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BACKGROUND: Tennis is one of the most popular sports among youths. At elite levels, a notable increase in injury incidence and a temporary decline in performance may occur when children progress through puberty. However, limited research has explored maturity-associated variations in clinical measurements suggested as predictors of injury and tennis performance in elite youth players. Therefore, the main purpose of this study was to analyze the association between chronological age and maturity status on several measures of neuromuscular capability and physical performance as well as bilateral (interlimb) asymmetries in elite youth tennis players. HYPOTHESIS: Youth tennis players around peak height velocity (PHV) will show higher growth-related impairments or deficits in measures of neuromuscular capability and physical performance than their less (pre-PHV) and more (post-PHV) mature counterparts irrespective of sex. LEVEL OF EVIDENCE: Level 4. METHODS: A total of 68 male (age, 13.7 ± 1.1 years; height, 162.4 ± 9.4 cm; body mass, 51.4 ± 10.3 kg [Mean values ± SD]) and 60 female (age, 13.6 ± 1.1 years; height, 162.8 ± 7.2 cm; body mass, 52.7 ± 7.5 kg [Mean values ± SD]) elite youth tennis players from 2 different age groups (under 13 [U13] and under 15 [U15]) and maturity status (pre-PHV, around PHV, and post-PHV), were tested during national training camps. Tests included the Y Balance Test, isometric hip abduction and adduction strength, hip ranges of motion (ROMs), and countermovement jump (CMJ) height. Bayesian analysis was used to establish any significant between-group differences. RESULTS: Only dynamic balance (in boys; Bayesian factor [BF10] = 88.2) and jump height (in both boys and girls; BF10 >100) were significatively associated with chronological age, whereby the U15 group showed lower Y Balance Test reach distances (-6%; standardized effect size δ = 0.62) but higher CMJ height scores (+18%; δ = 0.73) than the U13 group. Although boys jump higher (+11%; δ = 0.62) and were stronger in isometric hip adduction strength (+14%; δ = 0.92) than girls, the latter had greater hip internal ROM values (+15%; δ = 0.75). Furthermore, relevant maturity-associated effects (BF10 = 34.6) were solely observed for the CMJ test in boys, with the most mature players demonstrating higher jump height scores (+12%; δ = 0.93). Finally, a significant percentage (>25%) of tennis players, independent of sex, demonstrated bilateral asymmetries in hip ROM, hip strength, and jump height values. CONCLUSION: The findings of this study show that in U13 and U15 male and female tennis players, there were neither positive nor negative maturity-associated variations in the clinical measurements analyzed (with the exception of jump height in male players). The high proportion of tennis players showing bilateral asymmetries in dynamic balance, hip ROM, and strength and jump performance highlight the need of future studies to analyze these factors in relation to unilateral tennis-specific adaptations in the musculoskeletal and sensorimotor systems. CLINICAL RELEVANCE: These results may help to better understand how different clinical measurements are associated with the process of growth and maturation in elite youth tennis players and may aid in the design of specific training interventions during these stages of development.

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ABSTRACT: Clarke, R, Read, PJ, De Ste Croix, MBA, and Hughes, JD. The deceleration deficit: a novel field-based method to quantify deceleration during change of direction performance. J Strength Cond Res 36(9): 2434-2439, 2022-The study investigated the relationship between linear and change of direction (COD) speed performance components and the individual differences between deceleration deficit (DD) and COD deficit (CODD). Thirty-six subjects (mean ± SD : age = 20.3 ± 2.9 years; stature = 175.2 ± 7.7 cm; and body mass = 78.0 ± 16.7 kg) completed 3 trials of a 505 test in both turning directions (dominant [D]; nondominant [ND]) and 3 15-m linear sprints. Deceleration deficit was calculated by the 15-m approach in the 505 test, minus the athlete's linear 15-m sprint time. To compare individuals CODD and DD, z-scores were calculated, and moderate worthwhile changes (MWCs) were identified between these deficit z-scores. Significant correlations were identified between linear sprints and 505 time (D: r = 0.71, 0.74; P < 0.01. ND: r = 0.76, 0.75; P < 0.01) for 10-m and 15-m sprint. respectively, and between 505 performance and CODD (D: r = 0.74; P < 0.01. ND: r = 0.77; P < 0.01) and DD (D: r = 0.41, P < 0.05. ND: r = 0.44, P < 0.01). Deceleration deficit was significantly related to CODD (D: r = 0.59; P < 0.01. ND: r = 0.62; P < 0.01); however, 78% of subjects demonstrated differences between these deficit measures greater than an MWC. In conclusion, linear speed has the strongest significant relationship with 505 performance. Deceleration deficit could provide a more isolated construct than CODD which may be related to an athlete's deceleration capabilities.

