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Background: Young athletes who specialize early in a single sport may subsequently be at increased risk of injury. While heightened injury risk has been theorized to be related to volume or length of exposure to a single sport, the development of unhealthy, homogenous movement patterns, and rigid neuromuscular control strategies may also be indicted. Unfortunately, traditional laboratory assessments have limited capability to expose such deficits due to the simplistic and constrained nature of laboratory measurement techniques and analyses., Methods: To overcome limitations of prior studies, the authors proposed a soccer-specific virtual reality header assessment to characterize the generalized movement regularity of 44 young female athletes relative to their degree of sport specialization (high vs low). Participants also completed a traditional drop vertical jump assessment., Results: During the virtual reality header assessment, significant differences in center of gravity sample entropy (a measure of movement regularity) were present between specialized (center of gravity sample entropy: mean = 0.08, SD = 0.02) and nonspecialized center of gravity sample entropy: mean = 0.10, SD = 0.03) groups. Specifically, specialized athletes exhibited more regular movement patterns during the soccer header than the nonspecialized athletes. However, no significant between-group differences were observed when comparing participants' center of gravity time series data from the drop vertical jump assessment., Conclusions: This pattern of altered movement strategy indicates that realistic, sport-specific virtual reality assessments may be uniquely beneficial in exposing overly rigid movement patterns of individuals who engage in repeated sport specialized practice.

Abstract: Pedley, JS, Lloyd, RS, Read, PJ, Moore, IS, Myer, GD, and Oliver, JL. A novel method to categorize stretch-shortening cycle performance across maturity in youth soccer players. J Strength Cond Res 36(9): 2573-2580, 2022-This study used a novel method to categorize stretch-shortening cycle (SSC) function during a drop jump (DJ) using the force-time curve. This method was then used to determine the effect of maturity status upon SSC function and effect of SSC function on DJ performance. Prepeak, circa-peak, and postpeak height velocity male youth soccer players completed a preseason 30-cm DJ onto a force plate. Stretch-shortening cycle function was categorized as poor (impact peak and not spring-like), moderate (impact peak and spring-like), or good (no impact peak and spring-like). Interactions between SSC function and maturity status, and SSC function and kinetic variables were explored. Youth soccer players displaying good SSC function were older and more mature than those with poor SSC function; however, 9.9% of post peak height velocity still displayed poor SSC function. Players with good SSC function recorded significantly shorter ground contact times, reduced time between peak landing and takeoff force, reduced center of mass displacement, and significantly greater takeoff forces than players with moderate and poor SSC function (all p < 0.05). SSC function during a standardized DJ improves with maturation, but a portion of mature players still demonstrate poor SSC function. Good SSC function was associated with improved DJ outcome measures except jump height. Tailored training interventions based on SSC competency may be required to optimally enhance SSC function., (Copyright © 2020 National Strength and Conditioning Association.)

Cumulative exposure to head impacts during contact sports can elicit potentially deleterious brain white matter alterations in young athletes. Head impact exposure is commonly quantified using wearable sensors; however, these sensors tend to overestimate the number of true head impacts that occur and may obfuscate potential relationships with longitudinal brain changes. The purpose of this study was to examine whether data-driven filtering of head impact exposure using machine learning classification could produce more accurate quantification of exposure and whether this would reveal more pronounced relationships with longitudinal brain changes. Season-long head impact exposure was recorded for 22 female high school soccer athletes and filtered using three methods-threshold-based, heuristic filtering, and machine learning (ML) classification. The accuracy of each method was determined using simultaneous video recording of a subset of the sensor-recorded impacts, which was used to confirm which sensor-recorded impacts corresponded with true head impacts and the ability of each method to detect the true impacts. Each filtered dataset was then associated with the athletes' pre- and post-season MRI brain scans to reveal longitudinal white matter changes. The threshold-based, heuristic, and ML approaches achieved 22.0% accuracy, 44.6%, and 83.5% accuracy, respectively. ML classification also revealed significant longitudinal brain white matter changes, with negative relationships observed between head impact exposure and reductions in mean and axial diffusivity and a positive relationship observed between exposure and fractional anisotropy (all p < 0.05).

Objectives: Examine growth and maturation trends in dynamic balance using the anterior reach Y-Balance test, and its utility as an injury risk screening tool., Design: Cross sectional and prospective cohort., Setting: Elite male youth soccer players., Participants: 346 players grouped as pre, circa or post peak height velocity (PHV)., Main Outcome Measures: Pre-season anterior reach absolute and relative Y-Balance test scores and seasonal prospective lower extremity injury monitoring., Results: Absolute reach distances were greatest post-PHV (p < 0.05). Relative to leg length, pre-PHV achieved the highest scores and increased between-limb differences. Significant associations between injury and anterior reach scores were present in pre (OR: 0.94, CI: 0.91-0.98, p < 0.05) and circa-PHV (OR: 1.05, 95% CI: 1.05-1.10, p < 0.05). Increased age (OR: 1.49, 95% CI: 1.04-2.13, p < 0.05) and height (OR: 1.06, 95% CI: 0.99-1.13, p = 0.82) were risk factors post-PHV. No differences in injury occurrence were shown between players with absolute reach difference >4 cm in any group., Conclusions: Anterior reach scores increased injury risk, but associations were small and inconsistent. The Y-Balance should be used with caution as a screening tool in this cohort., Competing Interests: Declaration of competing interest Paul J. Read, Jon L. Oliver, Gregory D. Myer, PhD, Abdulaziz Farooq, Mark De Ste Croix, and Rhodri S. Lloyd confirm there are no conflicts of interest associated with any aspects or content of this manuscript., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Background: Characterization of, and evaluation of strategies to mitigate, the effects of sub-concussive impacts (SCI) on brain structure and function are crucial to understanding potential long-term neurological risks associated with sports participation. Objectives: To evaluate the efficacy of a jugular vein compression collar for preserving functional and structural measures of brain network organization in a cohort of female high school soccer players throughout a season of competitive play. Methods: Athletes were assigned to a collar ( N  = 72) or non-collar ( N  = 56) group before engaging in a season of play, during which head impact data were recorded via accelerometer for every practice and competition. Participants completed neuroimaging sessions before and following the season. A graph theoretical framework was applied to the functional and structural connectivity measures computed from resting state functional magnetic resonance imaging (rs-fMRI) and diffusion tensor imaging (DTI) data. Results: Non-collar-wearing athletes exhibited significantly increased rs-fMRI-derived global clustering coefficients ( p  = 0.032) and DTI-derived modularity ( p  = 0.042), compared to collar-wearing athletes. No longitudinal changes in any graph measures were observed for the collar group ( p  > 0.05). Conclusion: The observed increase in graph measures in the non-collar group is congruent with previous studies of SCI and is similar to graph theoretical studies of traumatic brain injury. The absence of alterations in graph metrics in the collar group indicates a potential ameliorating effect of the collar device against network reorganization, in line with previous literature.

