Athletic Training and Sports Health Care

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Original Research 

Hamstring Strain Incidence Between Genders and Sports in NCAA Athletics

Kevin M. Cross, MS, ATC, PT; Kelly K. Gurka, PhD; Mark Conaway, PhD; Christopher D. Ingersoll, PhD, ATC

Abstract

Anecdotal evidence suggests that athletes who play sports requiring explosive activities are more susceptible to hamstring strain. No published studies exist that compare the incidence of hamstring strain between genders or sports. Thus, the purpose of this study is to compare those rates between genders and sports during the 2004–2007 National Collegiate Athletic Association (NCAA) athletic seasons. Data were acquired from the NCAA Injury Surveillance System. Incidence rate ratios (IRRs) comparing hamstring strains between genders and sports were calculated. Male athletes have a higher rate of hamstring strain (IRR = 1.62; 95% CI, 1.28–2.05), and men’s sports of soccer (6.91 injuries/10,000 athlete-exposures [AEs]) and football (6.04 injuries/10,000 AEs) and women’s sports of soccer (3.81 injuries/10,000 AEs) and field hockey (3.79/10,000 AEs) experience the highest rates of hamstring strain. Efforts to create preventive and rehabilitation programs might be more appropriately focused on student athletes who participate in soccer, football, and field hockey, especially among men.

Abstract

Anecdotal evidence suggests that athletes who play sports requiring explosive activities are more susceptible to hamstring strain. No published studies exist that compare the incidence of hamstring strain between genders or sports. Thus, the purpose of this study is to compare those rates between genders and sports during the 2004–2007 National Collegiate Athletic Association (NCAA) athletic seasons. Data were acquired from the NCAA Injury Surveillance System. Incidence rate ratios (IRRs) comparing hamstring strains between genders and sports were calculated. Male athletes have a higher rate of hamstring strain (IRR = 1.62; 95% CI, 1.28–2.05), and men’s sports of soccer (6.91 injuries/10,000 athlete-exposures [AEs]) and football (6.04 injuries/10,000 AEs) and women’s sports of soccer (3.81 injuries/10,000 AEs) and field hockey (3.79/10,000 AEs) experience the highest rates of hamstring strain. Efforts to create preventive and rehabilitation programs might be more appropriately focused on student athletes who participate in soccer, football, and field hockey, especially among men.

Mr Cross is from the University of Virginia, Sports Medicine Program; Drs Gurka and Conaway are from the University of Virginia School of Medicine, Charlottesville, Va. Dr Ingersoll is from the The Herbert H. and Grace A. Dow College of Health Professions, Central Michigan University, Mount Pleasant, Mich.

The authors have no financial or proprietary interest in the materials presented herein.

Address correspondence to Kevin Cross, MS, ATC, PT, 5004 Madison Court, Charlottesville, VA 22911; e-mail: kmc7e@virginia.edu.

Received: August 13, 2009
Accepted: January 26, 2010

Hamstring strain is one of the most common musculoskeletal diagnoses in sport, and the prevalence of reoccurrence is as high as 34%.1–12 The immediate impact has been reported in soccer and Australian rules football, as athletes who injure a hamstring miss approximately 18 days of participation and approximately 3 competitions per injury.13 Due to the impact of a hamstring injury, numerous attempts to identify risk factors or justify intervention programs within specific sports have been made.6,14–21 Unfortunately, continued uncertainty with regard to the etiology of hamstring strains persists, making it difficult to identify where efforts to develop preventive and management programs would be most valuable.

Most perceptions of the etiology and management of hamstring strains have been driven by anecdotal experience. Clinicians often associate hamstring injuries with sports that emphasize explosive activities, such as sprinting and jumping, as well as rapid acceleration and deceleration.22 Only anecdotal evidence supports the premise that most hamstring strains occur in explosive sports. The literature contains injury surveillance from specific sports, especially soccer and Australian rules football, but to our knowledge, no studies currently exist that compare sports with regard to the incidence of hamstring strain.1–4,6–11,22 If differences in incidence between sports do exist, further research may be performed to determine whether sport-specific interventions are required.

