Female Youth Soccer Research Articles

Age and Knee Confidence Effects on LESS and LESS-RMC Scores in Female Youth Soccer Players

INTRODUCTION: Anterior Crucial Ligament (ACL) injuries are common in female soccer players and can have serious, even lifelong consequences. The Landing Error Scoring System (LESS) and a modification of the LESS, the LESS-RMC, have been useful tools in screening athletes and identifying individuals at “high-risk” so appropriate interventions could be provided. However, it is unclear how knee confidence and age influences these screening tools in female soccer athletes. PURPOSE: The aim of this study was to investigate the effects of age and knee confidence on ACL injury risk classification in female youth soccer players. METHODS: 178 healthy female youth soccer players (ht: 1.63±0.07m, mass: 48.8±4.9kg, age: 14.1±1.5yrs) participated in this study. Participants were asked to jump from a 30cm box a distance 50% of their height where they immediately performed a maximum vertical jump and landing upon initial ground contact. Two HD cameras were used to record (60 Hz) this motion in the frontal and sagittal planes. The video of the task was then used to assess the participant’s ACL injury risk by evaluating these landings using the LESS and LESS-RMC procedures. Knee confidence was evaluated by using a 5-point Likert scale in response to an item asking “How much do you trust your knee” from the knee-related quality of life subscale in the KOOS knee questionnaire. The participants were classified as confident if they answered “completely” and not confident for all other responses. Two-way ANOVAs were used to investigate the effects of age group (11-12, 13-14, 15-16 and 17-18 y) and knee confidence on the LESS and LESS-RMC scores. RESULTS: There was a statistically significant main effect of age on the LESS score, [F (3, 167) = 2.667, p = 0.049.]. Post-hoc tests revealed that the age group of 11-12 years displayed significantly higher LESS scores (6.43±2.14) than the 17-18 group (4.49±2.11) (p = 0.029). There was no significant main effect for knee confidence (p = 0.501). CONCLUSION: The results reveal that female soccer players in the 11-12 age range are at a greater risk of ACL injury than the 17-18 age range. Further research should be conducted to examine the mechanical contribution to this risk and methods to reduce injury risk across age ranges.

Characterizing head impact exposure in youth female soccer with a custom-instrumented mouthpiece

ABSTRACTWhile many research efforts have focused on head impact exposure in professional soccer, there have been few studies characterizing exposure at the youth level. The aim of this study is to evaluate a new instrumentation approach and collect some of the first head impact exposure data for youth female soccer players. Athletes were instrumented with custom-fit mouthpieces that measure head impacts. Detailed video analysis was conducted to identify characteristics describing impact source (e.g., kick, header, throw). A total of 763 verified head impacts were collected over 23 practices and 8 games from 7 athletes. The median peak linear accelerations, rotational velocities, and rotational accelerations of all impacts were 9.4 g, 4.1 rad/s, and 689 rad/s2, respectively. Pairwise comparisons resulted in statistically significant differences in kinematics by impact source. Headers following a kicked ball had the highest accelerations and velocity when compared to headers from thrown or another header.

CHRONIC LACK OF SLEEP IS ASSOCIATED WITH INCREASED SPORTS INJURY IN ADOLESCENTS: A SYSTEMATIC REVIEW AND META-ANALYSIS

Background:Although sleep has been identified as an important modifiable risk factor for sports injury, the effect of decreased sleep on sports injuries in adolescents is poorly studied.Purpose:To ...

Postural Control Deficits After Repetitive Soccer Heading.

To determine the acute effects of repetitive soccer heading on postural control. Prospective study; participants were divided into 2 groups: a soccer heading group and a control group. Biomechanics laboratory. One hundred sixty participants, including youth (age = 13.0 ± 0.8 years), high school (age = 17.2 ± 1.0 years), and collegiate (age = 20.2 ± 1.3 years) male and female soccer players, participated in this study. Participants in the soccer heading group performed 12 soccer headers (initial velocity = 11.2 m/s). Postural control testing was performed both before (PRE) and immediately after (POST) the purposeful soccer headers. Control participants performed postural control testing PRE and POST a 15-minute wait period. During postural control testing, participants were asked to stand on the MobileMat (Tekscan Inc, Boston, Massachusetts) for two 2-minute intervals with their hands on their hips and their feet together with one eyes-open and one eyes-closed trial. Using the center-of-pressure data, 95% area, sway velocity, and ApEn were calculated. Multilevel linear models were used to analyze the effects of age, sex, group, condition, and concussion history simultaneously. Participants in the soccer heading group had significantly higher sway velocity POST than participants in the control group after controlling for age, sex, concussion history, condition, and PRE (t = -3.002; P = 0.003; 95% confidence interval, -0.482 to -0.100). There were no significant differences from PRE to POST for 95% area, M/L ApEn, and A/P ApEn. Repetitive soccer heading does not affect most postural control measures, even among youth athletes. However, sway velocity increased after heading relative to control participants independent of age, sex, and concussion history.

