Male professional rugby players with hamstring/quadriceps muscle imbalance have an increased risk of hamstring injuries during the season

Male professional rugby players with hamstring/quadriceps muscle imbalance have an increased risk of hamstring injuries during the season | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Male professional rugby players with hamstring/quadriceps muscle imbalance have an increased risk of hamstring injuries during the season Maxime Grolier, Mathilde Pelletier- Visa, Marc Julia, Dominique Morand, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6445849/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 6 You are reading this latest preprint version Abstract Background: Hamstring injuries (HI) are among the most common muscle injuries in team ball sports. Hamstring strenght deficit is an intrinsic risk factor for HI. To evaluate the rate of occurrence of HI in male professional rugby “Top 14” players during one season and to study the possible relationships among hamstring strength deficit (evaluated by isokinetic dynamometry), muscle extensibility defects, field position and the risk of HI. Study Design: Descriptive epidemiology study. Methods: The rate of HI was prospectively studied in 134 professional rugby players from four French professional teams over one competitive season. Preseason isokinetic and muscle extensibility tests were performed. The recorded information included the field position and history of injuries. The analysis was performed by comparing two groups: without (Group A) and with (Group B) preseason isokinetic imbalance. Results: During the season, the rate of HI was 29.9% (95% CI: 22.2-38.4%), with fewer injuries in Group A than in Group B (21.0%, 95% CI: 11.6-33.2% versus 37.5%, 95% CI: 26.3-49.7%, respectively). According to the multivariable analysis, Group B had an increased risk of HI compared with Group A (OR: 2.65, 95% CI: 1.08-6.44, p=0.032 ), as did the players with a history of HI (OR: 2.96, 95% CI: 1.06-8.28, p=0.039 ), whereas the players’ field position was not significantly associated with HI. Conclusion: The rate of HI among professional rugby players is high. An isokinetic imbalance in the preseason is a risk factor for injury during the season. This knowledge can be used to implement prevention strategies in professional sports. Clinical trial number : Not applicable Epidemiology injury prevention isokinetic muscle injury rugby Figures Figure 1 INTRODUCTION Hamstring (H) injuries are among the most common muscle injuries in team ball sports, such as football 1 – 3 , Australian football 4 , 5 , American football 6 and rugby 7 – 9 . In professional football, Australian football and rugby, this type of injury accounts for approximately 11–16% of all injuries and approximately one-third of muscle injuries 10 – 12 . The recurrence rate is between 13% and 23%, depending on the series 8 , 10 – 12 . The risk factors for H injury can be separated into extrinsic factors (related to sport activity modalities) and intrinsic factors (related to athletes’ individual features) by isolating the history of H injury 13 . Intrinsic factors include muscle stiffness 14 and H muscle strength deficit 13 . Isokinetic testing is currently considered the gold standard for measuring dynamic thigh muscle strength [H and quadriceps (Q)] 15 , 16 . These tests can provide valuable information for designing effective preventive strategies for athletes. In a prospective study involving a sample of 462 professional football players, Croisier et al. reported that the rate of H injury was significantly greater in subjects with untreated muscle strength imbalances than in players with no imbalances in the preseason (relative risk: 4.66, 95% confidence interval (95% CI): 2.01–10.80) and that normalization of isokinetic parameters reduced the risk factor for injury to that observed in players with no imbalances (relative risk: 1.43, 95% CI: 0.44–4.71) 17 . Isokinetic testing is already used in routine practice by many professional rugby clubs during systematic preseason assessment for injury prevention or rehabilitation purposes. The measurement of dynamic muscle strength is now possible in an accurate and reproducible way because of the use of isokinetic devices 18 . The application of this technique and its reproducibility for the knee joint have been widely validated in the literature 16 , 19 – 23 . Data on the isokinetic assessment of French professional rugby players have recently been published 24 . These data are all more important, as rugby has many similarities with football in terms of biomechanical and energetic demands, although there are differences in size and running speed 25 depending on the field position. Other risk factors include a history of H injury, which is frequently recognized as a risk factor for reinjury 13 , 26 , 27 . This risk factor may be associated with a muscle strength deficit 28 but may also be an independent factor (fibrous scarring) 26 . Given the frequency of these injuries and the impact on sports performance associated with a high risk of recurrence, it is natural to consider secondary prevention actions by assessing H extensibility and screening for muscle strength deficits via isokinetics. These actions can also be applied from a tertiary prevention perspective to reduce the risk of recurrence. To our knowledge, no published study has evaluated the predictive effect of isokinetic muscle strength and extensibility measurements on the risk of H injury in professional rugby players. Thus, the identification of such an effect would allow the implementation of preventive management for these muscle injuries. Main objective The main objective of this study was to evaluate the rate of H injuries in male professional rugby players during one season in a prospective study. Secondary objectives The secondary objectives were to study the possible relationships between H strength deficit and/or muscle extensibility defects and/or field position and the risk of H injury in a sample of professional rugby players. Similarly, the relationships between muscle injury and muscle strength parameters (assessed with an isokinetic device) during the preseason, on the one hand, and the presence of a previous injury, on the other hand, were studied. The associations of these elements with the occurrence of H injury were evaluated as has been done in other samples 17 . METHODS Study design A prospective study (cohort) for 12 months aimed to evaluate the rate of H injuries in male professional rugby players. The study started at the end of the 2010–2011 sports season, with monthly follow-up until the end of the 2011–2012 season. The isokinetic evaluation took place during the off-season (during the last two weeks of the 2010/2011 season or during the first three weeks of the 2011/2012 season). This manuscript was prepared in accordance with the STROBE guidelines 29 for reporting observational studies and the author guidelines of BMC Sports Science, Medicine and Rehabilitation Practical conduct of the study for the players At the inclusion visit, the volunteers at each professional club participating in the study provided their nonopposition after receiving detailed information. The following data were then collected: field