Head Games: A Systematic Review and Meta-analysis Examining Concussion and Head Impact Incidence Rates, Modifiable Risk Factors, and Prevention Strategies in Youth Tackle Football.

OBJECTIVES: The aims were to (1) examine the rates and mechanisms of concussion and head impact in youth football (high school level or younger); (2) identify modifiable risk factors for concussion and head impact; and (3) evaluate the effectiveness of prevention strategies in tackle football at any level. METHODS: Nine databases (CINAHL Plus with Full Text; Cochrane Central Register of Controlled Trials; EMBASE; ERIC; Ovid MEDLINE(R) and Epub Ahead of Print, In-Process & Other Non-Indexed Citations and Daily; ProQuest Dissertations & Theses Global Database; PsycINFO; Scopus; and SPORTDiscus with Full Text) were searched using the search strategy focusing on four main concepts: concussion/head impact, tackle football, modifiable risk factors, and primary prevention. Two reviewers completed title, abstract, and full-text screening as well as risk of bias assessment (using the Downs and Black checklist), with a third author available to resolve any disagreements. MAIN RESULTS: After removing duplicates, 1911 articles were returned. Fifty-eight articles were included in the review and 20 in the meta-analysis. The overall combined rates of concussion (including game and practice-related concussion) based on the meta-analysis were 0.78 concussions/1000 athlete exposures [95% confidence interval (CI) 0.67-0.89] for high school football (ages 13-19) and 1.15 concussions/1000 athlete exposures (95% CI 0.89-1.41) for minor football players (ages 5-15). There is evidence that contact training and practice contact restrictions have reduced the rate of head impacts and concussion. Heads Up Football (an intervention focused on coach education and contact training) has been shown to reduce the rate of concussion by 32% and head impacts by 38% amongst high school football players. Limiting contact practices in high schools to 2 days per week reduced practice head impacts per player-season by 42%, and limiting full contact in practice to 75 min per week in the second week of the season and 60 min in week 3 and beyond resulted in a 54% decrease in the practice-related concussion rate (p = 0.003). CONCLUSIONS: This review identified a critical need for interventions to address the high rates of concussion and head impact in youth football. To date, contact training and contact restrictions have the strongest evidence supporting their effectiveness at reducing these rates. Future research should use consistent concussion definitions and validated injury surveillance systems, and ensure complete reporting of participant characteristics and sampling details. Prospero ID CRD42020193775.

CCL22 is a biomarker of cartilage injury and plays a functional role in chondrocyte apoptosis.

BACKGROUND: Osteoarthritis (OA) is one of the leading causes of disability worldwide. Previous history of knee injury is a significant risk factor for OA. It has been established that low-level chronic inflammation plays a pivotal role in the onset and pathogenesis of OA. The primary aim of this research was to determine if a history of knee joint injury is associated with systemic inflammation. A secondary aim was to determine if systemic inflammation is related to knee pain and joint structure. METHODS: Differences in serum cytokine association networks, knee joint structural changes (MRI), and self-reported pain (i.e., Knee Injury and Osteoarthritis Outcome Score Pain subscale, KOOSPAIN and Intermittent and Constant Osteoarthritis Pain score, ICOAP) between individuals who had sustained a youth (aged 15-26 years) sport-related knee injury 3-10 years previously and age- and sex-matched controls were examined. Proteins of interest were also examined in an OA rat model. RESULTS: Cytokine association networks were found to differ significantly between study groups, yet no significant associations were found between networks and KOOSPAIN or MRI-defined OA. A group of cytokines (MCP1/CCL2, CCL22 and TNFα) were differentially associated with other cytokines between study groups. In a pre-clinical rat OA model, serum CCL22 levels were associated with pain (r = 0.255, p = 0.045) and structural changes to the cartilage. CCL22 expression was also observed in human OA cartilage and furthermore, CCL22 induced apoptosis of isolated human chondrocytes. DISCUSSION: These results suggest that CCL22 may be an early factor in the onset/pathogenic process of cartilage degeneration and/or related to pain OA.