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Female soccer has seen a substantial rise in participation, as well as increased financial support from governing bodies over the last decade. Thus, there is an onus on researchers and medical departments to develop a better understanding of the physical characteristics and demands, and the health and performance needs of female soccer players. In this review, we discuss the current research, as well as the knowledge gaps, of six major topics: physical demands, talent identification, body composition, injury risk and prevention, health and nutrition. Data on female talent identification are scarce, and future studies need to elucidate the influence of relative age and maturation selection across age groups. Regarding the physical demands, more research is needed on the pattern of high-intensity sprinting during matches and the contribution of soccer-specific movements. Injuries are not uncommon in female soccer players, but targeting intrinsically modifiable factors with injury prevention programmes can reduce injury rates. The anthropometric and physical characteristics of female players are heterogeneous and setting specific targets should be discouraged in youth and sub-elite players. Menstrual cycle phase may influence performance and injury risk; however, there are few studies in soccer players. Nutrition plays a critical role in health and performance and ensuring adequate energy intake remains a priority. Despite recent progress, there is considerably less research in female than male soccer players. Many gaps in our understanding of how best to develop and manage the health and performance of female soccer players remain.

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BACKGROUND: The most demanding scenarios and physical demands of elite basketball 5-on-5 scrimmages are unknown to trainers, although recent advances in microtechnology allows the gaps in this research to be filled. The purpose of this study was to describe and compare the physical demands, through the most demanding scenarios and traditional average measures, of two different 5-on-5 scrimmage situations executed during training sessions in elite male basketball players. METHODS: Physical demand measures (i.e., total distance covered, high-speed running distance, number of high-intensity accelerations actions, number of high-intensity decelerations actions) were collected from 12 players from the Spanish first Division using a Local Positioning System. Measures were compared via a Bayesian inference analysis, considering playing in half-court (HALF) and half-court and transition (HTRAN) conditions for the 5-on-5 scrimmage. RESULTS: This study showed that, irrespective of the approach used to quantify the physical demands (traditional [average measures per minute] and novel rolling average time epoch [most demanding scenarios]), during the HALF condition players covered less and performed a lower number of high-intensity accelerations and decelerations than in HTRAN (Bayesian factor >10 and standardized effect size >0.6). Furthermore, players' physical demands during 5-on-5 scrimmage situations, independently of the court size, were underestimated consistently by the traditional approach. CONCLUSIONS: Quantifying players' physical demands through the rolling approach may provide a more accurate measure of the most intense periods of activity. Based on the physical demands described, HTRAN may be used to help train players to perform optimally during the most physically-stressful scenarios of match-play whereas HALF may be more suitable to be included in warm-ups, recovery sessions and sessions immediately before a match.