position, weight, height, and medical and surgical history. The players were then assessed for muscle extensibility before any warm-up. They then warmed on a cycle ergometer for 10 minutes and performed a maximal isokinetic test for both thighs. During the 12-month prospective follow-up, each local manager was asked to identify new thigh muscle injuries by completing a specific questionnaire. The questionnaire used was developed solely for this study ( supplementary file ). Data were anonymized throughout the protocol. The investigators processing the data therefore only had access to this anonymized information. To ensure the completeness of the collection of injuries, each local manager was contacted monthly. Participants The medical staff of 14 “Top 14” clubs (2011–2012 season) were asked to participate in this study. The players included in this study were volunteers and did not receive any compensation, especially since the isokinetic assessment, muscle extensibility and injury history were part of the systematic preseason medical check-up of these clubs. The players included in this study had to meet the following criteria: be of legal age, be professional rugby players, be physically fit to perform H and Q muscle tests, have received information and have signed a letter of nonopposition. The exclusion criteria were recent Q or H muscle injury, recent knee joint injury, and a player who stopped playing rugby. An injury is no longer considered to be recent once the player has been able to return to opposition training or matches for at least two weeks. The investigator could intervene to interrupt the tests if he judged that the player’s state of health did not allow him to continue the protocol. For any premature exit from the study, the date and reason were indicated on the player’s follow-up sheet. Patient and public involvement Patients were not included in this study. Variables The primary outcome was the rate of hamstring injury (prospective collection over 12 months), which was defined by clinical examination and the inability to compete for more than two weeks. The secondary outcome included preseason parameters such as muscle strength parameters (assessed by isokinetics), muscle extensibility parameters, history of hamstring injury, body mass index (BMI) and player field position. The players were grouped according to running speed profiles 25 . Assessment of muscle strength Assessments were performed via a motorized computerized dynamometer of the Con-Trex® or Cybex Norm® type. The protocol modalities were inspired by the study of Croisier et al. 17 . The measurements were preceded by a warm-up consisting of pedaling on an ergometric bicycle at 1 watt/kg. Seated on the dynamometer (with 85° of coxofemoral flexion), the body was stabilized by several straps around the thigh, waist, and chest to avoid compensation. The gravitational factor of the dynamometer’s lever arm and lower leg-segment ensemble was compensated for during the measurements. Adequate familiarity with the dynamometer was provided in the form of additional warm-up isokinetic repetitions in concentric mode at an angular speed of 120 deg/s. The testing protocol included concentric exertions of both the hamstring and quadriceps muscle groups at angular speeds of 60 deg/s (3 repetitions) and 240 deg/s (5 repetitions). Then, the hamstrings were subjected to eccentric angular speeds of 30 deg/s (3 repetitions). All sets of tests were separated by one minute of rest. Before assessment, three preliminary submaximal repetitions routinely preceded each test speed. Oral encouragement was given. In the absence of a consensus, two groups of players were defined after isokinetic strength assessment. Group A was composed of players who did not show any imbalance in the isokinetic assessment, and Group B was composed of players with any kind of imbalance: Bilateral H asymmetry was defined as a difference in muscle strength > 15% between the right and left sides, either on concentric 60 deg/s or eccentric 30 deg/s analysis 17 . The standard ratio between H and Q was considered abnormal if it was less than 0.47 or 0.45 for Cybex or Contrex, respectively, in the concentric or eccentric analysis. Similarly, the mixed ratio was considered abnormal if the H/Q ratio was less than 0.8 or 0.89 for Cybex or Contrex, respectively. The combination of these two imbalances. Statistical analysis The sample size was estimated to guarantee satisfactory accuracy of the primary endpoint. With four clubs, approximately 120–150 professional rugby players could be expected. Therefore, for a H injury rate close to 15%, the 95% CI had an accuracy of 5%. Statistical analysis was performed via Stata software (version 15; StataCorp, College Station, Texas, USA). All tests were two-sided, with an alpha level set at 5%. Categorical data are expressed as the number of players and percentages, and continuous data are expressed as the mean ± standard deviation or median [25th ; 75th percentiles], according to their statistical distribution. Comparisons between groups A and B were carried out via the following statistical tests: the chi-square test or Fisher’s exact test for categorical variables and Student’s t test or the Mann‒Whitney test for quantitative variables. The rate of H injuries was presented with a 95% CI estimated by a binomial distribution. The factors associated with H injuries were studied via generalized linear mixed models (with a logit link function) to consider a cluster (club) effect. The results are expressed as odds ratios (ORs) and 95% CIs. Finally, a multivariable analysis was performed with the same statistical model, with covariates determined according to univariate results and clinical relevance (groups A and B, field position and history of H injury) 30 . Equity, diversity and inclusion statement The study population is made up entirely of male players, as rugby is not a mixed sport at the professional level. The research team is mixed. Race/ethnicity/culture was not assessed, but French rugby clubs are known to be plural. No discrimination was made during recruitment, as almost all players from the participating clubs were included. RESULTS Participants A total of 134 professional rugby players from four “top 14” clubs were included in this study (Fig. 1 ). Group A (no muscle strength imbalance) consisted of 62 players, whereas Group B (the presence of an imbalance) consisted of 72 players. In this sample, 23.9% of the players had a previous history of H injury, 30.6% in Group A versus 18.1% in Group B. There was no significant difference between the two groups in terms of BMI, distribution of field positions, previous injury or extensibility parameters ( Table 1 ). Table 1 Characteristics of the participants at baseline (n = 134). Total (n = 134) Group A (n = 62) Group B (n = 72) p Body mass index (kg/m 2 ) 29.6 ± 3.5 29.6 ± 3.0 29.6 ± 3.8 0.95 Field position (by number) 0.69 1–5 61 (45.5) 30 (48.4) 31 (43.0) 6–8 19 (14.2) 9 (14.5) 10 (13.9) 9–10 17 (12.7) 8 (12.9) 9 (12.5) 11–12 20 (14.9) 10 (16.1) 10 (13.9) 13–15 17 (12.7) 5 (8.1) 12 (16.7) History of hamstring injury 32 (23.9) 19 (30.6) 13 (18.1) 0.088 Extensibility of thigh muscles Right hamstring (degrees) 82.9 ± 10.3 82.3 ± 11.0 83.4 ± 9.6 0.52 Left hamstring (degrees) 81.6 ± 10.3 81.4 ± 11.3 81.7 ± 9.4 0.85 Right quadriceps (cm) 8 [0; 12] 6 [2; 12] 9 [0; 13] 0.60 Left quadriceps (cm) 8 [0; 13] 6 [2; 13] 9 [0; 13] 0.71 Data are presented as number of players (percentages in columns), mean ± standard deviation or median [25th ; 75th percentiles]. Group A: players without muscle strength imbalance; Group B: players with muscle strength imbalance. Analysis of the primary endpoint During the season, the rate of H injuries was 29.9% (95% CI: 22.2–38.4%), with fewer injuries in Group A than in Group B (21.0%, 95% CI: 11.6–33.2% versus 37.5%, 95% CI: 26.3–49.7%, respectively). Analysis of secondary endpoints Factors associated with H injury during the 12-month follow-up of the players are presented in Table 2 . Players with a history of H injury had an increased risk of H injury during the season (OR: 2.65, 95% CI: 1.03–6.81, p = 0.043). Table 2 Factors associated with hamstring injury after 12 months of prospective follow-up (univariate analysis). No injury Injury OR [95%CI] p Group A (n = 62) 49 (79.0) 13 (21.0) Ref. B (n = 72) 45 (62.5) 27 (37.5) 2.12 [0.93; 4.83] 0.073 Body mass index (kg/m 2 ) 29.3 ± 3.1 30.1 ± 4.2 1.06 [0.94; 1.18] 0.33 Field position (by number) 1–5 (n = 61) 43 (70.5) 18 (29.5) Ref. 6–8 (n = 19) 13 (68.4) 6 (31.6) 1.27 [0.38; 4.20] 0.69 9–10 (n = 17) 14 (82.4) 3 (17.6) 0.60 [0.14; 2.51] 0.48 11–12 (n = 20) 12 (60.0) 8 (40.0) 1.85 [0.59; 5.77] 0.29 13–15 (n = 17) 12 (70.6) 5 (29.4) 1.17 [0.11; 0.83] 0.81 Hamstring injury history No (n = 102) 75 (73.5) 27 (26.5) Ref. Yes (n = 32) 19 (59.4) 13 (40.6) 2.65 [1.03; 6.81] 0.043 Extensibility of thigh muscles Right hamstring (degrees) 83.2 ± 10.4 82.1 ± 10.0 0.98 [0.94; 1.02] 0.36 Left hamstring (degrees) 81.9 ± 10.2 80.7 ± 10.7 0.99 [0.95; 1.03] 0.54 Right quadriceps (cm) 5 [0; 12] 11 [7; 15] 1.08 [0.98; 1.17] 0.10 Left quadriceps (cm) 6 [0; 12] 11 [6; 15] 1.07 [0.98; 1.16] 0.092 Data are presented as number of players (percentages in rows), mean ± standard deviation or median [25th ; 75th percentiles]. CI: confidence interval; Group A: players without muscle strength imbalance; Group B: players with muscle strength imbalance; OR: odds ratio; Ref: reference. According to the multivariable analysis (Table 3 ), players in Group B had an increased risk of H injury compared with players in Group A (OR: 2.65, 95% CI: 1.08–6.44, p = 0.032), as did players with H injury history (OR: 2.96, 95% CI: 1.06–8.28, p = 0.039), whereas players’ field position was not significantly associated with H injury. Table 3 Factors associated with hamstring injury after 12 months of prospective follow-up (multivariable analysis). OR [95%CI] p Group A (n = 62) Ref. B (n = 72) 2.65 [1.08; 6.44] 0.032 Hamstring injury history No (n = 102) Ref. Yes (n = 32) 2.96 [1.06; 8.28] 0.039 Field position (by number) 1–5 (n = 61) Ref. 6–8 (n = 19) 1.17 [0.34; 3.97] 0.80 9–10 (n = 17) 0.61 [0.13; 2.65] 0.51 11–12 (n = 20) 1.42 [0.42; 4.77] 0.57 13–15 (n = 17) 0.81 [0.20; 3.19] 0.76 CI: confidence interval; Group A: players without muscle strength imbalance; Group B: players with muscle strength imbalance; OR: odds ratio; Ref: reference. The rate of H injury during the season increased significantly according to the group and history of H injury: 20.9% (9/43) in Group A players without a history of H injury, 21.1% (4/19) in Group A players with a history of H injury, 30.5% (18/59) in Group B players without a history of H injury, and 69.2% (9/13) in Group B players with a history of H injury (p = 0.014). DISCUSSION In recent years, there has been a particular interest in the prevention of muscle injuries in sports, especially in H, which explains the abundance of scientific work on this subject in the literature 2 , 31 – 35 . Although this risk of injury is multifactorial in origin, the presence of a lower limb muscle strength imbalance nevertheless plays a fundamental role. The main objective of this study was to assess the rate of H injuries in a sample of “Top 14” professional rugby players over the course of a sporting season. The rate of H injuries was 29.9% (95% CI: 22.2–38.4%), which is higher than the expected results (13–23%) and the data in the literature 8 , 10 – 12 . As the power developed during repeated thrusting efforts or during tackling in rugby is greater than that developed in football, it may seem legitimate to observe a greater rate of injury in this sport. In parallel, the higher the training load is, the greater the risk of injury. Other studies on the occurrence of injury in this sport have widely recognized that as the intensity, duration and load of a training session or match increases, so does the incidence of injury 36 , 37 . Furthermore, many studies on the incidence of injuries have been carried out on relatively heterogeneous samples, including professionals, semiprofessionals and even amateurs, which is not the case in our study, where all the players belong to a “Top 14” club. Players with a muscular imbalance (either a bilateral asymmetry of the H or an anterior‒posterior imbalance in the H/Q pair) at the start of the season had an increased risk of H injury compared with players without an imbalance (OR: 2.65, 95% CI: 1.08–6.44, p = 0.032), regardless of injury history and field position. The rate of H injuries remains higher than expected. This variability could be explained by the greater or lesser proportion of players with a muscular imbalance at the start of the season, who are at risk of injury that is twice as high during the season. Particular attention should therefore be paid to this category of players during the season. Furthermore, players with a history of H injury had a high risk of injury (OR: 2.96, 95% CI: 1.06–8.28, p = 0.039), which is consistent with the literature 13 , 27 . We have also shown that, in this sample of professional rugby players, this excess risk is independent of preseason isokinetic assessment and field position. Concerning the lack of extensibility of thigh muscles, the presence of H or Q retraction was not associated with an increased risk of injury in our study. Witvrouw et al. reported that H and Q tightness was a risk factor for injury to these muscle groups 14 . To our knowledge, no other study has examined this association under similar conditions, i.e., with a prospective study over 12 months, thus limiting the comparison of our results with the literature. Analysis according to the players’ field position reveals that there is no position more at risk of muscle injuries. Nevertheless, the question of which field position is most exposed remains open. Limitations We can mention some incomplete collection of data by the clubs, which can be explained, on the one hand, by the difficulties encountered in collecting the data (regular reminders to the club physicians) and, on the other hand, by the permanent flow of arrivals and departures of players at this time of the sports season. In addition, there is a potential measurement bias because not all clubs had the same isokinetic dynamometer for measuring muscle strength and because the measurement was carried out by different physicians. Of the four clubs that met the requirements, two had a Cybex dynamometer, and two had a Contrex dynamometer. To limit this bias, we used thresholds specific to each