based on the initial linear relationship between blood and image-based input functions. Results Skeletal muscle blood flow had a good linear relationship calculated by femoral artery VOI and by arterial (blood) input function (y = 2,9587x - 0,096, R² = 0,8852, p

The purpose of the present study was to provide a detailed analysis of the repeated high-speed demands of competitive international female soccer match-play. A total of 148 individual match observations were undertaken on 107 outfield players in competitive international matches during the 2011-2012 and 2012-2013 seasons, using a computerized tracking system (STATS, Leeds, England). High-speed activity was classified as either sprint activity (SA) or high-speed running (HSR), with thresholds of >25.1 km.h-1 or >19.8 km.h-1 applied respectively. Repeated sprint activity (RSA) was defined as a minimum of two sprints with 20 s or less recovery between sprints and repeated high-speed activity (RHSA) was defined as a minimum of two high-speed runs or sprints with 20 s or less recovery between efforts. HSR bouts occurred ~5 times more frequently than SA bouts. Central defenders completed 50-80 fewer HSR bouts (moderate count ratio (CR): range 0.61-0.70) and 10-20 fewer SA bouts (moderate CR: range 0.53-0.69) than all other playing positions. RSA bouts occurred less frequently than RHSA bouts (33 ± 10 v 1.1 ± 1.1) with 37 % of players failing to complete any RSA bouts. Central defenders completed fewer RHSA bouts compared to all other playing positions (moderate CR: range 0.57-0.69). Consideration of both RHSA and RSA bouts is necessary to ensure a comprehensive understanding of the demands of female match-play. Practitioners can utilise this information to construct position-specific training and testing programmes which are aligned to the RHSA demands of match-play for elite female players.

OBJECTIVES: Unlike physiological loads, the biomechanical loads of training in running-based sports are still largely unexplored. This study, therefore, aimed to assess the validity of estimating ground reaction forces (GRF), as a measure of external whole-body biomechanical loading, from segmental accelerations. METHODS: Fifteen team-sport athletes performed accelerations, decelerations, 90° cuts and straight running at different speeds including sprinting. Full-body kinematics and GRF were recorded with a three-dimensional motion capture system and a single force platform respectively. GRF profiles were estimated as the sum of the product of all fifteen segmental masses and accelerations, or a reduced number of segments. RESULTS: Errors for GRF profiles estimated from fifteen segmental accelerations were low (1-2Nkg-1) for low-speed running, moderate (2-3Nkg-1) for accelerations, 90° cuts and moderate-speed running, but very high (>4Nkg-1) for decelerations and high-speed running. Similarly, impulse (2.3-11.1%), impact peak (9.2-28.5%) and loading rate (20.1-42.8%) errors varied across tasks. Moreover, mean errors increased from 3.26±1.72Nkg-1 to 6.76±3.62Nkg-1 across tasks when the number of segments was reduced. CONCLUSIONS: Accuracy of estimated GRF profiles and loading characteristics was dependent on task, and errors substantially increased when the number of segments was reduced. Using a direct mechanical approach to estimate GRF from segmental accelerations is thus unlikely to be a valid method to assess whole-body biomechanical loading across different dynamic and high-intensity activities. Researchers and practitioners should, therefore, be very cautious when interpreting accelerations from one or several segments, as these are unlikely to accurately represent external whole-body biomechanical loads. ispartof: JOURNAL OF SCIENCE AND MEDICINE IN SPORT vol:22 issue:6 pages:716-722 ispartof: location:Australia status: published

An important question for researchers and practitioners is whether an individual’s risk of injury increases if they make prior changes to their training load.1 In this field of research, ‘load’ typically refers to in-training distances covered, speed and accelerations.1 Attention has generally focused on whether a person’s acute (eg, 7 day) increase in load, normalised to that person’s prior ‘baseline’ of chronic (eg, 28 day) load, predicts injury.1 To obtain this normalised predictor, acute load is typically divided by chronic load to provide the acute-to-chronic workload ratio (ACWR).1 Fundamentally, simple ratios (Y/X) are formulated to ‘ control for ’ a denominator variable (eg, preceding chronic load) that is perceived to have an important biological influence on the numerator variable (eg, acute load).2 Within this notion of ‘ control for ’,3 it is generally posited that the denominator is a ‘nuisance’ variable that is associated with the numerator of interest.2 Logically, a simple ratio index provides meaningful relative measures for clinical and prognostic purposes only if (1) there is a ‘true’ and ‘proportional’ association between numerator and denominator in the first place, and (2) the ratio normalises for the denominator in a consistent manner for all individuals in the measurement range.2 We have demonstrated recently that the typical practice in the current literature1 of including, …