A Nationwide Follow-up Survey on the Effectiveness of an Implemented Neuromuscular Training Program to Reduce Acute Knee Injuries in Soccer Players

Background:A cruciate ligament (CL) injury is a severe injury in soccer. Neuromuscular training programs have a well-documented preventive effect, but there are few studies on the effectiveness of such a program at a national level. The Swedish Knee Control Program (KCP) was found to be effective in preventing CL injuries in youth female soccer players. The KCP was implemented nationwide in Sweden in 2010.Purpose:To evaluate the effectiveness of the Swedish KCP in reducing acute knee injuries in soccer players at a nationwide level.Study Design:Descriptive epidemiology study.Methods:All licensed soccer players in Sweden are covered by the same insurance company. Using this insurance database, around 17,500 acute knee injuries that were reported to the insurance company between 2006 and 2015 were included in the study. By matching the number of licensed soccer players with the number of reported injuries each year, the annual incidence of knee and CL injuries was able to be calculated. To evaluate the spread of the KCP nationally, a questionnaire was sent to all 24 Swedish district football associations (FAs) with questions regarding KCP education. The number of downloads of the KCP mobile application (app) was obtained.Results:The incidence of CL injuries decreased during the study period for both male (from 2.9 to 2.4 per 1000 player-years) and female players (from 4.9 to 3.9 per 1000 player-years). The overall incidence of knee injuries decreased in both male (from 5.6 to 4.6 per 1000 player-years) and female players (from 8.7 to 6.4 per 1000 player-years). Comparing before and after the nationwide implementation of the KCP, there was a decrease in the incidence of CL injuries by 6% (rate ratio [RR], 0.94 [95% CI, 0.89-0.98]) in male players and 13% (RR, 0.87 [95% CI, 0.81-0.92]) in female players and a decrease in the incidence of knee injuries by 8% (RR, 0.92 [95% CI, 0.89-0.96]) and 21% (RR, 0.79 [95% CI, 0.75-0.83]), respectively (P < .01 for all). This trend corresponded to a reduction of approximately 100 CL injuries each year in Sweden. A total of 21 of 24 district FAs held organized KCP educational courses during the study period. The percentage of district FAs holding KCP courses was between 46% and 79% each year. There were 101,236 downloads of the KCP app.Conclusion:The KCP can be considered partially implemented nationwide, and the incidence of knee and CL injuries has decreased in both sexes at a nationwide level.

Lower limb injury prevention programs in youth soccer: a survey of coach knowledge, usage, and barriers

BackgroundParticipation in youth soccer carries a significant risk of injury, most commonly non-contact injuries of the lower extremity. A growing body of research supports the use of neuromuscular interventions by teams to prevent such injuries, yet the uptake of these recommendations by soccer teams remains largely unexplored. The purposes of the study were to determine (1) the level of awareness by youth coaches of injury prevention programs and their efficacy; (2) the number of youth coaches that use these interventions; and (3) barriers and potential facilitators to implementing a sustainable injury prevention program.MethodsFour hundred eighteen coaches of male and female youth soccer teams were emailed an online blinded survey. This survey consisted of 26 questions covering coaches’ demographics, level of training, experience with injuries among players, and use of injury prevention programs. Question development was guided by the RE-AIM Sports Setting Matrix in combination with findings from the literature review and expert experience from orthopaedic surgeons specializing in sport medicine.ResultsOf the 418 coaches contacted, 101 responded. Only 29.8% of respondents used an injury prevention program in the prior soccer season. Coaches that had completed one or more coaching courses were more likely to use an intervention. Of those that did not already use an intervention, coaches agreed or strongly agreed that they would consider using one if it could be used in place of the warm up and take no more than 20 min (74.0%), if they could access information about the exercises (84.0%), and if the exercises could be properly demonstrated (84.0%). Additionally, 84% of coaches that did not already use an intervention agreed or strongly agreed that knowing that interventions may reduce a player’s risk of injury by 45% would affect whether they would use one.ConclusionThis study suggests that the current use and awareness of injury prevention programs is limited by a lack of communication and education between sporting associations and coaches, as well as perceived time constraints. The results also suggest that improving coaching education of injury prevention could increase the frequency of intervention use.