dynamometer to establish the normality of the muscle strength ratios on the basis of the work of Croisier et al. 17 . H muscle injury was defined by clinical examination and by being unfit for competition for more than two weeks. However, the stage of the injury and the exact duration of unavailability were not reported for each injury, which would have allowed for a more refined interpretation of these results. Furthermore, it would have been relevant to collect the training and match time of the players to relate our results to a physical load (risk of injury per minute of training/match). The type of pitch on which the injury occurred was not taken into account. We know that the risk of injury also varies according to the type of pitch. Among synthetic turf, this risk also varies because the new materials used in the latest generation of synthetic turf allow for greater shock absorption. These are characterized by longer fibers and synthetic rubber elements, which reduce the frictional forces and the stiffness of the ground. Finally, it would have been interesting to integrate additional epidemiological data (e.g., the ethnic origin of players) as well as the distribution of these injuries throughout the season, which would allow a more precise analysis of the circumstances of the occurrence of these injuries. The impact of a busy schedule is still being debated. The idea is to implement preventive measures at the right moment in the season. We know that this incidence usually tends to increase progressively during the season, especially for clubs taking part in numerous competitions, as was the case for this sample of players (championship, cups, etc.) 36 – 38 . CONCLUSION These results show that the rate of H injuries in professional rugby is high. An imbalance in the isokinetic balance in the preseason is a risk factor for the occurrence of an injury during the season. This knowledge can be used to implement prevention strategies in professional sports. Abbreviations BMI: body mass index CI: confidence interval H: hamstring OR: odds ratio Q: quadriceps Declarations Ethical approval information This study was conducted at the Clermont-Ferrand University Hospital. All procedures concerning the participants were carried out in accordance with the ethical standards of the Interregional Ethics Committee. A favorable ethical opinion was delivered by the inter-regional ethics committee “ Comité d’Ethique des Centres d’Investigation Clinique de l’inter-région Rhône-Alpes –Auvergne ” whose file number is: CE-CIC-GREN-11/23 obtained in January 2012. In accordance with current regulations and the principles outlined in the Declaration of Helsinki, all participants were informed in a clear, comprehensible, and appropriate manner about the objectives, procedures, potential benefits, and possible risks associated with their participation in the study. Participation was voluntary, and a non-objection form was completed in cases where individuals declined to take part. No identifying patient data are included in this manuscript. Consent for publication Not applicable. Availability of data and materials The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request. Competing interests: No potential conflicts of interest declared. Funding: None Authors’ contributions The guarantor is the name of the corresponding author; whose initials are MG. The conception and design of the study was made by EC, MJ and DM. The drafting of the original protocol by EC, MJ, DM and CL. The coordination of the study by EC. The acquisition of data by MG. The design of the statistical analysis plan by BP and CL. The drafting of the present manuscript by MG, MPV and EC. The final approval by all authors. References Ekstrand J, Hagglund M, Walden M. 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Hamstring muscle strain recurrence and strength performance disorders. Am J Sports Med . 2002;30(2):199-203. doi:10.1177/03635465020300020901 von Elm E, Altman DG, Egger M, Pocock SJ, Gøtzsche PC, Vandenbroucke JP. Strengthening the reporting of observational studies in epidemiology (STROBE) statement: guidelines for reporting observational studies. BMJ . 2007;335(7624):806-808. doi:10.1136/bmj.39335.541782.AD Mansournia MA, Collins GS, Nielsen RO, et al. A CHecklist for statistical Assessment of Medical Papers (the CHAMP statement): explanation and elaboration. Br J Sports Med . 2021;55(18):1009-1017. doi:10.1136/bjsports-2020-103652 Arnason A, Sigurdsson SB, Gudmundsson A, Holme I, Engebretsen L, Bahr R. Risk Factors for Injuries in Football. Am J Sports Med . 2004;32(1_suppl):5-16. doi:10.1177/0363546503258912 Dvorak J, Junge A. Football Injuries and Physical Symptoms. Am J Sports Med . 2000;28(5_suppl):3-9. doi:10.1177/28.suppl_5.s-3 Dvorak J, Junge A, Chomiak J, et al. Risk factor analysis for injuries in football players. Possibilities for a prevention program. Am J Sports Med . 2000;28(5 Suppl):S69-74. doi:10.1177/28.suppl_5.s-69 Engebretsen L, Bahr R. An ounce of prevention? Br J Sports Med . 2005;39(6):312-313. doi:10.1136/bjsm.2005.018333 Junge A, Dvorak J. Soccer injuries: a review on incidence and prevention. Sports Med Auckl NZ . 2004;34(13):929-938. doi:10.2165/00007256-200434130-00004 Gabbett TJ. Influence of training and match intensity on injuries in rugby league. J Sports Sci . 2004;22(5):409-417. doi:10.1080/02640410310001641638 Gabbett T, Hodgson P. Incidence of injury in semi-professional rugby league players. Br J Sports Med . 2003;37(1):36-44. doi:10.1136/bjsm.37.1.36 Gabbett T. Incidence, site, and nature of injuries in amateur rugby league over three consecutive seasons. Br J Sports Med . 2000;34(2):98-103. doi:10.1136/bjsm.34.2.98 Additional Declarations No competing interests reported. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6445849","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":458544148,"identity":"b6371392-202d-47ba-a613-9ca8cbff9e89","order_by":0,"name":"Maxime Grolier","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABJElEQVRIie2PMUvDQBTHXxE6BbI+iegnEF4IpCmEfpYngXMJreDiUDCTHd0kg1/B1flK4FxSXAOCRBxcOmTsYKnXxoI0qTg63A+Oe/zv/Xj3AAyG/0pJADZY6zL4jsL6wm2xC2vlMLHqng1SbBWxR9GH5F+V09uHt5IvwpH3NFMIYzzu3WXqveJw1JvMpgXw667iFx8eMYn+Yz4UCAq9oxdxTpJF/z4fRgHwZVNRXWTKyC8s31kmeJY6sY/TRUYIuugseI+yIi+1dEOC1xtF8orQnvsI3FSeb9aKJMJaYawVSYhxu1J0D/QuEWEee4HexU0dITBnneDcC7htiuqU1eeA7EnuFjAOT9CJFF7xQH8sdouqqQA2o5+0vdryV8VgMBgMAF+s2mUCu83MlQAAAABJRU5ErkJggg==","orcid":"","institution":"Centre Hospitalier Universitaire de Clermont-Ferrand","correspondingAuthor":true,"prefix":"","firstName":"Maxime","middleName":"","lastName":"Grolier","suffix":""},{"id":458544149,"identity":"0dca0397-1e40-4c46-83dd-af4bb795ca99","order_by":1,"name":"Mathilde Pelletier- Visa","email":"","orcid":"","institution":"Centre Hospitalier Universitaire de Clermont-Ferrand","correspondingAuthor":false,"prefix":"","firstName":"Mathilde","middleName":"Pelletier-","lastName":"Visa","suffix":""},{"id":458544150,"identity":"6f2674f5-3f20-4007-aaeb-ba1d4a3318f2","order_by":2,"name":"Marc Julia","email":"","orcid":"","institution":"CHRU Montpellier","correspondingAuthor":false,"prefix":"","firstName":"Marc","middleName":"","lastName":"Julia","suffix":""},{"id":458544151,"identity":"4bb31437-25e7-46d2-a165-c8ebe13da51c","order_by":3,"name":"Dominique