Of the few studies that have investigated hamstring strains among specific sports, the vast majority of injury surveillance studies have been conducted among men. Patterns of hamstring strains in women’s sports have not been adequately studied to validate the assumption of similar injury characteristics between genders.23 If patterns of hamstring strain are different between the genders, then gender-specific approaches to the prevention and treatment of hamstring strains may be required for optimal results.

Currently, no studies exist that compare hamstring strain incidence across genders and sports. Describing the patterns of hamstring injury within each of these categories may contribute to the development of future analytical research regarding risk factors and preventive or rehabilitative programs. The National Collegiate Athletic Association (NCAA) Injury Surveillance System (ISS), a Web-based system that collects injury data from trained medical personnel, represents a valuable potential source of data regarding hamstring strains across sports and genders. Its database of injury data for both genders and multiple sports across all divisions of the NCAA makes it the largest surveillance system for collegiate sports in the United States and unparalleled in its scope.24 Therefore, the purpose of this article is to compare the incidence rates of hamstring strain between genders and sports among collegiate student athletes using data from the NCAA ISS. We hypothesize that male athletes will have higher incidence rates of hamstring strain than female athletes and that those student athletes who participate in sports that require repeated sprinting will experience higher incidences of hamstring strain.

Methods

This research uses 2004–2007 academic-year data from the NCAA ISS. We ascertained the number of hamstring strains and the number of student athlete exposures (AEs) for each division of each sport from the Detailed Injury Summary Reports. These reports were accessed via the NCAA ISS Web site. A member of the NCAA ISS was contacted to clarify any questionable data in the reports. Due to direct data acquisition from the NCAA ISS, the operational definitions for hamstring strain and student athlete exposure are identical to those provided by the NCAA ISS.

The NCAA ISS collects exposure and injury data from a national sample of NCAA institutions for many sports via an Internet-based application. Details of this system including sampling and data collection methods are outlined in detail elsewhere.25 A sample of Division I, II, and III institutions volunteered to provide data to the NCAA ISS for 17 different sports (men: baseball, basketball, cross country, football, lacrosse, soccer, tennis, and wrestling; women: basketball, crew, cross country, field hockey, lacrosse, soccer, softball, tennis, and volleyball). Data for each injury event, as well as those for AEs, are entered by trained members of the medical staff at each participating institution for the duration of the applicable playing season during each academic year. The NCAA regularly monitors data entry for quality assurance.

For each injury entered in the NCAA ISS, both the injured body part and type of injury are specified. Per the NCAA ISS definition, a hamstring injury was reported if it was caused by an activity in an organized intercollegiate practice or competition that resulted in the inability to participate in competition for at least 1 day. Possible hamstring injuries include complete tear, contusion, myositis ossificans, partial tear, spasm, and tendonitis. Only hamstring injuries classified as partial tears or complete tears and diagnosed by a certified athletic trainer or physician were included in this analysis. Because no hamstring injuries were reported for women’s crew, this sport was excluded.

A single AE was defined by the NCAA ISS as one student athlete participating in one practice or competition. The designation of an AE gave no consideration to the amount of time that the student athlete participated in the event. During games, an AE was counted only for those student athletes who accrued playing time.

Statistical Analysis

The frequency of hamstring strain by gender and sport were tabulated, and incidence rates (IRs) were calculated. Poisson regression was used to calculate incidence rate ratios (IRRs) and their corresponding 95% confidence interval (CI). These models are appropriate for analyzing a count of a number of events (ie, hamstring injuries) relative to a number of exposures. As in standard regression, Poisson regression can be used to estimate the independent effect of one factor, gender, on the IRRs, adjusting for other factors such as sport and NCAA division. In addition, these models can be applied separately to men’s and women’s sports, allowing us to compare sports adjusting for NCAA division. As in standard regression analyses, any of the these comparisons can be obtained from the estimated coefficients in the regression model.26 A scale factor was used to correct for models in which the data were overdispersed, allowing us to relax one of the restrictive assumptions of Poisson models. With the scale factor, the models are based on the assumption that the standard deviation of the counts is proportional, not necessarily equal, to the mean.27

The IRR is the ratio of the incidence rate in one level of exposure (eg, males) to the incidence rate in the referent level of the exposure (eg, females). When the IRR is <1, members in the exposed group (eg, males) experience a lower rate of the outcome (eg, hamstring injury) compared with the referent group (eg, females). In contrast, when the IRR is >1, the exposed group (eg, males) experiences a greater rate of the outcome (eg, hamstring injury) than does the referent group (eg, females). If the 95% CI includes the value of 1 (ie, the value at which the incidence rates of the outcome are equal, among males and females for example), there is no significant difference in the likelihood of sustaining a hamstring strain between the 2 exposure groups at the alpha level of 0.05. Analyses were performed using SAS version 9.1 software (SAS Institute, Inc, Cary, NC).