Objective: We performed a systematic review and meta-analysis of epidemiological data of injuries in professional male football., Method: Forty-four studies have reported the incidence of injuries in football. Two reviewers independently extracted data and assessed trial quality using the Strengthening the Reporting of Observational Studies in Epidemiology statement and Newcastle Ottawa Scale. Studies were combined in a pooled analysis using a Poisson random effects regression model., Results: The overall incidence of injuries in professional male football players was 8.1 injuries/1000 hours of exposure. Match injury incidence (36 injuries/1000 hours of exposure) was almost 10 times higher than training injury incidence rate (3.7 injuries/1000 hours of exposure). Lower extremity injuries had the highest incidence rates (6.8 injuries/1000 hours of exposure). The most common types of injuries were muscle/tendon (4.6 injuries/1000 hours of exposure), which were frequently associated with traumatic incidents. Minor injuries (1-3 days of time loss) were the most common. The incidence rate of injuries in the top 5 European professional leagues was not different to that of the professional leagues in other countries (6.8 vs 7.6 injuries/1000 hours of exposure, respectively)., Conclusions: Professional male football players have a substantial risk of sustaining injuries, especially during matches., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2020. No commercial re-use. See rights and permissions. Published by BMJ.)

Context: Laboratory-based biomechanical analyses of sport-relevant movements such as landing and cutting have classically been used to quantify kinematic and kinetic factors in the context of injury risk, which are then used to inform targeted interventions designed to improve risky movement patterns during sport. However, the noncontextual nature of standard assessments presents challenges for assessing sport-relevant skill transfer., Objective: To examine injury-risk biomechanical differences exhibited by athletes during a jump-landing task performed as part of both a standard biomechanical assessment and a simulated, sport-specific virtual reality (VR)-based assessment., Design: Observational study., Setting: Medical center laboratory., Participants: Twenty-two female adolescent soccer athletes (age = 16.0 [1.4] y, height = 165.6 [4.9] cm, and weight = 60.2 [11.4] kg)., Interventions: The landing performance was analyzed for a drop vertical jump task and a VR-based, soccer-specific corner-kick scenario in which the athletes were required to jump to head a virtual soccer ball and land., Main Outcome Measures: Hip, knee, and ankle joint kinematic differences in the frontal and sagittal planes., Results: Athletes exhibited reduced hip and ankle flexion, hip abduction, and frontal plane ankle excursion during landing in realistic sport scenario compared with the standard drop vertical jump task., Conclusion: VR-based assessments can provide a sport-specific context in which to assess biomechanical deficits that predispose athletes for lower-extremity injury and offer a promising approach to better evaluate skill transfer to sport that can guide future injury prevention efforts.

Objective: Determine how lower limb neuromuscular control changes over the course of a competitive soccer season., Design: Repeated measures., Setting: Academy soccer club., Participants: 43 male youth soccer players (age 13.1 ± 2.2 yr; height 160.1 ± 15.7 cm; body mass 49.4 ± 14.3 kg; maturity offset 0.2 ± 1.9 yr)., Main Outcome Measures: Pre-, mid- and end of season assessments of peak landing forces during single leg 75% horizontal hop and stick (75%HOP) and a single leg countermovement jump (SLCMJ), single leg hop for distance (SLHD), knee valgus during the tuck jump assessment (TJA) and inter-limb symmetries., Results: Hop distance increased significantly. Absolute peak landing forces in the left leg during the SLCMJ and 75%HOP increased significantly, with significant increases also present in the same leg for SLCMJ relative peak landing force. TJA knee valgus score was reduced in the right leg, but remained at a 'moderate' level in the left knee., Conclusion: Neuromuscular control, as evidenced by increased absolute and relative peak landing forces, appears to reduce over the course of a competitive season. Young soccer players should engage in neuromuscular training throughout the season to offset any decrements in neuromuscular control and to facilitate appropriate landing strategies., Competing Interests: Declaration of competing interest None declared., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Purpose: To (1) quantify white matter (WM) alterations in female high school athletes during a soccer season and characterise the potential for normalisation during the off-season rest period, (2) determine the association between WM alterations and exposure to repetitive subconcussive head impacts, and (3) evaluate the efficacy of a jugular vein compression collar to prevent WM alterations associated with head impact exposure., Methods: Diffusion tensor imaging (DTI) data were prospectively collected from high school female soccer participants (14-18 years) at up to three time points over 9 months. Head impacts were monitored using accelerometers during all practices and games. Participants were assigned to a collar (n=24) or non-collar group (n=22). The Tract-Based Spatial Statistics approach was used in the analysis of within-group longitudinal change and between-group comparisons., Results: DTI analyses revealed significant pre-season to post-season WM changes in the non-collar group in mean diffusivity (2.83%±2.46%), axial diffusivity (2.58%±2.34%) and radial diffusivity (3.52%±2.60%), but there was no significant change in the collar group despite similar head impact exposure. Significant correlation was found between head impact exposure and pre-season to post-season DTI changes in the non-collar group. WM changes in the non-collar group partially resolved at 3 months off-season follow-up., Discussion: Microstructural changes in WM occurred during a season of female high school soccer among athletes who did not wear the collar device. In comparison, there were no changes in players who wore the collar, suggesting a potential prophylactic effect of the collar device in preventing changes associated with repetitive head impacts. In those without collar use, the microstructural changes showed a reversal towards normal over time in the off-season follow-up period., Competing Interests: Competing interests: DS is the inventor of the Q-Collar approach and has financial interest in the results of the current research. One author (GDM) consults for Q30 Innovations to support applications with the US Food and Drug Administration but has no financial interest in the commercialization of the Q-Collar. Q30 Sports Sciences has financial interests in the development of the Q-Collar., (© Author(s) (or their employer(s)) 2019. No commercial re-use. See rights and permissions. Published by BMJ.)

Objective: To estimate the incidence proportion (IP) and incidence rate (IR) of ACL injury in football players., Design: Systematic review with meta-analysis., Data Sources: PubMed, CINAHL and SPORTDiscus electronic databases were searched from inception to 20 January 2017., Eligibility Criteria for Selecting Study: Studies that reported the total number of participants/population by sex, total number of ACL injuries by sex and total person-time by sex were included., Results: Twenty-eight studies were included. The IP and IR of ACL injury in female football players were 2.0% (95% CI 1.2% to 3.1%) and 2.0/10 000 athlete exposures (AEs) (95% CI 1.6 to 2.6; I 2 =91%) over a period of one season to 4 years. The IP and IR of ACL injury in male players were 3.5% (95% CI 0.7% to 8.2%) and 0.9/10 000 AEs (95% CI 0.7 to 1.1; I 2 =94%). Studies that evaluated matched cohorts of female and male players showed no difference in IP (relative risk=1.2; 95% CI 0.9 to 1.6; P=0.47) over a period of one season to 4 years. Women were at greater risk than men (incidence rate ratio (IRR)=2.2; 95% CI 1.6 to 3.1; I 2 =83%; P<0.001). When accounting for participation level, the difference in IR between women and men was greatest for intermediate players (IRR=2.9; 95% CI 2.4 to 3.6) compared with amateur (IRR=2.6; 95% CI 1.4 to 4.8) and elite (IRR=2.0; 95% CI 1.1 to 3.4) players., Summary/conclusion: Overall, more men sustained ACL injury in football. There was no difference in the relative risk of ACL injury between female and male football players in a window that spanned one season to 4 years. The IR of ACL injury among women was 2.2 times higher than the IR of ACL injury among men. The reported sex disparity in ACL injury was independent of participation level., Competing Interests: Competing interests: None declared., (© Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2019. All rights reserved. No commercial use is permitted unless otherwise expressly granted.)

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.