Relative Age Effect Among Elite Youth Female Soccer Players across the United States

Relative Age Effect Among Elite Youth Female Soccer Players across the United States

Efficacy of Injury Prevention Training Is Greater for High-Risk vs Low-Risk Elite Female Youth Soccer Players

Background: The efficacy of robustness training for high- versus low-risk individuals within high-risk groups is currently unknown. Purpose: To explore the efficacy of robustness training on injury risk factors among female youth soccer players and to examine if high-risk athletes are greater responders to such training. Study Design: Controlled laboratory study. Methods: A total of 125 elite youth female soccer players on the English FA talent pathway were randomly selected into a training group (n = 71) or a control group (n = 54). Relative leg stiffness, 2-dimensional knee valgus and knee flexion range of motion from a single-legged countermovement jump, and probability of high knee abduction moment (pKAM) risk were all determined before and after a 16-week robustness training program. For further analysis, participants in the training group were split into groups based on risk: high risk (pKAM >0.80, n = 33) and low risk (pKAM <0.55, n = 33). Magnitude-based inferences were used to explore differences between the control and intervention groups and the high- and low-risk groups. Results: Magnitude-based inferences demonstrated significant beneficial effects in the training group for knee valgus, pKAM, and leg stiffness as compared with the control group. The control group demonstrated possible worthwhile differences in knee flexion range of motion as compared with the intervention group. The high-risk group demonstrated likely/very likely worthwhile differences versus the low-risk group for all parameters. Conclusion/Clinical Relevance: Robustness training induces significant beneficial improvements in injury risk factors among female youth soccer players. The beneficial effects of this multidimensional program are greater for those classified as high risk.

Physical Characteristics of Elite Youth Female Soccer Players Characterized by Maturity Status.

Emmonds, S, Scantlebury, S, Murray, E, Turner, L, Robsinon, C, and Jones, B. Physical characteristics of elite youth female soccer players characterized by maturity status. J Strength Cond Res 34(8): 2321-2328, 2020-The purpose of this study was to investigate the influence of maturity status on the physical characteristics of youth female soccer players. One hundred fifty-seven players from 3 elite soccer academies in England completed assessments of anthropometry, strength (isometric midthigh pull), lower-body power (countermovement jump [CMJ]), aerobic capacity (Yo-Yo intermittent recovery test level 1), change of direction (CoD: 505-left/right), and speed (10 and 30 m). Each player was classified into 1 of 6 maturity groups based on their estimated years from peak height velocity (YPHV). Magnitude-based inferences were used to assess for the practical significance between consecutive groups. Speed, CoD time, CMJ, and aerobic capacity were all possibly most likely better in more mature players. However, there was a likely difference in relative peak force between maturity groups -0.5 YPHV (27.13 ± 4.24 N·Kg) and 0.5 YPHV (24.62 ± 3.70 N·Kg), which was associated with a likely difference in 10-m sprint time (-0.5 YPHV: 2.00 ± 0.12 vs. 0.5 YPHV 2.08 ± 0.16 seconds) and unclear changes in CMJ and CoD time. Findings provide novel comparative data for this cohort relative to maturity status and can be used by strength and conditioning coaches to inform the design of training programs for youth female soccer players. Strength and conditioning coaches should be aware that youth female soccer players may experience a decrease in relative strength around peak height velocity, which may impact upon the speed, CoD time, and CMJ of players.

The number of purposeful headers female youth soccer players experience during games depends on player age but not player position

ABSTRACTPurpose: The aim of this study was to describe the frequency and characteristics of purposeful soccer heading in youth players based on age, position, and head impact location.Methods: Game video was recorded for three female youth teams [under-13 (U13), under-14 (U14), and under-15 (U15)] for an entire season. Purposeful headers were categorized for these three teams and their opposition.Results: The median number of headers experienced during games was one, and the minimum number of headers was zero. The maximum number of headers performed during a game by a U13 player was eight, and nine for U14 and U15 players. There were statistically significant differences in the number of headers performed in the different age groups (p < 0.05), but no significant differences between player position (p > 0.05). There was no significant association between head impact location and game scenario (p > 0.05).Conclusions: Our study shows that youth players frequently head the ball during games. This information may guide data-driven approaches regarding heading restrictions in youth soccer.