Results

A total of 1,576 hamstring strains and 4,046,188 AEs were reported during the study period. Men were 62% more likely than women to have sustained a hamstring strain (IRR = 1.62; 95% CI, 1.28–2.05) (Table 1).

Hamstring Strains and Estimated Adjusted Incidence Rate Ratios for Gender, National Collegiate Athletic Association Injury Surveillance System, 2004–2007 Athletic Seasons

Table 1: Hamstring Strains and Estimated Adjusted Incidence Rate Ratios for Gender, National Collegiate Athletic Association Injury Surveillance System, 2004–2007 Athletic Seasons

Rates of hamstring strain were highest among student athletes playing soccer among both men (0.691 hamstring strains/1000 AEs) and women (0.381 hamstring strains/1000 AEs). Therefore, to compare the incidence rates among sports, the referent group to calculate IRRs for both genders was soccer. Men playing all sports, except football, were significantly less likely to sustain a hamstring strain compared with men playing soccer (Table 2). Among women, student athletes playing all sports, except field hockey, tennis, and cross country, experienced a significantly lower rate of hamstring strain compared with women playing soccer (Table 2).

Hamstring Strains with Associated Incidence Rate Ratios for Sport Among Men and Women, National Collegiate Athletic Association Injury Surveillance System, 2004–2007 Athletic Seasons

Table 2: Hamstring Strains with Associated Incidence Rate Ratios for Sport Among Men and Women, National Collegiate Athletic Association Injury Surveillance System, 2004–2007 Athletic Seasons

Discussion

On the basis of these findings, male athletes have a higher incidence rate of hamstring strains than do female athletes. Regardless of gender, student athletes participating in soccer had the greatest risk of hamstring strains. Among male athletes, football has a comparable incidence rate of hamstring strains to soccer. Among female athletes, student athletes who play field hockey have a comparable incidence rate of hamstring strains to soccer.

Gender

This study suggests that male athletes are more likely to sustain a hamstring strain than female athletes. On the basis of a previous literature review, Worrell28 proposed 4 major factors that interact to predispose an athlete to a hamstring strain: decreased flexibility, increased fatigue, decreased strength, and inadequate warm-up. These factors were derived from anecdotal observations and retrospective research that compared injured athletes to noninjured athletes. Such retrospective research designs dominated the literature at the time of the article’s publication. Currently, the focus of preventive and rehabilitation programs and research interests of muscle injuries continue to revolve around these 4 characteristics in addition to the potential effects of muscle stiffness. For 3 of these factors, the literature suggests potential differences between the genders.

Several investigations have assessed the influence of gender on hamstring muscle length in large samples of healthy individuals.29–31 Youdas et al29 and Trehearn and Buresh31 assessed the hamstring muscle length by passive measurements. Blackburn et al30 assessed the muscles’ extensibility during an active knee extension. Under both conditions, men had significantly less flexibility of the hamstring muscles than did women.

Similarly, male hamstring muscles have increased muscle stiffness compared with female hamstring muscles.32,33 As a consequence, the hamstring has less length change and less time to absorb the energy imposed during an eccentric contraction that occurs during the swing phase of gait. Wilson et al34 described this loss of “cushioning” as a major factor inducing trauma to the muscle tissue. The influence of stiffness on the mechanics of acute muscle injury has been supported in the animal model.35

Basic science research suggests that men generally exhibit physiological responses to muscle fatigue more quickly than do women during both static and dynamic activity.36–39 Billaut and Bishop39 specifically reviewed the literature’s fatigue data accrued following repeated sprint workouts. Because men generally have larger body mass and thus a larger workload for an activity of equivalent intensity and volume, data were normalized to the workload. The normalized results indicate minimal differences in the physiological factors of fatigue between genders. The higher workload among men due to body dimensions and power output create larger energy deficits compared with women, independent of gender-specific physiology.39 Further research that prospectively accounts for the effect of such confounding factors on fatigue measures is necessary for a conclusive assessment of fatigue differences between genders.