Context: Early sport specialization, or the participation in 1 sport year-round to the exclusion of all others, is a growing concern in youth athletics because of its possible association with musculoskeletal injury. The underlying injury risk may be the result of coordination differences that sport-specialized athletes have been speculated to exhibit relative to multisport athletes; however, little evidence exists to support or refute this notion., Objective: To examine relative hip- and knee-joint angular-motion variability among adolescent sport-specialized and multisport female adolescent athletes to determine how sport specialization may affect coordination., Design: Cohort study., Setting: Research laboratory., Patients or Other Participants: A total of 366 sport-specialized and 366 multisport adolescent female basketball, soccer, and volleyball players., Intervention(s): Drop-vertical-jump (DVJ) assessment., Main Outcome Measure(s): Average coupling-angle variability (CAV) for hip flexion and knee flexion, knee flexion and ankle flexion, hip flexion and knee abduction, knee flexion and knee abduction, knee flexion and knee internal rotation, and knee abduction and knee internal rotation., Results: The sport-specialized group exhibited increased coupling variability in dominant-limb hip flexion and knee flexion ( P = .015), knee flexion and knee abduction ( P = .014), and knee flexion and knee internal rotation ( P = .048) while landing during the DVJ, although they had small effect sizes (η 2 = 0.010, 0.010, and 0.007, respectively). No differences were present between groups for any of the other CAV measures of the dominant limb, and no differences were found for any CAV measures of the nondominant limb (all P values > .05)., Conclusions: Sport specialization was associated with increased variability of critical hip- and knee-joint couplings responsible for effective landing during the DVJ. Altered coordination strategies that involve the hip and knee joints may underlie unstable landings, inefficient force-absorption strategies, or greater contact forces that can place the lower extremities at risk for injury (or a combination of these).

Hamstring strain injury (HSI) is one of the most prevalent and severe injury in professional soccer. The purpose was to analyze and compare the predictive ability of a range of machine learning techniques to select the best performing injury risk factor model to identify professional soccer players at high risk of HSIs. A total of 96 male professional soccer players underwent a pre-season screening evaluation that included a large number of individual, psychological and neuromuscular measurements. Injury surveillance was prospectively employed to capture all the HSI occurring in the 2013/2014 season. There were 18 HSIs. Injury distribution was 55.6% dominant leg and 44.4% non-dominant leg. The model generated by the SmooteBoostM1 technique with a cost-sensitive ADTree as the base classifier reported the best evaluation criteria (area under the receiver operating characteristic curve score=0.837, true positive rate=77.8%, true negative rate=83.8%) and hence was considered the best for predicting HSI. The prediction model showed moderate to high accuracy for identifying professional soccer players at risk of HSI during pre-season screenings. Therefore, the model developed might help coaches, physical trainers and medical practitioners in the decision-making process for injury prevention., Competing Interests: The authors declare no conflict of interest., (© Georg Thieme Verlag KG Stuttgart · New York.)

Objectives: We aimed to present a unique prospective neurological dataset for participants who experienced an ACL injury., Design: Prospective longitudinal case-control., Methods: High school female soccer athletes were evaluated using functional magnetic resonance imaging to capture resting-state brain connectivity prior to their competitive season. Two of these athletes later experienced an ACL injury (ACLI). We matched these ACLI participants with eight teammates who did not go on to sustain an ACL injury (uninjured controls, Con) based on age, grade, sex, height, and weight to examine differences in preseason connectivity. Knee-motor regions of interest (ROIs) were created based on previously published data from which five specific areas were selected as seeds for analysis. Independent-samples t-tests with a false discovery rate correction for multiple comparisons determined differences in connectivity between the ACLI and Con., Results: There was significantly greater connectivity between the left primary sensory cortex (a brain region responsible for proprioception) and the right posterior lobe of the cerebellum (a brain region responsible for balance and coordination) for the Con relative to ACLI, t (8)=4.53, p=0.03 (false discovery rate corrected)., Conclusions: These preliminary data indicate that those who do not later sustain an ACL injury exhibit a stronger functional connection between a cortical sensory-motor region and a cerebellar region responsible for balance and coordination. These findings may help to guide development of brain-driven biofeedback training that optimizes and promotes adaptive neuroplasticity to reduce motor coordination errors and injury risk., (Copyright © 2018 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.)

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.

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., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

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.

Recent neuroimaging studies have suggested that repetitive subconcussive head impacts, even after only one sport season, may lead to pre- to post-season structural and functional alterations in male high school football athletes. However, data on female athletes are limited. In the current investigation, we aimed to (1) assess the longitudinal pre- to post-season changes in functional MRI (fMRI) of working memory and working memory performance, (2) quantify the association between the pre- to post-season change in fMRI of working memory and the exposure to head impact and working memory performance, and (3) assess whether wearing a neck collar designed to reduce intracranial slosh via mild compression of the jugular veins can ameliorate the changes in fMRI brain activation observed in the female high school athletes who did not wear collars after a full soccer season. A total of 48 female high school soccer athletes (age range: 14.00-17.97 years) were included in the study. These athletes were assigned to the non-collar group (n = 21) or to the collar group (n = 27). All athletes undewent MRI at both pre-season and post-season. In each session, a fMRI verbal N-Back task was used to engage working memory. A significant pre- to post-season increase in fMRI blood oxygen level dependent (BOLD) signal was demonstrated when performing the N-back working memory task in the non-collar group but not in the collar group, despite the comparable exposure to head impacts during the season between the two groups. The collar group demonstrated significantly smaller pre- to post-season change in fMRI BOLD signal than the non-collar group, suggesting a potential protective effect from the collar device. Significant correlations were also found between the pre- to post-season increase in fMRI brain activation and the decrease in task accuracy in the non-collar group, indicating an association between the compensatory mechanism in underlying neurophysiology and the alteration in the behavioral outcomes.

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.

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.

Context:   An estimated 40 million school-aged children (age range = 5-18 years) participate annually in sports in the United States, generating approximately 4 million sport-related injuries and requiring 2.6 million emergency department visits at a cost of nearly $2 billion., Objective:   To determine the effects of a school-based neuromuscular training (NMT) program on sport-related injury incidence across 3 sports at the high school and middle school levels, focusing particularly on knee and ankle injuries., Design:   Randomized controlled clinical trial., Setting:   A total of 5 middle schools and 4 high schools in a single-county public school district., Patients or Other Participants:   A total of 474 girls (222 middle school, 252 high school; age = 14.0 ± 1.7 years, height = 161.0 ± 8.1 cm, mass = 55.4 ± 12.2 kg) were cluster randomized to an NMT (CORE; n = 259 athletes) or sham (SHAM; n = 215 athletes) intervention group by team within each sport (basketball, soccer, and volleyball)., Intervention(s):   The CORE intervention consisted of exercises focused on the trunk and lower extremity, whereas the SHAM protocol consisted of resisted running using elastic bands. Each intervention was implemented at the start of the season and continued until the last competition. An athletic trainer evaluated athletes weekly for sport-related injuries. The coach recorded each athlete-exposure (AE), which was defined as 1 athlete participating in 1 coach-directed session (game or practice)., Main Outcome Measure(s):   Injury rates were calculated overall, by sport, and by competition level. We also calculated rates of specific knee and ankle injuries. A mixed-model approach was used to account for multiple injuries per athlete., Results:   Overall, the CORE group reported 107 injuries (rate = 5.34 injuries/1000 AEs), and the SHAM group reported 134 injuries (rate = 8.54 injuries/1000 AEs; F 1,578 = 18.65, P < .001). Basketball (rate = 4.99 injuries/1000 AEs) and volleyball (rate = 5.74 injuries/1000 AEs) athletes in the CORE group demonstrated lower injury incidences than basketball (rate = 7.72 injuries/1000 AEs) and volleyball (rate = 11.63 injuries/1000 AEs; F 1,275 = 9.46, P = .002 and F 1,149 = 11.36, P = .001, respectively) athletes in the SHAM group. The CORE intervention appeared to have a greater protective effect on knee injuries at the middle school level (knee-injury incidence rate = 4.16 injuries/1000 AEs) than the SHAM intervention (knee-injury incidence rate = 7.04 injuries/1000 AEs; F 1,261 = 5.36, P = .02). We did not observe differences between groups for ankle injuries ( F 1,578 = 1.02, P = .31)., Conclusions:   Participation in an NMT intervention program resulted in a reduced injury incidence relative to participation in a SHAM intervention. This protective benefit of NMT was demonstrated at both the high school and middle school levels.