Morand","email":"","orcid":"","institution":"Centre Hospitalier Universitaire de Clermont-Ferrand","correspondingAuthor":false,"prefix":"","firstName":"Dominique","middleName":"","lastName":"Morand","suffix":""},{"id":458544152,"identity":"b104237c-4be7-4e0d-a1a8-7316efac716f","order_by":4,"name":"Bruno Pereira","email":"","orcid":"","institution":"Centre Hospitalier Universitaire de Clermont-Ferrand","correspondingAuthor":false,"prefix":"","firstName":"Bruno","middleName":"","lastName":"Pereira","suffix":""},{"id":458544153,"identity":"6429f5b2-3720-4120-aee6-09cf0b234dbb","order_by":5,"name":"Céline Lambert MSc","email":"","orcid":"","institution":"Centre Hospitalier Universitaire de Clermont-Ferrand","correspondingAuthor":false,"prefix":"","firstName":"Céline","middleName":"Lambert","lastName":"MSc","suffix":""},{"id":458544154,"identity":"29c1f599-3f4d-4704-92ff-acb711ccebd9","order_by":6,"name":"Emmanuel Coudeyre","email":"","orcid":"","institution":"Centre Hospitalier Universitaire de Clermont-Ferrand","correspondingAuthor":false,"prefix":"","firstName":"Emmanuel","middleName":"","lastName":"Coudeyre","suffix":""}],"badges":[],"createdAt":"2025-04-14 12:08:20","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6445849/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6445849/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":83141124,"identity":"fe62dbec-4cb1-4bdc-9cde-a2d2a59dd941","added_by":"auto","created_at":"2025-05-20 12:16:43","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":106067,"visible":true,"origin":"","legend":"\u003cp\u003eFlowchart of the study.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eData are presented as number of teams (N) and number of players (n). H: hamstring; Q: quadriceps.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6445849/v1/5d2c5469282221eb8a5e5343.jpeg"},{"id":83143835,"identity":"fd0642dd-2e9c-4234-847e-134a492aebd1","added_by":"auto","created_at":"2025-05-20 12:40:43","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1045398,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6445849/v1/aa6b9aed-acb7-44cc-a772-fc4f31902327.pdf"},{"id":83141125,"identity":"efb8bcb6-8174-453e-a6ca-f17118a3facc","added_by":"auto","created_at":"2025-05-20 12:16:43","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":29857,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementaryfilequestionnaires.docx","url":"https://assets-eu.researchsquare.com/files/rs-6445849/v1/cd902be8c1c436f57479cf5b.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Male professional rugby players with hamstring/quadriceps muscle imbalance have an increased risk of hamstring injuries during the season","fulltext":[{"header":"INTRODUCTION","content":"\u003cp\u003eHamstring (H) injuries are among the most common muscle injuries in team ball sports, such as football \u003csup\u003e\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e, Australian football\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e,\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e, American football \u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e and rugby\u003csup\u003e\u003cspan additionalcitationids=\"CR8\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. In professional football, Australian football and rugby, this type of injury accounts for approximately 11\u0026ndash;16% of all injuries and approximately one-third of muscle injuries\u003csup\u003e\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. The recurrence rate is between 13% and 23%, depending on the series\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. The risk factors for H injury can be separated into extrinsic factors (related to sport activity modalities) and intrinsic factors (related to athletes\u0026rsquo; individual features) by isolating the history of H injury\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. Intrinsic factors include muscle stiffness \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e and H muscle strength deficit\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIsokinetic testing is currently considered the gold standard for measuring dynamic thigh muscle strength [H and quadriceps (Q)]\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. These tests can provide valuable information for designing effective preventive strategies for athletes. In a prospective study involving a sample of 462 professional football players, Croisier et al. reported that the rate of H injury was significantly greater in subjects with untreated muscle strength imbalances than in players with no imbalances in the preseason (relative risk: 4.66, 95% confidence interval (95% CI): 2.01\u0026ndash;10.80) and that normalization of isokinetic parameters reduced the risk factor for injury to that observed in players with no imbalances (relative risk: 1.43, 95% CI: 0.44\u0026ndash;4.71)\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. Isokinetic testing is already used in routine practice by many professional rugby clubs during systematic preseason assessment for injury prevention or rehabilitation purposes. The measurement of dynamic muscle strength is now possible in an accurate and reproducible way because of the use of isokinetic devices\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. The application of this technique and its reproducibility for the knee joint have been widely validated in the literature\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan additionalcitationids=\"CR20 CR21 CR22\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e. Data on the isokinetic assessment of French professional rugby players have recently been published\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. These data are all more important, as rugby has many similarities with football in terms of biomechanical and energetic demands, although there are differences in size and running speed \u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e depending on the field position.\u003c/p\u003e \u003cp\u003eOther risk factors include a history of H injury, which is frequently recognized as a risk factor for reinjury\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e,\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. This risk factor may be associated with a muscle strength deficit \u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e but may also be an independent factor (fibrous scarring)\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eGiven the frequency of these injuries and the impact on sports performance associated with a high risk of recurrence, it is natural to consider secondary prevention actions by assessing H extensibility and screening for muscle strength deficits via isokinetics. These actions can also be applied from a tertiary prevention perspective to reduce the risk of recurrence.\u003c/p\u003e \u003cp\u003eTo our knowledge, no published study has evaluated the predictive effect of isokinetic muscle strength and extensibility measurements on the risk of H injury in professional rugby players. Thus, the identification of such an effect would allow the implementation of preventive management for these muscle injuries.