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PURPOSE: Overuse injury risk increases during periods of accelerated growth, which can subsequently impact development in academy soccer, suggesting a need to quantify training exposure. Nonprescriptive development scheme legislation could lead to inconsistent approaches to monitoring maturity and training load. Therefore, this study aimed to communicate current practices of UK soccer academies toward biological maturity and training load. METHODS: Forty-nine respondents completed an online survey representing support staff from male Premier League academies (n = 38) and female Regional Talent Clubs (n = 11). The survey included 16 questions covering maturity and training-load monitoring. Questions were multiple-choice or unipolar scaled (agreement 0-100) with a magnitude-based decision approach used for interpretation. RESULTS: Injury prevention was deemed highest importance for maturity (83.0 [5.3], mean [SD]) and training-load monitoring (80.0 [2.8]). There were large differences in methods adopted for maturity estimation and moderate differences for training-load monitoring between academies. Predictions of maturity were deemed comparatively low in importance for bio-banded (biological classification) training (61.0 [3.3]) and low for bio-banded competition (56.0 [1.8]) across academies. Few respondents reported maturity (42%) and training load (16%) to parent/guardians, and only 9% of medical staff were routinely provided this data. CONCLUSIONS: Although consistencies between academies exist, disparities in monitoring approaches are likely reflective of environment-specific resource and logistical constraints. Designating consistent and qualified responsibility to staff will help promote fidelity, feedback, and transparency to advise stakeholders of maturity-load relationships. Practitioners should consider biological categorization to manage load prescription to promote maturity-appropriate dose-responses and to help reduce the risk of noncontact injury.

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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 (TDist) 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.

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BACKGROUND: Chronic ankle instability (CAI) is linked to mechanical and functional insufficiencies. Joint mobilization is purported to be effective at treating these deficits. PURPOSE: To examine the effect of different treatment durations of a grade IV anterior-to-posterior ankle joint mobilization on weightbearing dorsiflexion range of motion (WB-DFROM), posterior talar glide (PG), and dynamic postural control in individuals with CAI. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 48 female athletes (mean age, 22.8 ± 4.8 years) with unilateral CAI participated in this study. Participants were randomly assigned to 1 of 3 treatment conditions: 30 seconds, 60 seconds, and 120 seconds. Treatment was provided to the injured limb on 3 separate occasions 48 hours apart and consisted of a Maitland grade IV anterior-to-posterior talar joint mobilization based on the participant's initial group assignment. WB-DFROM; PG; and the anterior (ANT), posteromedial (PM), and posterolateral (PL) reach directions of the Star Excursion Balance Test were measured bilaterally before and after each treatment. The uninjured limb acted as a control. Data were analyzed using 2-way mixed-model analyses of variance, and effect sizes were calculated through use of Hedges g. RESULTS: Significant differences were detected after all treatment sessions for all outcome measures (P ≤ .001) and between treatment groups after sessions 1, 2, and 3 for all outcome measures (P ≤ .001). Effect sizes were very large or huge for all treatment groups for WB-DFROM, PG, and ANT reach direction. Substantial variation was found in effect sizes for PM and PL measures. CONCLUSION: Accessory mobilization is an effective treatment to induce acute changes in ankle motion and dynamic postural control in patients with CAI, with longer treatment durations conferring greater improvements. CLINICAL RELEVANCE: This study adds clarity to the use of joint mobilization treatments and will add to the current clinical practice strategy for patients with CAI.

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OBJECTIVES: The purpose of this study was to examine whether the use of machine learning improved the ability of a neuromuscular screen to identify injury risk factors in elite male youth football players. DESIGN: Prospective cohort study. METHODS: 355 elite youth football players aged 10-18 years old completed a prospective pre-season neuromuscular screen that included anthropometric measures of size, as well as single leg countermovement jump (SLCMJ), single leg hop for distance (SLHD), 75% hop distance and stick (75%Hop), Y-balance anterior reach and tuck jump assessment. Injury incidence was monitored over one competitive season. Risk profiling was assessed using traditional regression analyses and compared to supervised machine learning algorithms constructed using decision trees. RESULTS: Using continuous data, multivariate logistic analysis identified SLCMJ asymmetry as the sole significant predictor of injury (OR 0.94, 0.92-0.97, p<0.001), with a specificity of 97.7% and sensitivity of 15.2% giving an AUC of 0.661. The best performing decision tree model provided a specificity of 74.2% and sensitivity of 55.6% with an AUC of 0.663. All variables contributed to the final machine model, with asymmetry in the SLCMJ, 75%Hop and Y-balance, plus tuck jump knee valgus and anthropometrics being the most frequent contributors. CONCLUSIONS: Although both statistical methods reported similar accuracy, logistic regression provided very low sensitivity and only identified a single neuromuscular injury risk factor. The machine learning model provided much improved sensitivity to predict injury and identified interactions of asymmetry, knee valgus angle and body size as contributing factors to an injurious profile in youth football players.