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., Competing Interests: Conflict of Interest: The authors have no conflict of interest to declare., (© Georg Thieme Verlag KG Stuttgart · New York.)

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.

Read, P, Oliver, JL, Croix, MD, Myer, GD, and Lloyd, RS. Consistency of field-based measures of neuromuscular control using force-plate diagnostics in elite male youth soccer players. J Strength Cond Res 30(12): 3304-3311, 2016-Deficits in neuromuscular control during movement patterns such as landing are suggested pathomechanics that underlie sport-related injury. A common mode of assessment is measurement of landing forces during jumping tasks; however, these measures have been used less frequently in male youth soccer players, and reliability data are sparse. The aim of this study was to examine the reliability of a field-based neuromuscular control screening battery using force-plate diagnostics in this cohort. Twenty-six pre-peak height velocity (PHV) and 25 post-PHV elite male youth soccer players completed a drop vertical jump (DVJ), single-leg 75% horizontal hop and stick (75%HOP), and single-leg countermovement jump (SLCMJ). Measures of peak landing vertical ground reaction force (pVGRF), time to stabilization, time to pVGRF, and pVGRF asymmetry were recorded. A test-retest design was used, and reliability statistics included change in mean, intraclass correlation coefficient, and coefficient of variation (CV). No significant differences in mean score were reported for any of the assessed variables between test sessions. In both groups, pVGRF and asymmetry during the 75%HOP and SLCMJ demonstrated largely acceptable reliability (CV ≤ 10%). Greater variability was evident in DVJ pVGRF and all other assessed variables, across the 3 protocols (CV range = 13.8-49.7%). Intraclass correlation coefficient values ranged from small to large and were generally higher in the post-PHV players. The results of this study suggest that pVGRF and asymmetry can be reliably assessed using a 75%HOP and SLCMJ in this cohort. These measures could be used to support a screening battery for elite male youth soccer players and for test-retest comparison.

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.

Read, PJ, Oliver, JL, de Ste Croix, MBA, Myer, GD, and Lloyd, RS. Reliability of the tuck jump injury risk screening assessment in elite male youth soccer players. J Strength Cond Res 30(6): 1510-1516, 2016-Altered neuromuscular control has been suggested as a mechanism for injury in soccer players. Ligamentous injuries most often occur during dynamic movements, such as decelerations from jump-landing maneuvers where high-risk movement patterns are present. The assessment of kinematic variables during jump-landing tasks as part of a preparticipation screen is useful in the identification of injury risk. An example of a field-based screening tool is the repeated tuck jump assessment. The purpose of this study was to analyze the within-subject variation of the tuck jump screening assessment in elite male youth soccer players. Twenty-five pre-peak height velocity (PHV) and 25 post-PHV elite male youth soccer players from the academy of a professional English soccer club completed the assessment. A test-retest design was used to explore the within-subject intersession reliability. Technique was graded retrospectively against the 10-point criteria set out in the screening protocol using two-dimensional video cameras. The typical error range reported for tuck jump total score (0.90-1.01 in pre-PHV and post-PHV players respectively) was considered acceptable. When each criteria was analyzed individually, kappa coefficient determined that knee valgus was the only criterion to reach substantial agreement across the two test sessions for both groups. The results of this study suggest that although tuck jump total score may be reliably assessed in elite male youth soccer players, caution should be applied in solely interpreting the composite score due to the high within-subject variation in a number of the individual criteria. Knee valgus may be reliably used to screen elite youth male soccer players for this plyometric technique error and for test-retest comparison.

Context: Biofeedback training enables an athlete to alter biomechanical and physiological function by receiving biomechanical and physiological data concurrent with or immediately after a task., Objective: To compare the effects of 2 different modes of real-time biofeedback focused on reducing risk factors related to anterior cruciate ligament injury., Design: Randomized crossover study design., Setting: Biomechanics laboratory and sports medicine center., Participants: Female high school soccer players (age 14.8 ± 1.0 y, height 162.6 ± 6.8 cm, mass 55.9 ± 7.0 kg; n = 4)., Intervention: A battery of kinetic- or kinematic-based real-time biofeedback during repetitive double-leg squats., Main Outcome Measures: Baseline and posttraining drop vertical jumps were collected to determine if either feedback method improved high injury risk landing mechanics., Results: Maximum knee abduction moment and angle during the landing was significantly decreased after kinetic-focused biofeedback (P = .04). The reduced knee abduction moment during the drop vertical jumps after kinematic-focused biofeedback was not different (P = .2). Maximum knee abduction angle was significantly decreased after kinetic biofeedback (P < .01) but only showed a trend toward reduction after kinematic biofeedback (P = .08)., Conclusions: The innovative biofeedback employed in the current study reduced knee abduction load and posture from baseline to posttraining during a drop vertical jump.

Objectives: To determine if sport specialization increases the risk of anterior knee pain in adolescent female athletes., Design: Retrospective cohort epidemiology study., Methods: Female basketball, soccer, and volleyball players (N = 546) were recruited from a single county public school district in Kentucky consisting of 5 middle schools and 4 high schools. A total of 357 multisport and 189 single-sport (66 basketball, 57 soccer, and 66 volleyball) athlete subjects were included due to their diagnosis of patellofemoral pain (PFP) on physical exam. Testing consisted of a standardized history and physician-administered physical examination to determine the presence of PFP. This study compared self-reported multisport athletes with sport-specialized athletes participating in only 1 sport. The sports-participation data were normalized by sport season, with each sport accounting for 1 season of exposure. Incidence rate ratios and 95% confidence intervals (CI) were calculated and used to determine significant differences between athletes who specialized in sport in early youth and multisport athletes., Results: Specialization in a single sport increased the relative risk of PFP incidence 1.5-fold (95% CI 1.0-2.2, P = .038) for cumulative PFP diagnoses. Specific diagnoses such as Sinding Larsen Johansson/ patellar tendinopathy (95% CI 1.5-10.1, P = .005) and Osgood Schlatter disease (95% CI 1.5-10.1, P = .005) demonstrated a 4-fold greater relative risk in single-sport compared with multisport athletes. Incidence of other specific PFP diagnoses such as fat pad, plica, trauma, pes anserine bursitis, and iliotibial-band tendonitis was not different between single-sport and multisport participants (P > .05)., Conclusion: Early sport specialization in female adolescents is associated with increased risk of anterior knee-pain disorders including PFP, Osgood Schlatter, Sinding Larsen-Johansson compared with multisport athletes.