Purpose:To quantify the relationship between daily training load and a range of potential measures of fatigue in elite soccer players during an in-season competitive phase (17 d).Methods:Total high-intensity-running (THIR) distance, perceived ratings of wellness (fatigue, muscle soreness, sleep quality), countermovement-jump height (CMJ), postexercise heart-rate recovery (HRR), and heart-rate variability (Ln rMSSD) were analyzed during an in-season competitive period (17 d). General linear models were used to evaluate the influence of daily fluctuation in THIR distance on potential fatigue variables.Results:Fluctuations in fatigue (r = −.51, large, P < .001), Ln rMSSD (r = −.24, small, P = .04), and CMJ (r = .23, small, P = .04) were significantly correlated with fluctuations in THIR distance. Correlations between variability in muscle soreness, sleep quality, and HRR and THIR distance were negligible and not statistically significant.Conclusions:Perceived ratings of fatigue and Ln rMSSD were sensitive to daily fluctuations in THIR distance in a sample of elite soccer players. Therefore, these particular markers show promise as simple, noninvasive assessments of fatigue status in elite soccer players during a short in-season competitive phase.

Purpose: The aim of the current study was to identify the external-training-load markers that are most influential on session rating of perceived exertion (RPE) of training load (RPE-TL) during elite soccer training. Methods: Twenty-two elite players competing in the English Premier League were monitored. Training-load data (RPE and 10-Hz GPS integrated with a 100-Hz accelerometer) were collected during 1892 individual training sessions over an entire in-season competitive period. Expert knowledge and a collinearity r < .5 were used initially to select the external training variables for the final analysis. A multivariateadjusted within-subjects model was employed to quantify the correlations of RPE and RPE-TL (RPE × duration) with various measures of external training intensity and training load. Results: Total high-speed-running (HSR; >14.4 km/h) distance and number of impacts and accelerations >3 m/s2 remained in the final multivariate model (P < .001). The adjusted correlations with RPE were r = .14, r = .09, and r = .25 for HSR, impacts, and accelerations, respectively. For RPE-TL, the correlations were r = .11, r = .45, and r = .37, respectively. Conclusions: The external-load measures that were found to be moderately predictive of RPE-TL in soccer training were HSR distance and the number of impacts and accelerations. These findings provide new evidence to support the use of RPE-TL as a global measure of training load in elite soccer. Furthermore, understanding the influence of characteristics affecting RPE-TL may help coaches and practitioners enhance training prescription and athlete monitoring.

Match congestion in elite soccer has been proposed to result in residual fatigue and underperformance in ensuing competition due to insufficient recovery time. In this article, matters relating to match congestion and running performance in elite soccer competition are discussed. The authors suggest a need to determine the extent to which elite players are in reality exposed to periods of match congestion hence to potential declines in performance. Despite evidence of exercise-induced muscle damage combined with a decline in physical performance up to 72-hours post-match, research using time-motion analyses suggest running performance represented by distances covered is unaffected over periods of match congestion. The authors recommend analysis of alternative movement variables including accelerations, decelerations and turns that are taxing metabolically and contribute greatly to muscle damage. Moreover, a holistic approach combining subjective ratings with biochemical, hormonal and immunological responses to exercise would be pertinent especially in players frequently exposed to match congestion. Contemporary practitioners typically implement various post-match recovery treatments during dense schedules in an attempt to accelerate recovery and ensure that subsequent running performance is not unduly affected. However, empirical evidence to support their efficacy in maintaining running performance is lacking and the authors recommend controlled intervention studies using match simulations in an attempt to verify their effectiveness. These points are critically addressed using findings from the current scientific literature while gaps in the current body of knowledge and future directions for research are highlighted.