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CONTEXT: Despite the popularity of jump-landing tasks being used to identify injury risk factors, minimal data currently exist examining differences in knee kinematics during commonly used bilateral jumping tasks. This is especially the case for rebounding-based protocols involving young athletes. OBJECTIVE: To compare the frontal plane projection angles (FPPAs) during the drop vertical jump (DVJ) and tuck jump assessment (TJA) in a cohort of elite male youth soccer players of varying maturity status. METHODS: A total of 57 male youth soccer players from an English championship soccer club participated in this study. Participants performed 3 trials of the DVJ and TJA, during which movement was recorded with 2-dimensional video cameras. FPPA for both right (FPPA-r) and left (FPPA-l) legs, with values <180° indicative of medial knee displacement. RESULTS: On a whole-group level, FPPA-r (172.7° [7.4°] vs 177.2° [11.7°]; P < .05; effect size [ES] = 0.46) and FPPA-l (173.4° [7.3°] vs 179.2° [11.0°]; P < .05; ES = 0.62) were significantly greater for both limbs in the TJA compared with the DVJ; however, these differences were less consistent when grouped by maturity status. FPPA-r during the TJA was significantly and moderately greater in the circa-peak height velocity (PHV) group compared with the post-PHV cohorts (169.4° [6.4°] vs 175.3° [7.8°]; P < .05; ES = 0.49). Whole-group data showed moderate relationships for FPPA-r and FPPA-l between the TJA and DVJ; however, stronger relationships were shown in circa- and post-PHV players compared with the pre-PHV cohort. CONCLUSIONS: Considering that the TJA exposed players to a larger FPPA and was sensitive to between-group differences in FPPA-r, the TJA could be viewed as a more suitable screen for identifying FPPA in young male soccer players.

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Read, PJ, Oliver, JL, Croix, MS, Myer, GD, and Lloyd, RS. A review of field-based assessments of neuromuscular control and their utility in male youth soccer players. J Strength Cond Res 33(1): 283-299, 2019-Lower-extremity injuries in male youth soccer are common and equate to a substantial time loss from training and competitions during the course of a season. Extended periods of absence will impact player involvement in skill and physical development activities, as well as participation in competitive match play. Neuromuscular risk factors for lower-extremity injury in male youth soccer players can be categorized into quadriceps dominance, leg dominance, ligament dominance, trunk dominance, and reduced dynamic stability. Valid screening methods to identify risk factors that are practically viable are needed for youth athletes who may be at a greater risk of injury in soccer. Although field-based tests of neuromuscular control provide a reliable option for the assessment of injury risk in adults and females, less data are available in male youth soccer players, and further research is required to examine their ability to predict injury risk. This article provides a review of the current literature pertaining to field-based screening tests and critically appraises their suitability for use with male youth soccer players. Currently, the only method that has been validated in male youth soccer players is the landing error scoring system. Asymmetrical anterior reach measured during the Y-Balance test may also be considered because of its strong predictive ability in male youth basketball players; however, further research is required to fully support its use with soccer players.