The purpose of this study was to examine relationships between functional movement screen scores, maturation and physical performance in young soccer players. Thirty males (11-16 years) were assessed for maturation, functional movement screen scores and a range of physical performance tests (squat jump, reactive strength index protocol and reactive agility cut). Older players significantly outperformed younger participants in all tests (P < 0.05; effect sizes = 1.25-3.40). Deep overhead squat, in-line lunge, active straight leg raise and rotary stability test were significantly correlated to all performance tests. In-line lunge performance explained the greatest variance in reactive strength index (adjusted R(2) = 47%) and reactive agility cut (adjusted R(2) = 38%) performance, whilst maturation was the strongest predictor of squat jump performance (adjusted R(2) = 46%). This study demonstrated that variation of physical performance in youth soccer players could be explained by a combination of both functional movement screen scores and maturation.

Objective: The purpose of this study was to examine the association of knee injuries with subsequent changes in body mass index and body composition during maturation in young females., Methods: A prospective longitudinal study design was employed to evaluate young females active in soccer or basketball (N=862). Participants who completed at least 1-year follow-up to provide consecutive annual measures of BMIZ and %fat were included in the study analysis to determine the effect of knee injuries on the trajectory of these obesity markers in youth., Results: Of the 71 reported knee injuries, 12 (17%) occurred in athletes at the prepubertal stage, 24 (34%) in athletes at the pubertal stage, and 35 (49%) in postpubertal athletes. Controlling for the effects of maturation, female athletes who reported knee injury demonstrated a greater yearly increase in BMIZ (LS means and 95% CI for the injured group=0.039 (-0.012 to 0.089), for the non-injured group=-0.019 (-0.066 to 0.029), and group difference=0.057 (0.005 to 0.11), p=0.03) and in %body fat (LS means and 95% CI for the injured group=1.05 (0.45 to 1.65), for the non-injured group=0.22 (-0.21 to 0.064), and group difference=0.83 (0.21 to 1.45), p=0.009), compared to those without knee injuries. This indicates that the athletes with knee injuries will increase their body mass index percentile by up to 5 units more than someone of the same age without an injury, and in body fat by up to 1.5%, compared to their non-injured peers., Conclusions: The present findings indicate that knee injury during the growing years may be associated with unfavourable changes in body composition., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.)

Context: Prospective measures of high external knee-abduction moment (KAM) during landing identify female athletes at increased risk of patellofemoral pain (PFP). A clinically applicable screening protocol is needed., Objective: To identify biomechanical laboratory measures that would accurately quantify KAM loads during landing that predict increased risk of PFP in female athletes and clinical correlates to laboratory-based measures of increased KAM status for use in a clinical PFP injury-risk prediction algorithm. We hypothesized that we could identify clinical correlates that combine to accurately determine increased KAM associated with an increased risk of developing PFP., Design: Descriptive laboratory study., Setting: Biomechanical laboratory., Patients or Other Participants: Adolescent female basketball and soccer players (n = 698) from a single-county public school district., Main Outcome Measure(s): We conducted tests of anthropometrics, maturation, laxity, flexibility, strength, and landing biomechanics before each competitive season. Pearson correlation and linear and logistic regression modeling were used to examine high KAM (>15.4 Nm) compared with normal KAM as a surrogate for PFP injury risk., Results: The multivariable logistic regression model that used the variables peak knee-abduction angle, center-of-mass height, and hip rotational moment excursion predicted KAM associated with PFP risk (>15.4 NM of KAM) with 92% sensitivity and 74% specificity and a C statistic of 0.93. The multivariate linear regression model that included the same predictors accounted for 70% of the variance in KAM. We identified clinical correlates to laboratory measures that combined to predict high KAM with 92% sensitivity and 47% specificity. The clinical prediction algorithm, including knee-valgus motion (odds ratio [OR] = 1.46, 95% confidence interval [CI] = 1.31, 1.63), center-of-mass height (OR = 1.21, 95% CI = 1.15, 1.26), and hamstrings strength/body fat percentage (OR = 1.80, 95% CI = 1.02, 3.16) predicted high KAM with a C statistic of 0.80., Conclusions: Clinical correlates to laboratory-measured biomechanics associated with an increased risk of PFP yielded a highly sensitive model to predict increased KAM status. This screening algorithm consisting of a standard camcorder, physician scale for mass, and handheld dynamometer may be used to identify athletes at increased risk of PFP.

Quadriceps muscle strains frequently occur in sports that require repetitive kicking and sprinting, and are common in football in its different forms around the world. This paper is a review of aetiology, mechanism of injury and the natural history of rectus femoris injury. Investigating the mechanism and risk factors for rectus femoris muscle injury aims to allow the development of a framework for future initiatives to prevent quadriceps injury in football players.

Objective: Knee abduction moment (KAM) during landing predicts non-contact anterior cruciate ligament (ACL) injury risk with high sensitivity and specificity in female athletes. The purpose of this study was to employ sensitive laboratory (lab-based) tools to determine predictive mechanisms that underlie increased KAM during landing., Methods: Female basketball and soccer players (N=744) from a single county public school district were recruited to participate in testing of anthropometrics, maturation, laxity/flexibility, strength and landing biomechanics. Linear regression was used to model KAM, and logistic regression was used to examine high (>25.25 Nm of KAM) versus low KAM as surrogate for ACL injury risk., Results: The most parsimonious model included independent predictors (β±1 SE) (1) peak knee abduction angle (1.78±0.05; p<0.001), (2) peak knee extensor moment (0.17±0.01; p<0.001), (3) knee flexion range of motion (0.15±0.03; p<0.01), (4) body mass index (BMI) Z-score (-1.67±0.36; p<0.001) and (5) tibia length (-0.50±0.14; p<0.001) and accounted for 78% of the variance in KAM during landing. The logistic regression model that employed these same variables predicted high KAM status with 85% sensitivity and 93% specificity and a C-statistic of 0.96., Conclusions: Increased knee abduction angle, quadriceps recruitment, tibia length and BMI with decreased knee flexion account for 80% of the measured variance in KAM during a drop vertical jump., Clinical Relevance: Females who demonstrate increased KAM are more responsive and more likely to benefit from neuromuscular training. These findings should significantly enhance the identification of those at increased risk and facilitate neuromuscular training targeted to this important risk factor (high KAM) for ACL injury.