Prevention of Ankle Sprain Injuries in Youth Soccer and Basketball: Effectiveness of a Neuromuscular Training Program and Examining Risk Factors.

The primary objective of this study was to examine the effectiveness of a neuromuscular training (NMT) warm-up program in reducing the risk of ankle sprain injury (ASI) in youth soccer and basketball. The secondary objective included the evaluation of risk factors for ASI. Secondary analysis of pooled data from 5 studies. Male and female youth (11-18 years) soccer and basketball players (n = 2265) in Alberta, Canada. Ankle sprain injury was the primary outcome and was recorded using a validated prospective injury surveillance system consistent in all studies. The primary exposure of interest was NMT warm-up, which included aerobic, strength, agility, and balance components. Multivariable Poisson regression, controlling for clustering by team and offset for exposure hours, was used to estimate incidence rate ratios (IRRs) with 95% confidence intervals (CIs), with considerations for confounding and effect modification and evaluating all covariates as potential risk factors. A total of 188 ASIs were reported in 171 players. Neuromuscular training significantly reduced the risk of ASI [IRR = 0.68 (95% CI; 0.46-0.99)]. Independent risk factors for ASI included previous ASI [IRR = 1.98 (95% CI; 1.38-2.81)] and participation in basketball versus soccer [IRR = 1.83 (95% CI; 1.18-2.85)]. Sex, age, body mass index, and previous lower extremity injury (without previous ASI) did not predict ASI (P > 0.05). Exposure to an NMT program is significantly protective for ASI in youth soccer and basketball. Risk of ASI in youth basketball is greater than soccer, and players with a history of ASI are at greater risk.

Sport Specialization Is Associated with Impaired Sleep and Well-Being in Female Adolescent Athletes

Background: Sport specialization has been found to be associated with increased injury risk in youth athletes. Sleep and well-being have also been shown to be modifiable risk factors for injury in this population, but the relationship between specialization, sleep and well-being is unknown. The purpose of this study was to evaluate the relationship between sport specialization, sleep and subjective well-being in female youth soccer players. Methods: Forty-nine female youth soccer players (ages 13-18) underwent pre-season evaluation to determine age, soccer experience, and sport participation. During a subsequent 4-month …

Risk factors associated with self-reported injury history in female youth soccer players

ABSTRACTBackground: studies that investigate risk factors for musculoskeletal injuries in female youth athletes are limited, especially related to training attributes and position status.Objective: to determine risk factors including training attributes and position status for a self-reported musculoskeletal injury history in female youth soccer players.Methods: we conducted a cross-sectional study of young female soccer players (mean age: 13.6 ± 2.3 years). we asked about their history of musculoskeletal injuries using an electronic questionnaire. the proportion of young female soccer players with and without a history of soccer-related musculoskeletal injuries were compared based on physical characteristics, training attributes, position status (single vs. multiple), lower extremity strength, and joint laxity. a binary logistic regression analysis was used to generate, and adjusted odds ratios adjusted for potential co-variates (aor). a 95% confidence interval (95%ci) that did not cross one or p < 0.05 were considered statistically significant.Results: a total of 160 young female soccer players (mean age: 13.6 ± 2.3 years) participated in the study. an independent association was found between prior musculoskeletal injuries and older ages (aor: 1.60, 95%ci: 1.17, 2.20, p = 0.004), higher weight (aor: 1.10, 95%ci: 1.01, 1.20, p = 0.026), and greater bmi (aor: 1.43, 95%ci: 1.07, 1.90, p = 0.014).Conclusions: musculoskeletal injuries were associated with age, weight, and bmi in female youth players. the current study indicates that maintaining proper body composition may be beneficial to reduce musculoskeletal injuries among female youth soccer players.

The Effects of Subconcussive Impacts on Heart Rate Variability In Female Youth Soccer Players