Serum cartilage oligomeric matrix protein (COMP) expression in individuals who sustained a youth sport-related intra-articular knee injury 3-10 years previously and uninjured matched controls.

OBJECTIVE: This study investigates the relationship between a youth sport-related intra-articular knee injury and cartilage oligomeric matrix protein (COMP), a biomarker of cartilage turnover. DESIGN: Participants included a sub-sample (n = 170) of the Alberta Youth Prevention of Early Osteoarthritis (PrE-OA) study group. Specifically, 85 individuals with a 3-10 year history of sport-related intra-articular knee injury and 85 age, sex and sport-matched controls. COMP levels were investigated in serum. Between group differences in COMP levels, COMP fragmentation patterns and, the relationship between serum COMP and clinical outcomes (i.e., Magnetic Resonance Imaging (MRI) Osteoarthritis Knee Score; MOAKS, Knee Osteoarthritis Outcome Score; KOOS, Fat mass index; FMI) were examined. RESULTS: Participant median age was 22.3 years (range 16-26) and 63% were female. Although there was no difference in COMP levels between previously injured and uninjured females, previously injured males demonstrated an ∼15% greater (171.5 ng/ml, 95% CI 11.0-428.0, P = 0.04) serum COMP level than uninjured males. However after controlling for FMI, this difference was absent. Within the injured participants, COMP levels were associated with MOAKSSYNOVITIS and FMI. Furthermore, COMP fragmentation patterns were distinct between injured and uninjured individuals. CONCLUSIONS: In this study group, serum COMP levels were greater in injured males, but not females, compared to matched controls. However, after controlling for FMI, no differences in COMP were observed. A unique COMP fragmentation pattern was observed in injured vs uninjured participants. These results further the hypothesis that COMP levels and/or degradation of the protein may be a marker of cartilage injury which could predispose to later OA.

Differences in subchondral bone plate and cartilage thickness between women with anterior cruciate ligament reconstructions and uninjured controls.

OBJECTIVE: Anterior cruciate ligament (ACL) tears increase early onset osteoarthritis (OA) risk leading to cartilage and bone degradation. While the contribution of bone in OA development is unclear, evidence suggests that bone changes accompany cartilage degradation. This study aims to assess if regions with differences in subchondral bone plate thickness have differences in cartilage thickness when comparing ACL reconstructed (ACLR) knees of women ≥5 years post-injury to contralateral and controls with uninjured knees. DESIGN: Magnetic resonance imaging (MRI) assessed cartilage and high resolution peripheral quantitative computed tomography (HR-pQCT) assessed subchondral bone in both knees. Multimodal 3D image registration aligned anatomy. Maps of the spatial distribution of thickness on the articular surfaces were generated to compare women with ACL reconstructions to contralateral and controls with uninjured knees. RESULTS: ACLR knees had a thicker subchondral bone plate in the posterior and central lateral femur compared to contralateral knees (10.4% and 4.2% thicker, P = 0.032 and 0.032, W = 108 and 107, respectively) and in the posterior lateral femur compared to control knees (17.1% thicker, P = 0.014, W = 177). Cartilage differences were not detected (P > 0.05) in these regions. CONCLUSIONS: This study demonstrates that subchondral bone plate thickness differences are prominent following knee injury, as measured by HR-pQCT, but no statistically significant differences in cartilage morphology, measured by MRI, were found between ACLR knees compared to contralateral and control knees. These data provide novel insight into post-traumatic knee injuries that may be signs of early OA pathogenesis.

Knee confidence in youth and young adults at risk of post-traumatic osteoarthritis 3-10 years following intra-articular knee injury.