Background: Prospective measures of high knee abduction moment during landing identify female athletes at high risk for non-contact anterior cruciate ligament injury. Biomechanical laboratory measurements predict high knee abduction moment landing mechanics with high sensitivity (85%) and specificity (93%). The purpose of this study was to identify correlates to laboratory-based predictors of high knee abduction moment for use in a clinic-based anterior cruciate ligament injury risk prediction algorithm. The hypothesis was that clinically obtainable correlates derived from the highly predictive laboratory-based models would demonstrate high accuracy to determine high knee abduction moment status., Methods: Female basketball and soccer players (N=744) were tested for anthropometrics, strength and landing biomechanics. Pearson correlation was used to identify clinically feasible correlates and logistic regression to obtain optimal models for high knee abduction moment prediction., Findings: Clinical correlates to laboratory-based measures were identified and predicted high knee abduction moment status with 73% sensitivity and 70% specificity. The clinic-based prediction algorithm, including (Odds Ratio: 95% confidence interval) knee valgus motion (1.43:1.30-1.59 cm), knee flexion range of motion (0.98:0.96-1.01 degrees ), body mass (1.04:1.02-1.06 kg), tibia length (1.38:1.25-1.52 cm) and quadriceps to hamstring ratio (1.70:1.06-2.70) predicted high knee abduction moment status with C statistic 0.81., Interpretation: The combined correlates of increased knee valgus motion, knee flexion range of motion, body mass, tibia length and quadriceps to hamstrings ratio predict high knee abduction moment status in female athletes with high sensitivity and specificity., Clinical Relevance: Utilization of clinically obtainable correlates with the prediction algorithm facilitates high non-contact anterior cruciate ligament injury risk athletes' entry into appropriate interventions with the greatest potential to prevent injury., (Copyright (c) 2010 Elsevier Ltd. All rights reserved.)

The purposes of this study were to compare lower-extremity kinematics during a 45 degrees and 90 degrees cutting maneuver and to examine the relationships between lower-extremity rotations during these maneuvers. The hypotheses tested were that greater internal hip and knee rotation angles would be observed during the cutting maneuver at a 90 degrees angle (90 degrees cut) compared with the maneuver performed at a 45 degrees angle (45 degrees cut) and that the increased internal hip and knee rotation would be related to increased knee abduction measures. Nineteen athletes from women's soccer teams (17.6 +/- 2.1 yr, 165.6 +/- 8.2 cm, 60.2 +/- 5.6 kg) were instructed to jump across a line and cut at the appropriate angle (either 45 degrees or 90 degrees side-step cut) and in the appropriate direction. Lower-extremity kinematic measures were taken at peak force during the stance phase. Hip internal rotation and knee internal rotation (p = 0.008) were increased during the 90 degrees cut compared with the 45 degrees cut. Mean hip flexion (p < 0.001) was also greater in the 90 degrees cut. The only significant predictor of knee abduction during both tasks was hip adduction (R = 0.49). The findings indicate that the mechanisms underlying increased knee abduction measures in athletic women during cutting tasks were primarily coronal plane motions at the hip. Trunk and hip focused strength neuromuscular training may improve the ability of athletic women to increase control of lower-extremity alignment. Therefore, these women may decrease dangerous knee loads that result from increased hip adduction during dynamic tasks, thus decreasing anterior cruciate ligament injury risk.

Soccer is the most commonly played sport in the world, with an estimated 265 million active soccer players participating in the game as on 2006. Inherent to this sport is the higher risk of injury to the anterior cruciate ligament (ACL) relative to other sports. ACL injury causes a significant loss of time from competition in soccer, which has served as the strong impetus to conduct research that focuses to determine the risk factors for injury, and more importantly, to identify and teach techniques to reduce this injury in the sport. This research emphasis has afforded a rapid influx of literature aimed to report the effects of neuromuscular training on the risk factors and the incidence of non-contact ACL injury in high-risk soccer populations. The purpose of the current review is to sequence the most recent literature relating the effects of prevention programs that were developed to alter risk factors associated with non-contact ACL injuries and to reduce the rate of non-contact ACL injuries in soccer players. To date there is no standardized intervention program established for soccer to prevent non-contact ACL injuries. Multi-component programs show better results than single-component preventive programs to reduce the risk and incidence of non-contact ACL injuries in soccer players. Lower extremity plyometrics, dynamic balance and strength, stretching, body awareness and decision-making, and targeted core and trunk control appear to be successful training components to reduce non-contact ACL injury risk factors (decrease landing forces, decrease varus/valgus moments, and increase effective muscle activation) and prevent non-contact ACL injuries in soccer players, especially in female athletes. Pre-season injury prevention combined with an in-season maintenance program may be advocated to prevent injury. Compliance may in fact be the limiting factor to the overall success of ACL injury interventions targeted to soccer players regardless of gender. Thus, interventional research must also consider techniques to improve compliance especially at the elite levels which will likely influence trickle down effects to sub-elite levels. Future research is also needed for male soccer athletes to help determine the most effective intervention to reduce the non-contact ACL injury risk factors and to prevent non-contact ACL injuries.

Soccer is the most commonly played sport in the world, with an estimated 265 million active soccer players by 2006. Inherent to this sport is the higher risk of injury to the anterior cruciate ligament (ACL) relative to other sports. ACL injury causes the most time lost from competition in soccer which has influenced a strong research focus to determine the risk factors for injury. This research emphasis has afforded a rapid influx of literature defining potential modifiable and non-modifiable risk factors that increase the risk of injury. The purpose of the current review is to sequence the most recent literature that reports potential mechanisms and risk factors for non-contact ACL injury in soccer players. Most ACL tears in soccer players are non-contact in nature. Common playing situations precluding a non-contact ACL injury include: change of direction or cutting maneuvers combined with deceleration, landing from a jump in or near full extension, and pivoting with knee near full extension and a planted foot. The most common non-contact ACL injury mechanism include a deceleration task with high knee internal extension torque (with or without perturbation) combined with dynamic valgus rotation with the body weight shifted over the injured leg and the plantar surface of the foot fixed flat on the playing surface. Potential extrinsic non-contact ACL injury risk factors include: dry weather and surface, and artificial surface instead of natural grass. Commonly purported intrinsic risk factors include: generalized and specific knee joint laxity, small and narrow intercondylar notch width (ratio of notch width to the diameter and cross sectional area of the ACL), pre-ovulatory phase of menstrual cycle in females not using oral contraceptives, decreased relative (to quadriceps) hamstring strength and recruitment, muscular fatigue by altering neuromuscular control, decreased "core" strength and proprioception, low trunk, hip, and knee flexion angles, and high dorsiflexion of the ankle when performing sport tasks, lateral trunk displacement and hip adduction combined with increased knee abduction moments (dynamic knee valgus), and increased hip internal rotation and tibial external rotation with or without foot pronation. The identified mechanisms and risk factors for non-contact ACL injuries have been mainly studied in female soccer players; thus, further research in male players is warranted. Non-contact ACL injuries in soccer players likely has a multi-factorial etiology. The identification of those athletes at increased risk may be a salient first step before designing and implementing specific pre-season and in-season training programs aimed to modify the identified risk factors and to decrease ACL injury rates. Current evidence indicates that this crucial step to prevent ACL injury is the only option to effectively prevent the sequelae of osteoarthritis associated with this traumatic injury.