\u003c/p\u003e\n\u003ch3\u003eMain objective\u003c/h3\u003e\n\u003cp\u003eThe main objective of this study was to evaluate the rate of H injuries in male professional rugby players during one season in a prospective study.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eSecondary objectives\u003c/h2\u003e \u003cp\u003eThe secondary objectives were to study the possible relationships between H strength deficit and/or muscle extensibility defects and/or field position and the risk of H injury in a sample of professional rugby players. Similarly, the relationships between muscle injury and muscle strength parameters (assessed with an isokinetic device) during the preseason, on the one hand, and the presence of a previous injury, on the other hand, were studied. The associations of these elements with the occurrence of H injury were evaluated as has been done in other samples\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e"},{"header":"METHODS","content":"\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eStudy design\u003c/h2\u003e \u003cp\u003eA prospective study (cohort) for 12 months aimed to evaluate the rate of H injuries in male professional rugby players. The study started at the end of the 2010\u0026ndash;2011 sports season, with monthly follow-up until the end of the 2011\u0026ndash;2012 season. The isokinetic evaluation took place during the off-season (during the last two weeks of the 2010/2011 season or during the first three weeks of the 2011/2012 season). This manuscript was prepared in accordance with the STROBE guidelines\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e for reporting observational studies and the author guidelines of BMC Sports Science, Medicine and Rehabilitation\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003ePractical conduct of the study for the players\u003c/h3\u003e\n\u003cp\u003eAt the inclusion visit, the volunteers at each professional club participating in the study provided their nonopposition after receiving detailed information. The following data were then collected: field position, weight, height, and medical and surgical history. The players were then assessed for muscle extensibility before any warm-up. They then warmed on a cycle ergometer for 10 minutes and performed a maximal isokinetic test for both thighs. During the 12-month prospective follow-up, each local manager was asked to identify new thigh muscle injuries by completing a specific questionnaire. The questionnaire used was developed solely for this study (\u003cspan type=\"BoldItalicUnderline\" class=\"BoldItalicUnderline\" name=\"Emphasis\"\u003esupplementary file\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eData were anonymized throughout the protocol. The investigators processing the data therefore only had access to this anonymized information. To ensure the completeness of the collection of injuries, each local manager was contacted monthly.\u003c/p\u003e\n\u003ch3\u003eParticipants\u003c/h3\u003e\n\u003cp\u003eThe medical staff of 14 \u0026ldquo;Top 14\u0026rdquo; clubs (2011\u0026ndash;2012 season) were asked to participate in this study. The players included in this study were volunteers and did not receive any compensation, especially since the isokinetic assessment, muscle extensibility and injury history were part of the systematic preseason medical check-up of these clubs. The players included in this study had to meet the following criteria: be of legal age, be professional rugby players, be physically fit to perform H and Q muscle tests, have received information and have signed a letter of nonopposition. The exclusion criteria were recent Q or H muscle injury, recent knee joint injury, and a player who stopped playing rugby. An injury is no longer considered to be recent once the player has been able to return to opposition training or matches for at least two weeks.\u003c/p\u003e \u003cp\u003eThe investigator could intervene to interrupt the tests if he judged that the player\u0026rsquo;s state of health did not allow him to continue the protocol. For any premature exit from the study, the date and reason were indicated on the player\u0026rsquo;s follow-up sheet.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003ePatient and public involvement\u003c/h2\u003e \u003cp\u003ePatients were not included in this study.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eVariables\u003c/h3\u003e\n\u003cp\u003eThe primary outcome was the rate of hamstring injury (prospective collection over 12 months), which was defined by clinical examination and the inability to compete for more than two weeks.\u003c/p\u003e \u003cp\u003eThe secondary outcome included preseason parameters such as muscle strength parameters (assessed by isokinetics), muscle extensibility parameters, history of hamstring injury, body mass index (BMI) and player field position. The players were grouped according to running speed profiles\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\n\u003ch3\u003eAssessment of muscle strength\u003c/h3\u003e\n\u003cp\u003eAssessments were performed via a motorized computerized dynamometer of the Con-Trex\u0026reg; or Cybex Norm\u0026reg; type. The protocol modalities were inspired by the study of Croisier et al.\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. The measurements were preceded by a warm-up consisting of pedaling on an ergometric bicycle at 1 watt/kg. Seated on the dynamometer (with 85\u0026deg; of coxofemoral flexion), the body was stabilized by several straps around the thigh, waist, and chest to avoid compensation. The gravitational factor of the dynamometer\u0026rsquo;s lever arm and lower leg-segment ensemble was compensated for during the measurements. Adequate familiarity with the dynamometer was provided in the form of additional warm-up isokinetic repetitions in concentric mode at an angular speed of 120 deg/s. The testing protocol included concentric exertions of both the hamstring and quadriceps muscle groups at angular speeds of 60 deg/s (3 repetitions) and 240 deg/s (5 repetitions). Then, the hamstrings were subjected to eccentric angular speeds of 30 deg/s (3 repetitions). All sets of tests were separated by one minute of rest. Before assessment, three preliminary submaximal repetitions routinely preceded each test speed. Oral encouragement was given.\u003c/p\u003e \u003cp\u003eIn the absence of a consensus, two groups of players were defined after isokinetic strength assessment. Group A was composed of players who did not show any imbalance in the isokinetic assessment, and Group B was composed of players with any kind of imbalance:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eBilateral H asymmetry was defined as a difference in muscle strength\u0026thinsp;\u0026gt;\u0026thinsp;15% between the right and left sides, either on concentric 60 deg/s or eccentric 30 deg/s analysis\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eThe standard ratio between H and Q was considered abnormal if it was less than 0.47 or 0.45 for Cybex or Contrex, respectively, in the concentric or eccentric analysis. Similarly, the mixed ratio was considered abnormal if the H/Q ratio was less than 0.8 or 0.89 for Cybex or Contrex, respectively.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eThe combination of these two imbalances.