OBJECTIVES: To examine differences in knee confidence between individuals with a history of youth sport-related knee injury and uninjured controls. DESIGN: Historical cohort study. METHODS: Participants include 100 individuals who sustained a youth sport-related intra-articular knee injury 3-10 years previously and 100 age-, sex- and sport-matched uninjured controls. Outcomes included: Knee confidence (Knee Osteoarthritis and Outcome Score); fat mass index (FMI; dual-energy X-ray absorptiometry); and weekly physical activity (modified Godin-Shephard Leisure Time Questionnaire). Mean within-pair differences (95% CI) were calculated for all outcomes. Unadjusted and adjusted (FMI and physical activity) conditional (matched-design) logistic regression (OR 95% CI) examined the association between injury history and knee confidence. RESULTS: Median age of participants was 22 years (range 15-26) and median age at injury was 16 years (range 9-18). Forty-nine percent (95% CI; 39.0, 59.0) of previously injured participants were bothered by knee confidence, compared to 12% (5.5, 18.5) of uninjured participants. Although there was no between group difference in physical activity, injured participants had higher FMI compared to controls (within-pair difference; (95% CI): 1.05kg/m2; (0.53, 1.57)). Logistic regression revealed that injured participants had 5.0 (unadjusted OR; 95% CI; 2.4, 10.2) and 7.5 times (adjusted OR; 95% CI: 2.7, 21.1) greater odds of being bothered by knee confidence than controls. CONCLUSIONS: Knee confidence differs between individuals with a previous youth sport-related knee injury and healthy controls. Knee confidence may be an important consideration for evaluating osteoarthritis risk after knee injury and developing secondary prevention strategies.

Validity of the SMS, Phone, and medical staff Examination sports injury surveillance system for time-loss and medical attention injuries in sports.

The accurate measurement of sport exposure time and injury occurrence is key to effective injury prevention and management. Current measures are limited by their inability to identify all types of sport-related injury, narrow scope of injury information, or lack the perspective of the injured athlete. The aims of the study were to evaluate the proportion of injuries and the agreement between sport exposures reported by the SMS messaging and follow-up telephone part of the SMS, Phone, and medical staff Examination (SPEx) sports injury surveillance system when compared to measures obtained by trained on-field observers and medical staff (comparison method). We followed 24 elite adolescent handball players over 12 consecutive weeks. Eighty-six injury registrations were obtained by the SPEx and comparison methods. Of them, 35 injury registrations (41%) were captured by SPEx only, 10 injury registrations (12%) by the comparison method only, and 41 injury registrations (48%) by both methods. Weekly exposure time differences (95% limits of agreement) between SPEx and the comparison method ranged from -4.2 to 6.3 hours (training) and -1.5 to 1.0 hours (match) with systematic differences being 1.1 hours (95% CI 0.7 to 1.4) and -0.2 (95% CI -0.3 to -0.2), respectively. These results support the ability of the SPEx system to measure training and match exposures and injury occurrence among young athletes. High weekly response proportions (mean 83%) indicate that SMS messaging can be used for player measures of injury consequences beyond time-loss from sport. However, this needs to be further evaluated in large-scale studies.

Running injuries in novice runners enrolled in different training interventions: a pilot randomized controlled trial.

The purpose of this trial was to evaluate injury risk in novice runners participating in different strength training interventions. This was a pilot randomized controlled trial. Novice runners (n = 129, 18-60 years old, <2 years recent running experience) were block randomized to one of three groups: a "resistance" strength training group, a "functional" strength training group, or a stretching "control" group. The primary outcome was running related injury. The number of participants with complaints and the injury rate (IR = no. injuries/1000 running hours) were quantified for each intervention group. For the first 8 weeks, participants were instructed to complete their training intervention three to five times a week. The remaining 4 months was a maintenance period. TRIAL REGISTRATION: NCT01900262. A total of 52 of the 129 (40%) novice runners experienced at least one running related injury: 21 in the functional strength training program, 16 in the resistance strength training program and 15 in the control stretching program. Injury rates did not differ between study groups [IR = 32.9 (95% CI 20.8, 49.3) in the functional group, IR = 31.6 (95% CI 18.4, 50.5) in the resistance group, and IR = 26.7 (95% CI 15.2, 43.2)] in the control group. Although this was a pilot assessment, home-based strength training did not appear to alter injury rates compared to stretching. Future studies should consider methods to minimize participant drop out to allow for the assessment of injury risk. Injury risk in novice runners based on this pilot study will inform the development of future larger studies investigating the impact of injury prevention interventions.