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Jeffreys, MA, De Ste Croix, MBA, Lloyd, RS, Oliver, JL, and Hughes, JD. The effect of varying plyometric volume on stretch-shortening cycle capability in collegiate male rugby players. J Strength Cond Res 33(1): 139-145, 2019-The purpose of this study was to identify the effectiveness of low and high volume plyometric loads on developing stretch-shortening cycle capability in collegiate rugby players. A between-group repeated measures design was used. Thirty-six subjects (age 20.3 ± 1.6 years, mass 91.63 ± 10.36 kg, stature 182.03 ± 5.24 cm) were randomly assigned to one of 3 groups: a control group (CG), a low volume plyometric group (LPG), or a high volume plyometric group (HPG). Data were collected from a force plate, and measures of reactive strength index (RSI) and leg stiffness were calculated from jump height, contact time, and flight time. A significant between-group × time (F = 4.01, p ≤ 0.05) interaction effect for RSI was observed. Bonferroni post hoc analysis indicated that both the LPG training group (p = 0.002) and HPG training group (p = 0.009) were significantly higher than the control group. No significant interaction effect between time × group was observed for leg stiffness (F = 1.39, p = 0.25). This study has demonstrated that it is possible to improve reactive strength capabilities through the use of a low volume plyometric program. The low volume program elicited the same performance improvement in RSI as a high volume program while undertaking a lower dose. This suggests that strength and conditioning coaches may be able to benefit from the ability to develop more time-efficient and effective plyometric programs.

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OBJECTIVES: Examine the effects of maturation on single leg jumping performance in elite male youth soccer players. DESIGN: Cross sectional. SETTING: Academy soccer clubs. PARTICIPANTS: 347 male youth players classified as either pre, circa or post-peak height velocity (PHV). MAIN OUTCOME MEASURES: Single leg countermovement jump (SLCMJ) height, peak vertical landing forces (pVGRF), knee valgus and trunk side flexion. RESULTS: Vertical jump height and absolute pVGRF increased with each stage of maturation (p < 0.001; d = 0.85-2.35). Relative to body weight, significantly higher landing forces were recorded on the left leg in circa versus post-PHV players (p < 0.05; d = -0.40). Knee valgus reduced with maturation but the only notable between-group differences were shown in post-PHV players (p < 0.05; d = 0.67); however, greater ipsilateral lateral trunk flexion angles was also present and these differences were significantly increased relative to circa-PHV players (p < 0.05; d = 0.85). CONCLUSION: Periods of rapid growth are associated with landing kinetics which may heighten injury risk. While reductions in knee valgus were displayed with maturation; a compensatory strategy of greater trunk lateral flexion was evident in post-PHV players and this may increase the risk of injury.

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CONTEXT: Despite the high frequency of knee injuries in athletes, few researchers have studied the effects of chronologic age and stage of maturation on knee-joint kinematics in male youth soccer players. OBJECTIVE: To use a coach-friendly screening tool to examine knee-valgus scores for players of different ages and at different stages of maturation. DESIGN: Cross-sectional study. SETTING: Academy soccer clubs. PATIENTS OR OTHER PARTICIPANTS: A total of 400 elite male youth soccer players aged 10 to 18 years categorized by chronologic age and stage of maturation based on their years from peak height velocity (PHV). MAIN OUTCOME MEASURE(S): Knee valgus was evaluated during the tuck-jump assessment via 2-dimensional analysis. Frontal-plane projection angles were subjectively classified as minor (<10°), moderate (10°-20°), or severe (>20°), and using these classifications, we scored knee valgus in the tuck jump as 0 ( no valgus), 1 ( minor), 2 ( moderate), or 3 ( severe). RESULTS: A trend toward higher valgus scores was observed in the younger age groups and the pre-PHV group. The lowest frequency of no valgus occurred in the U18 and post-PHV groups. The highest percentages of severe scores were in the U13 and pre-PHV groups for the right limb. Knee-valgus scores were lower for both lower extremities in the U18 group than in all other age groups ( P < .001) except the U16 group. Scores were lower for the post-PHV than the pre-PHV group for the right limb ( P < .001) and both pre-PHV and circa-PHV groups for the left limb ( P < .001). Noteworthy interlimb asymmetries were evident in the U14, U15, and circa-PHV groups. CONCLUSIONS: Reductions in knee valgus with incremental age and during the later stages of maturation indicated that this risk factor was more prevalent in younger players. Interlimb asymmetry may also emerge around the time of the peak growth spurt and early adolescence, potentially increasing the risk of traumatic injury.