Context: The relationship between generalized joint laxity and plantar pressure distribution of the foot and the potential implications for lower extremity injury have not been studied., Objective: To determine the relationship between generalized joint laxity and dynamic plantar pressure distribution. We hypothesized that individuals with greater generalized joint laxity, or hypermobility, would have greater dynamic medial midfoot pressure and loading during walking than nonhypermobile individuals., Design: Case control., Setting: Institutional biomechanics laboratory., Patients or Other Participants: Participants included 112 female soccer players between 11 and 21 years of age., Main Outcome Measure(s): Each participant was tested for generalized joint laxity using the Beighton and Horan Joint Mobility Index (BHJMI; range, 0-9) and was categorized as having either high (BHJMI score >or=4) or low (BHJMI score <4) generalized joint laxity. Peak pressure and maximum force were calculated from a dynamic, barefoot plantar pressure distribution system., Results: Peak pressure and maximum force were greater in the 27 participants categorized as having high generalized joint laxity than in the 85 participants categorized as having low generalized joint laxity. The midfoot region exhibited greater loading in participants with high generalized joint laxity than in the other participants. We found an effect of BHJMI classification in the medial midfoot; peak pressure in the dominant (F(1,109) = 11.262, P = .001) and nondominant (F(1,109) = 14.32, P < .001) sides and maximum force in the dominant (F(1,109) = 7.88, P = .006) and nondominant (F(1,109) = 9.18, P = .003) sides were greater in the high generalized joint laxity group than in the low generalized joint laxity group., Conclusions: Athletes classified as having high generalized joint laxity demonstrated increased midfoot loading. Delineation of risk factors for medial collapse of the foot, which include hypermobility in athletes, may help clinicians evaluate and prevent lower extremity injury with treatments, such as orthoses.

Context: The recent increase in women's varsity soccer participation has been accompanied by a lower extremity injury rate that is 2 to 6 times that of their male counterparts., Objective: To define the differences between lower extremity biomechanics (knee abduction and knee flexion measures) and performance (maximal vertical jump height) between National Collegiate Athletic Association Division I and III female soccer athletes during a drop vertical jump., Design: Mixed 2 x 2 design., Setting: Research laboratory., Patients or Other Participants: Thirty-four female collegiate soccer players (Division I: n = 19; Division III: n = 15) participated in the study. The groups were similar in height and mass., Intervention(s): Each subject performed a maximal vertical jump, followed by 3 drop vertical jumps., Main Outcome Measure(s): Kinematics (knee abduction and flexion angles) and kinetics (knee abduction and flexion moments) were measured with a motion analysis system and 2 force platforms during the drop vertical jumps., Results: Knee abduction angular range of motion and knee abduction external moments were not different between groups (P > .05). However, Division I athletes demonstrated decreased knee flexion range of motion (P = .038) and greater peak external knee flexion moment (P = .009) compared with Division III athletes. Division I athletes demonstrated increased vertical jump height compared with Division III (P = .008)., Conclusions: Division I athletes demonstrated different sagittal-plane mechanics than Division III athletes, which may facilitate improved performance. The similarities in anterior cruciate ligament injury risk factors (knee abduction torques and angles) may correlate with the consistent incidence of anterior cruciate ligament injury across divisions.

There is currently no consensus with regard to the most effective method to train for improved acceleration, or with regard to which kinematic variable provides the greatest opportunity for improvement in this important performance characteristic. The purpose of this study was to determine the effects of resistive ground-based speed training and incline treadmill speed training on speed-related kinematic measures and sprint start speed. The hypothesis tested was that incline treadmill training would improve sprint start time, while the ground-based resistive training would not. Corollary hypotheses were that treadmill training would increase stride frequency and ground-based training would not affect kinematics during the sprint start. Thirty-one high school female soccer players (15.7 +/- 0.5 years) were assigned to either treadmill (n = 17) or ground-based (n = 14) training groups and trained 2 times a week for 6 weeks. The treadmill group utilized incline speed training on a treadmill, while the ground-based group utilized partner band resistance ground-based techniques. Three-dimensional motion analysis was used (4.5 m mark) before and after training to quantify kinematics during the fastest of 3 recorded sprint starts (9.1 m). Both groups decreased average sprint start time from 1.75 +/- 0.12 to 1.68 +/- 0.08 seconds (p < 0.001). Training increased stride frequency (p = 0.030) but not stride length. After training, total vertical pelvic displacement and stride length predicted 62% of the variance in sprint start time for the resistive ground-based group, while stride length and stride frequency accounted for 67% prediction of the variance in sprint start time for the treadmill group. The results of this study indicate that both incline treadmill and resistive ground-based training are effective at improving sprint start speed, although they potentially do so through differing mechanisms.

Background: Despite recent evidence supporting the use of neuromuscular training to reduce anterior cruciate ligament injury risk, female athletes continue to show an increased anterior cruciate ligament injury rate in collegiate basketball and soccer when compared to males. The purpose of the current study was to identify gender and task differences in measures that may increase the risk of anterior cruciate ligament injury in female basketball and soccer athletes., Methods: Eleven female and 11 male collegiate basketball and soccer athletes were height (female mean 176 (SD 8 cm), male mean 176 (SD 8 cm)) and weight (female mean 73 (SD 7 kg), male mean 74 (SD 6 kg)) matched. Three-dimensional motion analysis was used to calculate differences in total coronal plane angular joint excursion (maximum-minimum) between male and female athletes when performing a series of medially and laterally directed drop landings., Findings: Female athletes demonstrated increased total coronal plane excursion for the hip, knee and ankle (P < 0.05) during the medial drop landing. During the lateral drop landing females displayed increased excursion at the hip and knee. When comparing tasks, the lateral drop landing resulted in greater coronal plane excursion at the hip (P < 0.05) while the knee showed no differences between movements. In contrast, females demonstrated increased ankle excursion during the medial drop task (P < 0.05)., Interpretation: Female athletes demonstrate increased lower extremity coronal plane excursion when performing single leg drop landing in both the medial and lateral direction when compared to height/weight matched male athletes. This increased coronal plane oscillation of lower extremity joints may be related to the increased risk of anterior cruciate ligament injury for female basketball and soccer athletes.

Background: Female athletes participating in high-risk sports suffer anterior cruciate ligament injury at a 4- to 6-fold greater rate than do male athletes., Hypothesis: Prescreened female athletes with subsequent anterior cruciate ligament injury will demonstrate decreased neuromuscular control and increased valgus joint loading, predicting anterior cruciate ligament injury risk., Study Design: Cohort study; Level of evidence, 2., Methods: There were 205 female athletes in the high-risk sports of soccer, basketball, and volleyball prospectively measured for neuromuscular control using 3-dimensional kinematics (joint angles) and joint loads using kinetics (joint moments) during a jump-landing task. Analysis of variance as well as linear and logistic regression were used to isolate predictors of risk in athletes who subsequently ruptured the anterior cruciate ligament., Results: Nine athletes had a confirmed anterior cruciate ligament rupture; these 9 had significantly different knee posture and loading compared to the 196 who did not have anterior cruciate ligament rupture. Knee abduction angle (P<.05) at landing was 8 degrees greater in anterior cruciate ligament-injured than in uninjured athletes. Anterior cruciate ligament-injured athletes had a 2.5 times greater knee abduction moment (P<.001) and 20% higher ground reaction force (P<.05), whereas stance time was 16% shorter; hence, increased motion, force, and moments occurred more quickly. Knee abduction moment predicted anterior cruciate ligament injury status with 73% specificity and 78% sensitivity; dynamic valgus measures showed a predictive r2 of 0.88., Conclusion: Knee motion and knee loading during a landing task are predictors of anterior cruciate ligament injury risk in female athletes., Clinical Relevance: Female athletes with increased dynamic valgus and high abduction loads are at increased risk of anterior cruciate ligament injury. The methods developed may be used to monitor neuromuscular control of the knee joint and may help develop simpler measures of neuromuscular control that can be used to direct female athletes to more effective, targeted interventions.