OARSI Clinical Trials Recommendations: Design and conduct of clinical trials for primary prevention of osteoarthritis by joint injury prevention in sport and recreation.

The risk of post-traumatic osteoarthritis (PTOA) substantially increases following joint injury. Research efforts should focus on investigating the efficacy of preventative strategies in high quality randomized controlled trials (RCT). The objective of these OARSI RCT recommendations is to inform the design, conduct and analytical approaches to RCTs evaluating the preventative effect of joint injury prevention strategies. Recommendations regarding the design, conduct, and reporting of RCTs evaluating injury prevention interventions were established based on the consensus of nine researchers internationally with expertise in epidemiology, injury prevention and/or osteoarthritis (OA). Input and resultant consensus was established through teleconference, face to face and email correspondence over a 1 year period. Recommendations for injury prevention RCTs include context specific considerations regarding the research question, research design, study participants, randomization, baseline characteristics, intervention, outcome measurement, analysis, implementation, cost evaluation, reporting and future considerations including the impact on development of PTOA. Methodological recommendations for injury prevention RCTs are critical to informing evidence-based practice and policy decisions in health care, public health and the community. Recommendations regarding the interpretation and conduct of injury prevention RCTs will inform the highest level of evidence in the field. These recommendations will facilitate between study comparisons to inform best practice in injury prevention that will have the greatest public health impact.

Outcomes associated with early post-traumatic osteoarthritis and other negative health consequences 3-10 years following knee joint injury in youth sport.

OBJECTIVE: Post-traumatic osteoarthritis (PTOA) commonly affects the knee joint. Although the risk of PTOA substantially increases post-joint injury, there is little research examining PTOA outcomes early in the period between joint injury and disease onset. Improved understanding of this interval would inform secondary prevention strategies aimed at preventing and/or delaying PTOA progression. This study examines the association between sport-related knee injury and outcomes related to development of PTOA, 3-10 years post-injury. DESIGN: This preliminary analysis of the first year of a historical cohort study includes 100 (15-26 years) individuals. Fifty with a sport-related intra-articular knee injury sustained 3-10 years previously and 50 uninjured age, sex and sport matched controls. The primary outcome was the 'Symptoms' sub-scale of the Knee Osteoarthritis and Injury Outcome Score (KOOS). Secondary outcomes included; the remaining KOOS subscales, body mass index (BMI), hip abductor/adductor and knee extensor/flexor strength, estimated aerobic capacity (VO2max) and performance scores on three dynamic balance tests. Descriptive statistics (mean within-pair difference; 95% Confidence interval (CI) and conditional odds ratio (OR, 95% CI; BMI) were used to compare study groups. RESULTS: Injured participants demonstrated poorer KOOS outcomes [symptoms -9.4 (-13.6, -5.2), pain -4.0 (-6.8, -1.2), quality-of-life -8.0 (-11.0, -5.1), daily living -3.0 (-5.0, -1.1) and sport/recreation -6.9 (-9.9, -3.8)], were 3.75 times (95% CI 1.24, 11.3) more likely to be overweight/obese and had lower triple single leg hop scores compared to controls. No significant group differences existed for remaining balance scores, estimated VO2max, hip or knee strength ratios or side-to-side difference in hip abductor/adductor or quadricep/hamstring strength. CONCLUSIONS: This study provides preliminary evidence that youth/young adults following sport-related knee injury report more symptoms and poorer function, and are at greater risk of being overweight/obese 3-10 years post-injury compared to matched uninjured controls.