The effect of gender on muscle strength is equivocal depending on the variable used to normalize the strength measure. Some research supports significantly stronger knee flexors in men when normalized to the subject’s body weight.40–41 Also, increased hamstring strength among men is implied from larger hamstring to quadriceps ratios during isokinetic testing, especially at faster contraction speeds.42–45 However, when normalized to the muscle’s cross-sectional area, no difference in knee flexor strength between the genders has been identified.46 Regardless, systematic reviews have reported the exclusive influence of hamstring strength on hamstring strains to be inconclusive.47,48

Although the mechanisms by which men are more susceptible to hamstring injury remains unclear, these findings have implications for designing future research on injury prevention and rehabilitation programs. Muscle flexibility and stiffness appear to be conclusively disparate between genders, as men have less flexibility and greater stiffness. The importance of strength and fatigue for explaining the differences in the incidence rate of hamstring strains among genders is inconclusive. The injury model proposed by Worrell28 that emphasizes the interaction of these factors, as well as the inclusion of untested entities, may provide better insight to the different incidences of hamstring strains among genders.

Sport

For both men and women, the incidence of hamstring strain was greatest among student athletes playing soccer. Among men, only those playing football sustained comparable rates of hamstring strains. In women’s sports, only field hockey had rates of hamstring strain comparable to soccer. Although the incidence rates of hamstring strain among women playing tennis and cross country are considerably lower than among women playing soccer, the study did not demonstrate a significant difference, likely due to a lack of statistical power indicated by the wide confidence intervals around both of the incidence rate ratios.

These findings are consistent with anecdotal evidence and suggest that explosive activities, common during sports such as soccer, football, and field hockey, increase the risk of hamstring strain. Specifically, these sports require repeated bouts of sprinting for long distances. Rampinini et al49 reported that, athletes run a distance of approximately 11,000 meters during soccer matches, of which approximately 2,700 meters (24.5% of the total distance) are at a high intensity and approximately 900 meters (8.1% of the total distance) are at a very high intensity. Because the hamstring muscles are suggested to be composed predominantly of fast-twitch muscle fiber and more likely to fatigue, the energy requirement to repetitively contract during running and sprinting may make the athlete more susceptible to injury.50

Similarly, most of the sports with a significantly higher incidence of hamstring strain have relatively long periods of uninterrupted play. Considering football, players often participate in multiple successive plays, and although 40 seconds is allowed between each play, the entire time is frequently not used. Student athletes who play skill positions (ie, running back, wide receiver, defensive back) are most likely to perform maximal and submaximal sprinting activities on each play and they have also been reported to sustain the greatest number of hamstring strains among football position players.12 The unique sport characteristics of repeated submaximal contractions at a fast speed in conjunction with minimal rest periods may need to be considered when formulating preventive and rehabilitative programs.

Among women, only student athletes playing field hockey experienced rates of hamstring strain comparable to student athletes playing soccer. In addition to similar sport characteristics such as field size, substitution patterns, and game flow, field hockey requires the athletes’ playing posture to emphasize trunk flexion. This posture has been suggested to be an additional predisposition to hamstring strain.51,52

Strengths and Limitations

This is the largest database study of hamstring strains reported in the literature and the first study to report the incidence of hamstring strain by gender and sport. Although the findings generally support anecdotal evidence, interesting nuances to the distribution of hamstring strain were identified. Specifically, athletes who participate in sports with minimal rest periods and emphasize repeated sprints appear more likely to sustain a hamstring strain. In addition, other factors that may have affected the rate of hamstring injury, such as weekly training load and age, are consistent across the study population due to the NCAA rules. Therefore, their influence on the study’s results should not be significant.