Background: Young athletes who specialize early in a single sport may subsequently be at increased risk of injury. While heightened injury risk has been theorized to be related to volume or length of exposure to a single sport, the development of unhealthy, homogenous movement patterns, and rigid neuromuscular control strategies may also be indicted. Unfortunately, traditional laboratory assessments have limited capability to expose such deficits due to the simplistic and constrained nature of laboratory measurement techniques and analyses. Methods: To overcome limitations of prior studies, the authors proposed a soccer-specific virtual reality header assessment to characterize the generalized movement regularity of 44 young female athletes relative to their degree of sport specialization (high vs low). Participants also completed a traditional drop vertical jump assessment. Results: During the virtual reality header assessment, significant differences in center of gravity sample entropy (a measure of movement regularity) were present between specialized (center of gravity sample entropy: mean = 0.08, SD = 0.02) and nonspecialized center of gravity sample entropy: mean = 0.10, SD = 0.03) groups. Specifically, specialized athletes exhibited more regular movement patterns during the soccer header than the nonspecialized athletes. However, no significant between-group differences were observed when comparing participants' center of gravity time series data from the drop vertical jump assessment. Conclusions: This pattern of altered movement strategy indicates that realistic, sport-specific virtual reality assessments may be uniquely beneficial in exposing overly rigid movement patterns of individuals who engage in repeated sport specialized practice. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Visual biofeedback has been shown to facilitate injury-resistant movement acquisition in adolescent athletes. Visual biofeedback is typically thought to foster implicit learning by stimulating athletes to focus attention externally (on movement outcome). However, biofeedback may also induce explicit learning if the athlete uses the visual information to consciously guide movement execution (via an internal focus). To determine the degree to which athletes reported statements indicating implicit or explicit motor learning after engaging in a visual biofeedback intervention. Prospective cohort study. Three-dimensional motion-analysis laboratory. Twenty-five adolescent female soccer athletes (age = 15.0 ± 1.5 years, height = 165.7 ± 5.9 cm, mass = 59.4 ± 10.6 kg). Standard 6-week neuromuscular training intervention (three 90-minute sessions/wk), with added visual biofeedback sessions (2 sessions/wk). For the biofeedback training, participants performed squatting and jumping movements while interacting with a visual rectangular stimulus that mapped key parameters associated with injury risk. After the last biofeedback session in each week, participants answered open-ended questions to probe learning strategies. Responses to the open-ended questions were categorized as externally focused (ie, on movement outcome, suggestive of implicit learning), internally focused (ie, on movement itself, suggestive of explicit learning), mixed focus, or other. A total of 171 open-ended responses were collected. Most of the responses that could be categorized (39.2%) were externally focused (41.8%), followed by mixed (38.8%) and internally focused (19.4%). The frequency of externally focused statements increased from week 1 (18%) to week 6 (50%). Although most statements were externally focused (suggesting implicit learning), the relatively large proportion of internal- and mixed-focus statements suggested that many athletes also engaged in explicit motor learning, especially in early practice sessions. Therefore, biofeedback may affect motor learning through a mixture of implicit and explicit learning. [ABSTRACT FROM AUTHOR]

Context: As high school female athletes demonstrate a rate of noncontact anterior cruciate ligament (ACL) injury 3-6 times higher than their male counterparts, research suggests that sagittal-plane hip strength plays a role in factors associated with ACL injuries. Objective: To determine if gender or age affect hip-abductor strength in a functional standing position in young female and male athletes. Design: Prospective cohort design. Setting: Biomechanical laboratory. Participants: Over a 3-y time period, 852 isokinetic hip-abduction evaluations were conducted on 351 (272 female, 79 male) adolescent soccer and basketball players. Intervention: Before testing, athletes were secured in a standing position, facing the dynamometer head, with a strap secured from the uninvolved side and extending around the waist just above the iliac crest. The dynamometer head was positioned in line with the body in the coronal plane by aligning the axis of rotation of the dynamometer with the center of hip rotation. Subjects performed 5 maximum-effort repetitions at a speed of 120°/s. The peak torque was recorded and normalized to body mass. All test trials were conducted by a single tester to limit potential interrater test error. Main Outcome Measure: Standing isokinetic hip-abduction torque. Results: Hip-abduction torque increased in both males and females with age (P < .001) on both the dominant and nondominant sides. A significant interaction of gender and age was observed (P < .001), which indicated that males experienced greater increases in peak torque relative to body weight than did females as they matured. Conclusions: Males exhibit a significant increase in normative hip-abduction strength, while females do not. Future study may determine if the absence of similar increased relative hip-abduction strength in adolescent females, as they age, may be related to their increased risk of ACL injury compared with males. [ABSTRACT FROM AUTHOR]

Background: Longitudinal changes in white matter (WM) integrity have been reported following cumulative exposure to sub‐concussive head impacts (SCI) incurred during sports. SCI exposure is typically quantified using accelerometers that use an arbitrary g‐force threshold for impact detection; however, this approach does not differentiate true impacts from non‐physiological events, such as high‐frequency cutaneous vibrations. This leads to a high false positive rate and the tendency to overestimate SCI exposure. Hypothesis/Purpose: To examine whether machine learning classification trained on video‐verified impacts can produce more accurate quantification of SCI exposure and whether this can reveal associations between cumulative exposure and diffusion tensor imaging (DTI)‐measured longitudinal WM changes in athletes. Methods: Pre‐ and post‐season brain MRI scans were collected from 46 female high school soccer athletes. Athletes’ SCI exposure was recorded during their competitive season using head‐mounted accelerometers. 24 athletes were assigned to a “Treatment Group” (TG) and were also video recorded during 17 of their games, while the remaining 22 athletes were assigned to a “Control Group” (CG) and were unrecorded. The TG video was used to verify whether the sensor‐recorded impacts during those games were true head impacts or false positives. This dataset, along with the corresponding true/false labels, was used to train a machine learning classifier to learn a mapping between the accelerometer data and their respective labels. The trained model was then used to classify and filter the impacts recorded for the CG athletes by removing their predicted false positives. The CG athletes’ SCI exposure in both the unfiltered and filtered conditions was correlated with their pre‐ to post‐season changes in DTI measures of mean diffusivity (MD), axial diffusivity (AD), radial diffusivity (RD), and fractional anisotropy (FA). Results: During the TG athletes’ 17 video‐recorded games, 5146 impacts were recorded and 1128 were confirmed as true positives (22.0% accuracy). After training the machine learning classifier, the model was able to achieve 83.5% accuracy on this dataset. Associating the CG athletes’ unfiltered SCI exposure to pre‐ to post‐season WM changes revealed no significant associations based on voxel‐wise analysis over the whole brain WM network; however, after removing predicted false positives, the filtered SCI exposure revealed significant associations with changes in MD, RD, and FA (all p < 0.05). Conclusion: Machine learning classification of sensor‐recorded SCI exposure exhibits superior accuracy and sensitivity to threshold‐based detection used in standard accelerometry. Accurate quantification of SCI exposure also reveals associations with longitudinal WM changes. [ABSTRACT FROM AUTHOR]

The article presents information on a study which analyzes the effects of the Nordic hamstring strengthening exercise on the biceps femoris long head (BFIh), biceps femoris short head (BFsh), semitendinosus (SMT), and semi- membranosus (SMM) muscles. The study used magnetic resonance imaging (MRI) to analyze the site-specific activation of this exercise on different muscles of the thigh and muscle damage. The methods and results of the study are also discussed.