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PURPOSE: Asymmetry is a risk factor for male youth soccer players. There is a paucity of data confirming the presence of asymmetry using practically viable screening tasks in players at different stages of maturation. METHODS: A cross-sectional sample (N = 347) of elite male youth soccer players who were either pre-, circa-, or post-peak height velocity (PHV) completed the following assessments: single-leg Y-Balance anterior reach, single-leg hop for distance, single-leg 75% hop and stick, and single-leg countermovement jumps. RESULTS: Single-leg countermovement jumps landing force asymmetry was higher in both circa- and post-PHV groups (P < .001; d = 0.41-0.43). Single-leg 75% hop and stick landing force asymmetries were also highest in circa-PHV players, but between-group comparisons were not statistically significant and effect sizes were small. Single-leg hop for distance and single-leg Y-Balance anterior reach asymmetries reduced with maturation; however, no group differences were significant, with small to trivial effect sizes (d ≤ 0.25). CONCLUSION: Stage of maturation did not have a profound effect on asymmetry. Between-limb differences in functional performance seem to be established in early childhood; thus, targeted interventions to reduce this injury risk factor should commence in pre-PHV athletes and be maintained throughout childhood and adolescence to ensure asymmetry does not increase.

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Regulations now state that professional academies in the United Kingdom are required to substantially increase the volume of soccer training. This study assessed the current injury occurrence, providing an update to reports published prior to the introduction of the Elite Player Performance Plan (EPPP). 608 soccer players aged 11-18 years from six professional soccer clubs were prospectively monitored, recording injuries during the 2014-2015 season. An injury rate of 1.32 injuries per player/season was indicated with a mean time loss of 21.9 days per injury. The greatest time loss per injury was in the U14s-U15s, and the highest rate of severe injuries in the U15s. Strains and sprains were the most common injury type, with the knee and ankle the most frequently injured anatomical sites. Seasonal variation indicated two peaks in injury incidence, occurring in September and January. In comparison to a published audit prior to the inception of the EPPP, this study indicates that academy soccer players are three-times more likely to experience an injury. Given that time loss and injury severity also increased during periods that typically follow rapid growth, these players should be considered an important group for training load monitoring and injury prevention strategies.

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De Ste Croix, MBA, Hughes, JD, Lloyd, RS, Oliver, JL, and Read, PJ. Leg stiffness in female soccer players: intersession reliability and the fatiguing effects of soccer-specific exercise. J Strength Cond Res 31(11): 3052-3058, 2016-Low levels of leg stiffness and reduced leg stiffness when fatigue is present compromise physical performance and increase injury risk. The purpose of this study was to (a) determine the reliability of leg stiffness measures obtained from contact mat data and (b) explore age-related differences in leg stiffness after exposure to a soccer-specific fatigue protocol in young female soccer players. Thirty-seven uninjured female youth soccer players divided into 3 subgroups based on chronological age (under 13 [U13], under 15 [U15], and under 17 [U17] year-olds) volunteered to participate in the study. After baseline data collection, during which relative leg stiffness, contact time, and flight time were collected, participants completed an age-appropriate soccer-specific fatigue protocol (SAFT). Upon completion of the fatigue protocol, subjects were immediately retested. Intersession reliability was acceptable and could be considered capable of detecting worthwhile changes in performance. Results showed that leg stiffness decreased in the U13 year-olds, was maintained in the U15 age group, and increased in the U17 players. Contact times and flight times did not change in the U13 and U15 year-olds, but significantly decreased and increased, respectively, in the U17 age group. The data suggest that age-related changes in the neuromuscular control of leg stiffness are present in youth female soccer players. Practitioners should be aware of these discrepancies in neuromuscular responses to soccer-specific fatigue, and should tailor training programs to meet the needs of individuals, which may subsequently enhance performance and reduce injury risk.