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eThe sample size was estimated to guarantee satisfactory accuracy of the primary endpoint. With four clubs, approximately 120\u0026ndash;150 professional rugby players could be expected. Therefore, for a H injury rate close to 15%, the 95% CI had an accuracy of 5%.\u003c/p\u003e \u003cp\u003eStatistical analysis was performed via Stata software (version 15; StataCorp, College Station, Texas, USA). All tests were two-sided, with an alpha level set at 5%. Categorical data are expressed as the number of players and percentages, and continuous data are expressed as the mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation or median [25th ; 75th percentiles], according to their statistical distribution. Comparisons between groups A and B were carried out via the following statistical tests: the chi-square test or Fisher\u0026rsquo;s exact test for categorical variables and Student\u0026rsquo;s t test or the Mann‒Whitney test for quantitative variables. The rate of H injuries was presented with a 95% CI estimated by a binomial distribution. The factors associated with H injuries were studied via generalized linear mixed models (with a logit link function) to consider a cluster (club) effect. The results are expressed as odds ratios (ORs) and 95% CIs. Finally, a multivariable analysis was performed with the same statistical model, with covariates determined according to univariate results and clinical relevance (groups A and B, field position and history of H injury)\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eEquity, diversity and inclusion statement\u003c/h2\u003e \u003cp\u003eThe study population is made up entirely of male players, as rugby is not a mixed sport at the professional level. The research team is mixed. Race/ethnicity/culture was not assessed, but French rugby clubs are known to be plural. No discrimination was made during recruitment, as almost all players from the participating clubs were included.\u003c/p\u003e \u003c/div\u003e"},{"header":"RESULTS","content":"\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eParticipants\u003c/h2\u003e \u003cp\u003eA total of 134 professional rugby players from four \u0026ldquo;top 14\u0026rdquo; clubs were included in this study (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eGroup A (no muscle strength imbalance) consisted of 62 players, whereas Group B (the presence of an imbalance) consisted of 72 players. In this sample, 23.9% of the players had a previous history of H injury, 30.6% in Group A versus 18.1% in Group B. There was no significant difference between the two groups in terms of BMI, distribution of field positions, previous injury or extensibility parameters \u003cb\u003e(\u003c/b\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e\u003cb\u003e).\u003c/b\u003e\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCharacteristics of the participants at baseline (n\u0026thinsp;=\u0026thinsp;134).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTotal\u003c/p\u003e \u003cp\u003e(n\u0026thinsp;=\u0026thinsp;134)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eGroup\u0026nbsp;A\u003c/p\u003e \u003cp\u003e(n\u0026thinsp;=\u0026thinsp;62)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eGroup\u0026nbsp;B\u003c/p\u003e \u003cp\u003e(n\u0026thinsp;=\u0026thinsp;72)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003ep\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eBody mass index (kg/m\u003c/b\u003e\u003csup\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sup\u003e\u003cb\u003e)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e29.6\u0026nbsp;\u0026plusmn;\u0026nbsp;3.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e29.6\u0026nbsp;\u0026plusmn;\u0026nbsp;3.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e29.6\u0026nbsp;\u0026plusmn;\u0026nbsp;3.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.95\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eField position (by number)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.69\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u0026ndash;5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e61 (45.5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e30 (48.4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e31 (43.0)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u0026ndash;8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e19 (14.2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e9 (14.5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10 (13.9)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e9\u0026ndash;10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e17 (12.7)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8 (12.9)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e9 (12.5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e11\u0026ndash;12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e20 (14.9)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10 (16.1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10 (13.9)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e13\u0026ndash;15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e17 (12.7)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5 (8.1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e12 (16.7)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eHistory of hamstring injury\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e32 (23.9)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19 (30.6)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13 (18.1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.088\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eExtensibility of thigh muscles\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRight hamstring (degrees)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e82.9\u0026nbsp;\u0026plusmn;\u0026nbsp;10.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e82.3\u0026nbsp;\u0026plusmn;\u0026nbsp;11.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e83.4\u0026nbsp;\u0026plusmn;\u0026nbsp;9.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.52\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLeft hamstring (degrees)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e81.6\u0026nbsp;\u0026plusmn;\u0026nbsp;10.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e81.4\u0026nbsp;\u0026plusmn;\u0026nbsp;11.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e81.7\u0026nbsp;\u0026plusmn;\u0026nbsp;9.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.85\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRight quadriceps (cm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e8 [0; 12]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6 [2; 12]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e9 [0; 13]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.60\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLeft quadriceps (cm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e8 [0; 13]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6 [2; 13]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e9 [0; 13]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.71\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c5\" namest=\"c1\"\u003e \u003cp\u003e\u003cem\u003eData are presented as number of players (percentages in columns), mean\u0026nbsp;\u0026plusmn;\u0026nbsp;standard deviation or median [25th ; 75th percentiles]. Group\u0026nbsp;A: players without muscle strength imbalance; Group\u0026nbsp;B: players with muscle strength imbalance.