BackgroundANS function can be measured noninvasively and relatively inexpensively through heart rate variability (HRV). Reduced HRV is representative of an uncoupling between the ANS and cardiovascular system, which may be proportional to the severity of a neurological injury. Reduced HRV has been observed in patients diagnosed with a sport‐related concussion, and therefore may be a useful outcome measure in identifying the chronic effects of heading during a youth soccer season.ObjectivesThe purpose of this study was to evaluate the effects of one season of competitive soccer, with the inherent subconcussive header impacts, on autonomic function in female youth soccer players.ParticipantsTwenty‐three female youth soccer players (13.4 ± 0.84 years old) were recruited from three competitive soccer teams.MethodsThe number of headers performed during the season were quantified using game video analysis. Players that performed fewer than the average number of headers (20) at the end of the season were classified into the “low header” group (N=13), while players with 20 or more headers at the end of the season were classified into the “high header” group (N=10). A five‐minute resting electrocardiogram data was collected from all players at baseline and post‐season. These data were analyzed using a two‐way mixed ANOVA in order to calculate heart rate variability time‐domain and frequency‐domain measures, which included mean heart rate, standard deviation of the N‐N interval, total power, low frequency, high frequency, and low to high frequency ratio (LF/HF).ResultsThere was a statistically significant interaction between time and group for LF/HF from preseason (6.24 ± 5.77; 2.96 ± 1.81) to postseason (6.79 ± 6.75; 1.90 ± 1.02) in the low and high header groups, respectively (p=.024, partial h2=0.313). There were no other statistically significant changes in HRV for any other time or frequency domain outcome measure.ConclusionOur preliminary findings indicate that the LF/HF in the high header group differed from the low header group over the course of a soccer season. This may indicate that an increased number of chronic head impacts might result in an imbalance between sympathetic and parasympathetic activity, which would signify an alteration in autonomic function. These preliminary results demonstrate that additional research is needed in order to further understand the effects of heading on ANS function.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Inevitable Relative Age Effects in Different Stages of the Selection Process among Male and Female Youth Soccer Players

The relative age effect (RAE) in the selection of young soccer players is a well-known phenomenon. The purpose of this study was to examine the relative age effect existing despite strategies that have been implemented to avoid its presence in the selection process. We also aimed to investigate the RAE during the three different selection stages for B13, B14 (boys), and G13, G14 (girls), and gender differences in the RAE. This was achieved by collecting data from everyone who played soccer in Troendelag, and data that would illuminate the RAE during the three stages of selection for the regional teams of the 2015/2016 season. Mann–Whitney U-tests and Chi-square tests were used as statistical methods. The main finding of this study is that, despite the intention to reduce RAE in the selection process according to the criterion that at least 40% of the players should be born in the second half of the year, both the early-born boys and girls are more likely to be selected. The results also show that the RAE occurs gradually, and the longer the players are in the selection process the more prominent it is. This study highlights the importance of being aware of the RAE when selecting young players.

Vertical and Horizontal Asymmetries Are Related to Slower Sprinting and Jump Performance in Elite Youth Female Soccer Players.

Bishop, C, Read, P, McCubbine, J, and Turner, A. Vertical and horizontal asymmetries are related to slower sprinting and jump performance in elite youth female soccer players. J Strength Cond Res 35(1): 56-63, 2021-Interlimb asymmetries have been shown to be greater during vertical jumping compared with horizontal jumping. Notable interlimb differences have also been established at an early age in male youth soccer players. Furthermore, given the multiplanar nature of soccer, establishing between-limb differences from multiple jump tests is warranted. At present, a paucity of data exists regarding asymmetries in youth female soccer players and their effects on physical performance. The aims of this study were to quantify interlimb asymmetries from unilateral jump tests and examine their effects on speed and jump performance. Nineteen elite youth female soccer players performed a single-leg countermovement jump (SLCMJ), single, triple, and crossover hops for distance, and a 20-m sprint test. Test reliability was good to excellent (intraclass correlation coefficient = 0.81-0.99) and variability acceptable (coefficient of variation = 1.74-5.42%). A 1-way analysis of variance highlighted larger asymmetries from the SLCMJ compared with all other jump tests (p < 0.05). Pearson's correlations portrayed significant relationships between vertical asymmetries from the SLCMJ and slower sprint times (r = 0.49-0.59). Significant negative relationships were also found between horizontal asymmetries during the triple hop test and horizontal jump performance (r = -0.47 to -0.58) and vertical asymmetries during the SLCMJ and vertical jump performance (r = -0.47 to -0.53). The results from this study highlight that the SLCMJ seems to be the most appropriate jump test for identifying between-limb differences with values ∼12% showing negative associations with sprint times. Furthermore, larger asymmetries are associated with reduced jump performance and would appear to be direction specific. Practitioners can use this information as normative data to be mindful of when quantifying interlimb asymmetries and assessing their potential impact on physical performance in youth female soccer players.