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Quantifying hopping and landing performances can assist coaches in identifying young male soccer players who may be at increased risk of injury. The influence of chronological age and maturation on these measures in this population is unknown. Single leg hop for distance (SLHD) and 75% horizontal hop and stick landing force (75%Hop) were examined in a cross-sectional sample (N=400) of elite male youth soccer players. Between-group differences for both chronological age (U11-U18) and stage of maturation (pre-, circa- or post-peak height velocity (PHV)) were analyzed. Absolute 75%Hop increased with both age and maturation. Apart from the U18s, pre-PHV and U11-U12 players displayed the greatest relative landing forces compared to all other groups (p<0.001; d=0.56-0.93). Absolute and relative SLHD were greatest in the U18s and post-PHV players (p<0.001; d=0.35-2.04). A trend showed increased SLHD with each consecutive age group although a reduction in performance was identified in the U13s (d=0.50-0.59). High volumes of accumulated soccer participation in the U18s may lead to altered landing strategies indicative of high injury risk. A temporary reduction in hop performance in the U13s may also be linked to a period of adolescent awkwardness.

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PURPOSE: The purpose of this study was to investigate the influence of exercise intensity on postexercise supine and tilt baroreflex sensitivity (BRS). METHOD: Nine healthy, active men performed 2 conditions of interval cycling of 40% maximal work rate (WRmax) and 75% WRmax of matched work done and a control condition of no exercise in a counterbalanced order. BRS outcome measures were determined at preexercise and postexercise up to +24 hr in supine and tilt positions. R-R interval and blood pressure data were collected over consecutive 10-min periods and were analyzed by Fast Fourier transformation analysis. RESULTS: A fully repeated analysis of variance revealed a significant interaction (p < .05) between time and condition in supine for BRSαLF, F(3, 134) = 5.19, p < .05, ES = .39, and BRSTFTG, F(3, 134) = 5.65, p < .05, ES = .41, and in tilt for BRSUpUp, F(3, 134) = 3.54, p < .05, ES = .31, BRSDownDown, F(3, 134) = 5.94, p < .05, ES = .43, BRSαLF, F(4, 134) = 6.23, p < .05, ES = .44, and BRSTFTG, F(4, 134) = 9.22, p < .05, ES = .54. There were significant differences (p < .05) between condition comparisons at +15 min and between control and 75% WRmax and between the 40% WRmax and 75% WRmax conditions at +60 min. At +15 min, BRS was lower in the 75% WRmax condition compared with the 40% WRmax condition and the control condition, and it was lower in the 40% WRmax condition than in the control condition. CONCLUSION: The findings demonstrate an intensity-dependent relationship in the BRS response following exercise.

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Early specialisation is characterised by formal participation in a single sport at the exclusion of others. Limited data are available to support this approach in the development of soccer players who attain elite status later in life. Of growing concern is the associated increased risk of injury and suggestions that single sport specialisation is a risk factor independent of age, growth, biological maturation and training volumes. In the United Kingdom, elite soccer organisations have recently adopted an early sport specialisation approach following the introduction of the Elite Player Performance Plan. A key tenet of this programme is increased opportunities for training through a marked rise in the specified on-pitch hours per week. The accumulation of high training hours may be less of a relevant marker for success, and the impact of such a significant increase in training volume for young athletes who are experiencing a range of growth and maturational processes is currently unknown. This critical commentary includes an evidence-based discussion of the effectiveness of early sport specialisation and the potential injury risks associated with such programmes placing a specific focus on elite male youth soccer players. Available data indicate that modifications to the existing Elite Player Performance Plan framework could enhance players' development and reduce injury risk. Proposed alterations include reduced volume of soccer-specific training at key stages of growth and maturation and guidelines for the provision of a greater variety of physical activities that are integrated within other programme components.

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Injuries reported in male youth soccer players most commonly occur in the lower extremities, and include a high proportion of ligament sprains at the ankle and knee with a lower proportion of overuse injuries. There is currently a paucity of available literature that examines age- and sex-specific injury risk factors for such injuries within youth soccer players. Epidemiological data have reported movements that lead to non-contact ligament injury include running, twisting and turning, over-reaching and landing. Altered neuromuscular control during these actions has been suggested as a key mechanism in females and adult populations; however, data available in male soccer players is sparse. The focus of this article is to review the available literature and elucidate prevalent risk factors pertaining to male youth soccer players which may contribute to their relative risk of injury.

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