Our study used a preexisting database to determine the incidence of hamstring strains. Thus, we had no control over the definitions for hamstring strain or AE. An inclusion of greater AE detail as described by Fuller et al53 may have influenced the incidence rate calculations and the consequent comparisons among genders and sports. Also, data were not collected on all NCAA-sanctioned sports. Specifically, injury and exposure data were not collected for student athletes involved in track and field events. Given the nature of sprinting, middle distance running events, and jumping events, a study of hamstring strain among track and field athletes should be conducted. Despite efforts to achieve a nationally representative sample, participation in ISS is voluntary. Thus, participating institutions may not adequately represent the incidence of hamstring injury among American collegiate student athletes.

Clinical Implications

Because there is no consensus regarding the etiology and treatment of hamstring injuries, we preformed a descriptive epidemiologic study in a very large cohort to examine general patterns of hamstring strain. Hamstring strain incidence rates between sports and genders have not previously been reported. Because of potential differences in the risk of hamstring strain between various subgroups (ie, gender and sports), we do not believe that it is appropriate to combine descriptive injury data from genders or various sports to analyze the specific injury characteristics (ie, injury mechanism) without evidence of commonality. Given our results of a significant difference in the incidence of hamstring strain between genders, future research should compare the specific injury characteristics of hamstring strain between genders. To minimize the potential for confounding, gender differences should be analyzed within a common sport.

Injury characteristics, especially of anterior cruciate ligament sprains, have been a focus for sports medicine research. The results have led to the development of successful female-focused prevention programs to address risk factors that are more prevalent among women. Similarly, clinicians and researchers have developed hamstring prevention programs based on the best evidence and observations within specific sports.6,14,54,55 Given our findings, such strategies to create gender-specific programs for preventing hamstring strains may be warranted as well. Then, clinical research may investigate the effectiveness of such sport and gender-based prevention programs for hamstring strains.