Influence of age on the anthropometric and performance characteristics of high-level youth female soccer players

The purpose of this study was to evaluate the anthropometric and performance characteristics of high-level youth female soccer players by annual-age category (Under 10 (U10)–U16). Data were collected from 157 female soccer players (U16, n = 46; U14, n = 43; U12, n = 38; U10, n = 30), recruited from three high-level female soccer academies in England. Players completed assessments of anthropometry (height and body mass), isometric mid-thigh pull strength, jump height, aerobic capacity, change of direction (505-left/right) and speed (10 and 30 m). Magnitude based-inferences were used to assess for practical significance between consecutive age groups. Height ( very likely–most likely), body mass ( very likely–most likely), absolute strength ( most likely), jump height ( likely–very likely) and distance on the YYIRL1 ( possibly–most likely) were greater in older players. Both speed and change of direction time were most likely to very likely lower in older players. However, only most likely trivial–possibly trivial differences were observed in relative strength between age groups. Findings suggest that physical characteristics except for relative strength differentiate by age categories. These findings provide comparative data and target reference data for such populations and can be used by coaches and practitioners for player development purposes. Practitioners should be aware that relative strength does not differ between age categories in high-level youth female soccer players.

A Conditional Process Analysis of the Coach-Created Mastery Climate, Task Goal Orientation, and Competence Satisfaction in Youth Soccer: The Moderating Role of Controlling Coach Behavior

The purpose of this study was to investigate controlling coach behavior as a boundary condition for the relationship between a mastery climate, task goal orientation, and competence satisfaction in youth soccer. Latent conditional process modeling was conducted with a sample of 1,119 female and male youth soccer players 10–15 years of age. Results indicated that the interaction between controlling coach behavior and coach-created mastery climate accounted for 4% variance in task goal orientation. Furthermore, the indirect link between coach-created mastery climate and competence, through task goal orientation, was significant at all levels of controlling coach behavior, yet decreased from low (–1 SD; B =.40, 95% confidence interval [CIBC] [.28,.52]), to moderate (M; B =.35, 95% CIBC [.26,.46]), to high levels (+1 SD; B =.31, 95% CIBC [.22,.41]). Findings are interpreted as supporting the idea that controlling coach behavior abates the internalization of mastery values, thereby undermining the relationship between the coach-created mastery climate and players' competence satisfaction.

Leg Stiffness in Female Soccer Players: Intersession Reliability and the Fatiguing Effects of Soccer-Specific Exercise.

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.

Risk Factors for Lower Extremity Overuse Injuries in Female Youth Soccer Players.

Background:Youth soccer injuries are common and of increasing concern, with sport specialization occurring at younger ages. Limited research is available regarding overuse injuries and risk factors in young female athletes.Purpose:To identify the number and rate of overuse injuries in female soccer players (ages 12-15 years), describe the anatomic location and type of injury, and evaluate contributing risk factors.Study Design:Case-control study; Level of evidence, 3.Methods:A total of 351 female youth soccer players, ages 12 to 15 years, from Washington State were evaluated from 2008 to 2012. Players with lower extremity overuse injuries were identified through weekly emails and were interviewed by telephone to obtain data on injury type and body region. We evaluated the association between overuse injuries and preseason risk factors, including joint hypermobility, hip and knee muscle strength, and jump biomechanics, using Poisson regression to estimate relative risk (RR) and 95% CIs.Results:The incidence rate for first-time lower extremity overuse injuries was 1.7 per 1000 athlete-exposure hours (AEH; 95% CI, 1.4-2.2), and that for repeat injuries was 3.4 per 1000 AEH (95% CI, 2.1-5.6). Knee injuries accounted for 47% of overuse injuries. Increased valgus was associated with a 3.2-fold increased risk (95% CI, 1.52-6.71) for knee injury. A 1–standard deviation (SD) increase in hamstring strength was associated with a 35% decreased risk (RR, 0.65; 95% CI, 0.46-0.91) for overuse knee injuries, and a 1-SD increase in quadriceps strength was associated with a 30% decreased risk (RR, 0.70; 95% CI, 0.50-0.98). A 1-SD increase in hip flexor strength was associated with a 28% decreased risk (RR, 0.72; 95% CI, 0.51-1.00) for overuse knee injuries, and a 1-SD increase in external rotation strength was associated with a 35% decreased risk (RR, 0.65; 95% CI, 0.46-0.91). Playing on more than 1 soccer team was associated with a 2.5-fold increased risk (95% CI, 1.08-5.35) for overuse knee injuries, and participating in other physical activities was associated with a 61% decreased risk (odds ratio, 0.39; 95% CI, 0.15-0.81).Conclusion:In this study, lower extremity overuse injuries in female youth soccer players affected primarily the knee. Lower knee separation distance, decreased lower extremity strength, and playing on more than 1 soccer team increased injury risk.