Female soccer knee injury: observed knowledge gaps in injury prevention among players/parents/coaches and current evidence (the KNOW study).

This study sought to determine if knowledge regarding the risk for knee injuries and the potential for their prevention is being translated to female adolescent soccer players (13-18 years), their parents, and coaches. Eligible participants in the 2007 indoor soccer season were surveyed to determine their knowledge of the risk for and the potential to prevent knee injuries, and their knowledge of effective prevention strategies, if they felt that injury prevention was possible. Team selection was stratified to be representative of both competitive and recreational level play and age group distributions within the selected soccer association. Of the study subjects, 773/1396 (55.4%) responded to the survey: 408 (53%) players, 292 (38%) parents, and 73 (9%) coaches. Most respondents (538 [71%]) were aware of the risk for knee injury. Coaches and parents were more likely than players to view knee injuries as preventable; however, appropriate prevention strategies were often not identified. Four hundred eighty-four (63.8%) respondents reported that they had never received information on knee injuries. Substantial knowledge gaps regarding knee injury prevention and effective preventative strategies were identified. Given the predominance of knee injuries in female adolescent soccer players, there is an urgent need for knowledge translation of prevention strategies to decrease both incidence and long-term consequences of knee injuries.

Examining the effect of the injury definition on risk factor analysis in circus artists.

A secondary data analysis of a prospective cohort study was conducted to explore how different definitions of injury affect the results of risk factor analyses. Modern circus artists (n=1281) were followed for 828,547 performances over a period of 49 months (2004-2008). A univariate risk factor analysis (age, sex, nationality, artist role) estimating incidence rate ratios (IRR) with 95% confidence intervals (95% CI) was conducted using three injury definitions: (1) medical attention injuries, (2) time-loss injuries resulting in ≥1 missed performances (TL-1) and (3) time-loss injuries resulting in >15 missed performances (TL-15). Results of the risk factor analysis were dependent on the injury definition. Sex (females to male; IRR=1.13, 95% CI; 1.02-1.25) and age over 30 (<20 years to >30 years; IRR=1.37, 95% CI; 1.07-1.79) were risk factors for medical attention injuries only. Risk of injury for Europeans compared with North Americans was higher for TL-1 and TL-15 injuries compared with medical attention injuries. Finally, non-sudden load artists (low-impact acts) were less likely than sudden load artists (high-impact acts) to have TL-1 injuries, but the risk of medical attention injuries was similar. The choice of injury definition can have effects on the magnitude and direction of risk factor analyses.

The effectiveness of a neuromuscular prevention strategy to reduce injuries in youth soccer: a cluster-randomised controlled trial.

BACKGROUND: Soccer is a leading sport for participation and injury in youth. OBJECTIVE: To examine the effectiveness of a neuromuscular prevention strategy in reducing injury in youth soccer players. DESIGN: Cluster-randomised controlled trial. SETTING: Calgary soccer clubs (male or female, U13-U18, tier 1-2, indoor soccer). PARTICIPANTS: Eighty-two soccer teams were approached for recruitment. Players from 60 teams completed the study (32 training (n=380), 28 control (n=364)). INTERVENTION: The training programme was a soccer-specific neuromuscular training programme including dynamic stretching, eccentric strength, agility, jumping and balance (including a home-based balance training programme using a wobble board). The control programme was a standardised warm-up (static and dynamic stretching and aerobic components) and a home-based stretching programme. MAIN OUTCOME MEASURES: Previously validated injury surveillance included injury assessment by a study therapist. The injury definition was soccer injury resulting in medical attention and/or removal from a session and/or time loss. RESULTS: The injury rate in the training group was 2.08 injuries/1000 player-hours, and in the control group 3.35 injuries/1000 player-hours. Based on Poisson regression analysis, adjusted for clustering by team and covariates, the incidence rate ratios (IRR) for all injuries and acute onset injury were 0.62 (95% CI 0.39 to 0.99) and 0.57 (95% CI 0.35 to 0.91). Point estimates also suggest protection of lower extremity, ankle and knee sprain injuries (IRR=0.68 (95% CI 0.42 to 1.11), IRR=0.5 (95% CI 0.24 to 1.04) and IRR=0.38 (95% CI 0.08 to 1.75)). CONCLUSIONS: A neuromuscular training programme is protective of all injuries and acute onset injury in youth soccer players.