References

  1. Shawdon A, Brukner P. Injury profile of amateur Australian rules footballers. Aust J Sci Med Sport. 1994;26:59–61.
  2. Seward H, Orchard J, Hazard H, Collinson D. Football injuries in Australia at the elite level. Med J Aust. 1993;159:298–301.
  3. Volpi P, Melegati G, Tornese D, Bandi M. Muscle strains in soccer: A five-year survey of an Italian major league team. Knee Surgery Sports Traumatology Arthroscopy. 2004;12:482–485. doi:10.1007/s00167-003-0478-0 [CrossRef]
  4. Woods C, Hawkins RD, Maltby S, Hulse M, Thomas A, Hodson A. The football association medical research programme: An audit of injuries in professional football—analysis of hamstring injuries. Br J Sports Med. 2004;38:36–41. doi:10.1136/bjsm.2002.002352 [CrossRef]
  5. Brooks JHM, Fuller CW. The influence of methodological issues on the results and conclusions from epidemiological studies of sports injuries—illustrative examples. Sports Medicine. 2006;36:459–472. doi:10.2165/00007256-200636060-00001 [CrossRef]
  6. Arnason A, Andersen TE, Holme I, Engebretsen L, Bahr R. Prevention of hamstring strains in elite soccer: An intervention study. Scand J Med Sci Sports. 2008;18:40–48.
  7. Croisier JL, Forthomme B, Namurois MH, Vanderthommen M, Crielaard JM. Hamstring muscle strain recurrence and strength performance disorders. Am J Sports Med. 2002;30:199–203.
  8. Hawkins RD, Fuller CW. A prospective epidemiological study of injuries in four English professional football clubs. Br J Sports Med. 1999;33:196–203. doi:10.1136/bjsm.33.3.196 [CrossRef]
  9. Hawkins RD, Fuller CW. Risk assessment in professional football: An examination of accidents and incidents in the 1994 World Cup finals. Br J Sports Med. 1996;30:165–170. doi:10.1136/bjsm.30.2.165 [CrossRef]
  10. Morgan BE, Oberlander MA. An examination of injuries in Major League Soccer. The inaugural season. Am J Sports Med. 2001;29:426–430.
  11. Orchard J, Seward H. Epidemiology of injuries in the Australian football league, seasons 1997–2000. Br J Sports Med. 2002;36:39–44. doi:10.1136/bjsm.36.1.39 [CrossRef]
  12. Feeley BT, Kennelly S, Barnes RP, et al. Epidemiology of National Football League training camp injuries from 1998 to 2007. Am J Sports Med. 2008. doi:10.1177/0363546508316021 [CrossRef]
  13. Petersen J, Holmich P. Evidence based prevention of hamstring injuries in sport. Br J Sports Med. 2005;39:319–323. doi:10.1136/bjsm.2005.018549 [CrossRef]
  14. Askling C, Karlsson J, Thorstensson A. Hamstring injury occurrence in elite soccer players after preseason strength training with eccentric overload. Scand J Med Sci Sports. 2003;13:244–250. doi:10.1034/j.1600-0838.2003.00312.x [CrossRef]
  15. Croisier JL, Forthomme B, Namurois MH, Vanderthommen M, Crielaard JM. Hamstring muscle strain recurrence and strength performance disorders. Am J Sports Med. 2002;30:199–203.
  16. Gabbe BJ, Bennell KL, Finch CF, Wajswelner H, Orchard JW. Predictors of hamstring injury at the elite level of Australian football. Scand J Med Sci Sports. 2006;16:7–13. doi:10.1111/j.1600-0838.2005.00441.x [CrossRef]
  17. Mjolsnes R, Arnason A, Osthagen T, Raastad T, Bahr R. A 10-week randomized trial comparing eccentric vs. concentric hamstring strength training in well-trained soccer players. Scand J Med Sci Sports. 2004;14:311–317. doi:10.1046/j.1600-0838.2003.367.x [CrossRef]
  18. Orchard J, Marsden J, Lord S, Garlick D. Preseason hamstring muscle weakness associated with hamstring muscle injury in Australian footballers. Am J Sports Med. 1997;25:81–85. doi:10.1177/036354659702500116 [CrossRef]
  19. Rolls A, George K. The relationship between hamstring muscle injuries and hamstring muscle length in young elite footballers. Physical Therapy in Sport. 2004;5:179–187. doi:10.1016/j.ptsp.2004.08.005 [CrossRef]
  20. Witvrouw E, Danneels L, Asselman P, D’Have T, Cambier D. Muscle flexibility as a risk factor for developing muscle injuries in male professional soccer players. A prospective study. Am J Sports Med. 2003;31:41–46.
  21. Yamamoto T. Relationship between hamstring strains and leg muscle strength. A follow-up study of collegiate track and field athletes. J Sports Med Phys Fitness. 1993;33:194–199.
  22. Brooks JHM, Fuller CW, Reddin DB. Incidence, risk, and prevention of hamstring muscle injuries in professional rugby union. Am J Sports Med. 2006;34:1297–1306. doi:10.1177/0363546505286022 [CrossRef]
  23. Deitch JR, Starkey C, Walters SL, Moseley JB. Injury risk in professional basketball players: A comparison of women’s National Basketball Association and National Basketball Association athletes. Am J Sports Med. 2006;34:1077–1083. doi:10.1177/0363546505285383 [CrossRef]
  24. Dick R, Agel J, Marshall SW. National Collegiate Athletic Association Injury Surveillance System commentaries: Introduction and methods. J Athl Train. 2007;42:173–182.
  25. Appendix B: NCAA injury surveillance system summary. In: NCAA Sports Medicine Handbook. 19th ed. Indianapolis, IN: National Collegiate Athletic Association; 2008:109–110.
  26. Cameron A, Trivedi P. Regression Analysis of Count Data. Cambridge, UK: Cambridge University Press; 1998.
  27. McCullagh P, Nelson J. Generalized Linear Models. 2nd ed. London, UK: Chapman and Hall; 1989.
  28. Worrell TW. Factors associated with hamstring injuries. An approach to treatment and preventative measures. Sports Med. 1994;17:338–345. doi:10.2165/00007256-199417050-00006 [CrossRef]
  29. Youdas JW, Krause DA, Hollman JH, Harmsen WS, Laskowski E. The influence of gender and age on hamstring muscle length in healthy adults. J Orthop Sports Phys Ther. 2005;35:246–252.