Is there a clinical standing balance measurement appropriate for use in sports medicine? A review of the literature.

The aims of this review paper are (1) to discuss the relevance of proprioception and standing balance in rehabilitation and prevention of sports injuries, (2) to examine the evidence supporting decreased balance as a risk factor and balance training as a prevention strategy for injury in sport, (3) to review the evidence in the literature supporting the reliability and validity of clinical balance measurements, (4) to examine factors potentially influencing lower extremity balance and (5) to discuss the implications for future research in identifying clinical balance measurement tools appropriate for use in rehabilitation and injury prevention in sports medicine. Laboratory measurement techniques for balance (using costly, highly technical, and often non-portable equipment) are often not appropriate for use in a clinical setting or for research in a large field based clinical trial. Many of the clinical tools for balance measurement are not appropriate for use in the healthy active population, as they are not challenging enough or they are static balance measures. Evidence from original research suggests that static unipedal timed balance is a reliable measurement in both children and adults. There is little evidence to support the reliability and validity of dynamic clinical measurements of balance developed. It is impaired dynamic unipedal balance in sport which may be a significant risk factor for re-injury following rehabilitation or injury in sport. Dynamic standing balance measurement tools appropriate for use in the clinical setting need to be developed and assessed for reliability and validity.

Risk factors for groin injuries in hockey.

PURPOSE: The objective of this cohort study was to determine the level of off-season sport specific activity, peak isometric adductor torque, and hip abduction flexibility that are predictive of groin or abdominal strain injury in the National Hockey League (NHL). METHODS: The subjects were 1292 consenting NHL players. Estimated relative risks of injury are reported using the following exposures: 1) level of sport specific training in the off-season, 2) peak isometric adductor torque, 3) total hip abduction flexibility, 4) previous injury, 5) years of NHL experience, and 6) skate blade hollow measurement. Estimates of probability of injury are predicted for various levels of exposures on the basis of logistic regression analysis. RESULTS: During training camp, players who reported less than 18 sessions sport specific training in the off-season were at greater than three times the risk of injury than those who did not (relative risk (RR); 3.38 95% confidence interval (CI), 1.45-7.92). Players who reported previous history of this injury were at more than two times the risk of injury than those who did not (RR, 2.88; 95% CI, 1.33-6.26). Veterans were at greater than five times the risk of injury than rookies (RR, 5.69; 95% CI, 2.05-15.85). Peak isometric adductor torque, total abduction flexibility, and skate blade hollow measurement were not predictive of injury. There is evidence of a dose-response gradient as predicted probability of injury decreases with increasing levels of sport specific training. In the regular season, sport specific training was not as strong a risk factor (RR, 2.32; 95% CI, 1.0-5.39). CONCLUSION: Low levels of off-season sport specific training and previous injury are clearly risks for groin injury at an elite level of hockey. Future research is required to investigate prevention strategies for this injury in hockey.

Groin and abdominal strain injuries in the National Hockey League.

OBJECTIVE: To analyze groin and abdominal strain injuries retrospectively among elite male hockey players in the National Hockey League (NHL) over six seasons of play (1991/92 to 1996/97). DESIGN: Retrospective case series design. SETTING: The NHL. PARTICIPANTS: The NHL participants were an inclusive sample of 7,050 NHL hockey players who played in the NHL from the 1991/92 to the 1996/97 seasons. A subset of 2,600 NHL hockey players who played from the 1995/96 to the 1996/97 seasons was further analyzed. MAIN OUTCOME MEASURES: The injury definition for groin/abdominal strain injury included any injury recorded as a muscle strain injury involving a muscle in any of the abdominal, hip flexor, or hip adductor muscle groups. Femoral, abdominal, and inguinal hernias were also included. Cumulative incidence rates over six seasons of play in the NHL and incidence densities over two seasons of play in the NHL are reported. Specific injury parameters examined included muscle region, time in season, type of session, reinjury, time period in session, position of play, player's experience, mechanism of injury, and time loss. RESULTS: A total of 617 groin/abdominal strain injuries were reported in the NHL over six seasons of play. The cumulative incidence rate in the NHL increased over 6 years of play from 12.99 injuries/100 players/year in the 1991/92 season to 19.87 injuries/100 players/year in the 1996/97 season. The rate of increase was 1.32 (95% confidence interval -0.58, 3.21) injuries/100 players/year. The incidence density of groin/abdominal injury during NHL training camp was five times that during the regular season and 20 times that during the postseason. The incidence density in the NHL during games was six times that during practice. The majority of injuries reported were adductor groin muscle strains. The proportion of injuries reported that were recurrent was 23.5%. There was no significant difference in proportion of injuries reported by time period within a session. The mechanism of injury recorded was noncontact in nature in >90% of injuries reported. Mean time loss due to injury was significantly greater for abdominal injuries (10.59 sessions) than for groin injuries (6.59 sessions). A conservative estimate of the impact of groin/abdominal injury on each NHL team is a game loss of 25 player games/year. CONCLUSION: The impact of groin and abdominal strain injury at an elite level of play in hockey is significant and increasing. Future research in this area is needed to identify risk factors and potentially implement prevention strategies to reduce groin and abdominal strain injury at all levels of play.

Test-retest reliabilty of isokinetic hip adductor and flexor muscle strength.

OBJECTIVE: To determine the test-retest reliability of eccentric hip flexor and adductor peak torque and endurance using a Cybex Norm isokinetic dynamometer and to evaluate muscle soreness after exercise as a result of the testing procedure. DESIGN: Prospective test-retest reliability study. PARTICIPANTS: A total of 19 male volunteers (21-43 years old). INTERVENTION: Tests included hip flexor and adductor peak torque strength measured at 60 degrees/s (concentric and eccentric) and endurance measurements (total work done over 20 continuous concentric/eccentric contractions at 150 degrees/s). Subjects were tested on three occasions at 1-week intervals. MAIN OUTCOME MEASURES: Repeated measures analysis of variance was performed for all dependent variables including the subject's dominant and nondominant side among the three test sessions. Intraclass correlation coefficients (ICCs) were calculated to compare the data between sessions. In addition, simple linear regression analysis was completed to determine the relationship between session measurements for all measures with ICC > 0.75. RESULTS: The main findings of this study are that eccentric peak hip adductor torque was reliably measured on a Cybex Norm isokinetic dynamometer using a continuous eccentric/ concentric cycle protocol at a speed of 60 degrees/s (ICC > 0.84). Peak concentric adductor torque and peak eccentric and concentric hip flexor torque were less reliable using the same protocol (ICC < 0.67). Endurance measurements, using total work done over 20 repetitions, were not reliable for hip flexor and adductor muscle groups using a continuous eccentric/concentric cycle protocol at a speed of 150 degrees/s (ICC < 0.55). Posttest muscle soreness was found to be of significant concern with such a protocol. CONCLUSION: The results from this test-retest reliability study confirm the reliability of eccentric peak hip adductor torque measurements for use clinically and in future research. In addition, the need to assess posttest muscle soreness after isokinetic muscle testing is confirmed.