  30. Blackburn JT, Padua DA, Riemann BL, Guskiewicz KM. The relationships between active extensibility, and passive and active stiffness of the knee flexors. J Electromyogr Kinesiol. 2004;14:683–691. doi:10.1016/j.jelekin.2004.04.001 [CrossRef]
  31. Trehearn TL, Buresh RJ. Sit-and-reach flexibility and running economy of men and women collegiate distance runners. J Strength Cond Res. 2009;23:158–162.
  32. Blackburn JT, Bell DR, Norcross MF, Hudson JD, Kimsey MH. Sex comparison of hamstring structural and material properties. Clin Biomech (Bristol, Avon). 2009;24:65–70. doi:10.1016/j.clinbiomech.2008.10.001 [CrossRef]
  33. Granata KP, Wilson SE, Padua DA. Gender differences in active musculoskeletal stiffness. part I. Quantification in controlled measurements of knee joint dynamics. J Electromyogr Kinesiol. 2002;12:119–126. doi:10.1016/S1050-6411(02)00002-0 [CrossRef]
  34. Wilson GJ, Wood GA, Elliott BC. The relationship between stiffness of the musculature and static flexibility: An alternative explanation for the occurrence of muscular injury. Int J Sports Med. 1991;12:403–407. doi:10.1055/s-2007-1024702 [CrossRef]
  35. Safran MR, Seaber AV, Garrett WE Jr, . Warm-up and muscular injury prevention. an update. Sports Med. 1989;8:239–249. doi:10.2165/00007256-198908040-00004 [CrossRef]
  36. Hunter SK, Critchlow A, Shin IS, Enoka RM. Men are more fatigable than strength-matched women when performing intermittent submaximal contractions. J Appl Physiol. 2004;96:2125–2132. doi:10.1152/japplphysiol.01342.2003 [CrossRef]
  37. Pincivero DM, Gear WS, Sterner RL, Karunakara RG. Gender differences in the relationship between quadriceps work and fatigue during high-intensity exercise. J Strength Cond Res. 2000;14:202–206. doi:10.1519/1533-4287(2000)014<0202:GDITRB>2.0.CO;2 [CrossRef]
  38. Pincivero DM, Gandaio CM, Ito Y. Gender-specific knee extensor torque, flexor torque, and muscle fatigue responses during maximal effort contractions. Eur J Appl Physiol. 2003;89:134–141. doi:10.1007/s00421-002-0739-5 [CrossRef]
  39. Billaut F, Bishop D. Muscle fatigue in males and females during multiple-sprint exercise. Sports Med. 2009;39:257–278. doi:10.2165/00007256-200939040-00001 [CrossRef]
  40. Lephart SM, Ferris CM, Riemann BL, Myers JB, Fu FH. Gender differences in strength and lower extremity kinematics during landing. Clin Orthop. 2002;(401):162–169.
  41. Pincivero DM, Campy RM, Coelho AJ. Knee flexor torque and perceived exertion: A gender and reliability analysis. Med Sci Sports Exerc. 2003;35:1720–1726. doi:10.1249/01.MSS.0000089246.90005.47 [CrossRef]
  42. Ahmad CS, Clark AM, Heilmann N, Schoeb JS, Gardner TR, Levine WN. Effect of gender and maturity on quadriceps-to-hamstring strength ratio and anterior cruciate ligament laxity. Am J Sports Med. 2006;34:370–374. doi:10.1177/0363546505280426 [CrossRef]
  43. Griffin JW, Tooms RE, Vanderzwaag R, Bertorini TE, O’Toole ML. Eccentric muscle performance of elbow and knee muscle groups in untrained men and women. Med Sci Sports Exerc. 1993;25:936–944.
  44. Hewett TE, Myer GD, Zazulak BT. Hamstrings to quadriceps peak torque ratios diverge between sexes with increasing isokinetic angular velocity. J Sci Med Sport. 2007;11:452–459. doi:10.1016/j.jsams.2007.04.009 [CrossRef]
  45. Hewett TE, Stroupe AL, Nance TA. Plyometric training in female athletes. Decreased impact forces and increased hamstring torques. Am J Sports Med. 1996;24:765–773. doi:10.1177/036354659602400611 [CrossRef]
  46. Castro MJ, McCann DJ, Shaffrath JD, Adams WC. Peak torque per unit cross-sectional area differs between strength-trained and untrained young-adults. Med Sci Sports Exerc. 1995;27:397–403.
  47. Emery CA. Does decreased muscle strength cause acute muscle strain injury in sport? A systematic review of the evidence. Phys Ther Rev. 1999;4:141–151.
  48. Foreman TK, Addy T, Baker S, Burns J, Hill N, Madden T. Prospective studies into the causation of hamstring injuries in sport: A systematic review. Phys Ther Sport. 2006;7:101–109. doi:10.1016/j.ptsp.2006.02.001 [CrossRef]
  49. Rampinini E, Coutts AJ, Castagna C, Sassi R, Impellizzeri FM. Variation in top level soccer match performance. Int J Sports Med. 2007;28:1018–1024. doi:10.1055/s-2007-965158 [CrossRef]
  50. Garrett WE Jr, Califf JC, Bassett FH 3rd, . Histochemical correlates of hamstring injuries. Am J Sports Med. 1984;12:98–103. doi:10.1177/036354658401200202 [CrossRef]
  51. Verrall GM, Slavotinek JP, Barnes PG. The effect of sports specific training on reducing the incidence of hamstring injuries in professional Australian rules of football players. Br J Sports Med. 2005;39:363–368. doi:10.1136/bjsm.2005.018697 [CrossRef]
  52. Orchard J. Biomechanics of muscle strain injury. NZ J Sport Med. 2002;30:90–96.
  53. Fuller CW, Ekstrand J, Junge A, et al. Consensus statement on injury definitions and data collection procedures in studies of football (soccer) injuries. Br J Sports Med. 2006;40:193–201. doi:10.1136/bjsm.2005.025270 [CrossRef]
  54. Dadebo B, White J, George KP. A survey of flexibility training protocols and hamstring strains in professional football clubs in England. Br J Sports Med. 2004;38:388–394. doi:10.1136/bjsm.2002.000044 [CrossRef]
  55. Verrall GM, Slavotinek JP, Barnes PG. The effect of sports specific training on reducing the incidence of hamstring injuries in professional Australian rules football players. Br J Sports Med. 2005;39:363–368. doi:10.1136/bjsm.2005.018697 [CrossRef]

Hamstring Strains and Estimated Adjusted Incidence Rate Ratios for Gender, National Collegiate Athletic Association Injury Surveillance System, 2004–2007 Athletic Seasons

GENDERHAMSTRING INJURIESATHLETE-EXPOSURESINCIDENCE RATE PER 1000 ATHLETE-EXPOSURESADJUSTED INJURY RATE RATIOa95% CONFIDENCE INTERVAL
Female2991,387,2500.2161.00
Male12772,658,9380.4801.621.28–2.05

Hamstring Strains with Associated Incidence Rate Ratios for Sport Among Men and Women, National Collegiate Athletic Association Injury Surveillance System, 2004–2007 Athletic Seasons

GENDERHAMSTRING INJURIESATHLETE-EXPOSURESINCIDENCE RATE PER 1000 ATHLETE-EXPOSURESADJUSTED INJURY RATE RATIOa95% CONFIDENCE INTERVAL
Men
  Soccer194280,8110.6911.00
  Football8071,336,1980.6040.860.74–1.01
  Lacrosse58128,8340.4500.640.48–0.86
  Baseball130359,6970.3610.520.42–0.65
  Basketball71385,0700.1840.270.20–0.35
  Wrestling14111,9150.1250.180.10–0.31
  Tennis218,4000.1090.150.04–0.62
  Cross country138,0130.0260.040.01–0.27
Women
  Soccer117306,9920.3811.00
  Field hockey3284,4640.3790.990.60–1.62
  Lacrosse21114,5300.1830.490.27–0.88
  Basketball58347,1220.1670.440.30–0.66
  Softball402447060.1640.430.28–0.68
  Tennis323,6360.1270.350.08–1.48
  Cross country542,0400.1190.320.10–1.00
  Volleyball23223,7600.1030.270.15–0.48
Authors

Mr Cross is from the University of Virginia, Sports Medicine Program; Drs Gurka and Conaway are from the University of Virginia School of Medicine, Charlottesville, Va. Dr Ingersoll is from the The Herbert H. and Grace A. Dow College of Health Professions, Central Michigan University, Mount Pleasant, Mich.

The authors have no financial or proprietary interest in the materials presented herein.

Address correspondence to Kevin Cross, MS, ATC, PT, 5004 Madison Court, Charlottesville, VA 22911; e-mail: .kmc7e@virginia.edu

10.3928/19425864-20100428-06

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