\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eAnalysis of the primary endpoint\u003c/h2\u003e \u003cp\u003eDuring the season, the rate of H injuries was 29.9% (95% CI: 22.2\u0026ndash;38.4%), with fewer injuries in Group A than in Group B (21.0%, 95% CI: 11.6\u0026ndash;33.2% versus 37.5%, 95% CI: 26.3\u0026ndash;49.7%, respectively).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eAnalysis of secondary endpoints\u003c/h2\u003e \u003cp\u003eFactors associated with H injury during the 12-month follow-up of the players are presented in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Players with a history of H injury had an increased risk of H injury during the season (OR: 2.65, 95% CI: 1.03\u0026ndash;6.81, p\u0026thinsp;=\u0026thinsp;0.043).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eFactors associated with hamstring injury after 12 months of prospective follow-up (univariate analysis).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNo injury\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eInjury\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eOR [95%CI]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003ep\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGroup\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eA (n\u0026thinsp;=\u0026thinsp;62)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e49 (79.0)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e13 (21.0)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRef.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eB (n\u0026thinsp;=\u0026thinsp;72)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e45 (62.5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e27 (37.5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.12 [0.93; 4.83]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.073\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eBody mass index (kg/m\u003c/b\u003e\u003csup\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sup\u003e\u003cb\u003e)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e29.3\u0026nbsp;\u0026plusmn;\u0026nbsp;3.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e30.1\u0026nbsp;\u0026plusmn;\u0026nbsp;4.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.06 [0.94; 1.18]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.33\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eField position (by number)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u0026ndash;5 (n\u0026thinsp;=\u0026thinsp;61)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e43 (70.5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e18 (29.5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRef.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u0026ndash;8 (n\u0026thinsp;=\u0026thinsp;19)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e13 (68.4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6 (31.6)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.27 [0.38; 4.20]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.69\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e9\u0026ndash;10 (n\u0026thinsp;=\u0026thinsp;17)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e14 (82.4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3 (17.6)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.60 [0.14; 2.51]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.48\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e11\u0026ndash;12 (n\u0026thinsp;=\u0026thinsp;20)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e12 (60.0)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8 (40.0)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.85 [0.59; 5.77]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.29\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e13\u0026ndash;15 (n\u0026thinsp;=\u0026thinsp;17)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e12 (70.6)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5 (29.4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.17 [0.11; 0.83]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.81\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eHamstring injury history\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNo (n\u0026thinsp;=\u0026thinsp;102)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e75 (73.5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e27 (26.5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRef.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eYes (n\u0026thinsp;=\u0026thinsp;32)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e19 (59.4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e13 (40.6)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.65 [1.03; 6.81]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.043\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eExtensibility of thigh muscles\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRight hamstring (degrees)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e83.2\u0026nbsp;\u0026plusmn;\u0026nbsp;10.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e82.1\u0026nbsp;\u0026plusmn;\u0026nbsp;10.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.98 [0.94; 1.02]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.36\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLeft hamstring (degrees)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e81.9\u0026nbsp;\u0026plusmn;\u0026nbsp;10.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e80.7\u0026nbsp;\u0026plusmn;\u0026nbsp;10.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.99 [0.95; 1.03]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.54\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRight quadriceps (cm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5 [0; 12]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e11 [7; 15]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.08 [0.98; 1.17]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLeft quadriceps (cm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6 [0; 12]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e11 [6; 15]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.07 [0.98; 1.16]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.092\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c5\" namest=\"c1\"\u003e \u003cp\u003e\u003cem\u003eData are presented as number of players (percentages in rows), mean\u0026nbsp;\u0026plusmn;\u0026nbsp;standard deviation or median [25th ; 75th percentiles]. CI: confidence interval; Group\u0026nbsp;A: players without muscle strength imbalance; Group\u0026nbsp;B: players with muscle strength imbalance; OR: odds ratio; Ref: reference.\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eAccording to the multivariable analysis (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), players in Group B had an increased risk of H injury compared with players in Group A (OR: 2.65, 95% CI: 1.08\u0026ndash;6.44, p\u0026thinsp;=\u0026thinsp;0.032), as did players with H injury history (OR: 2.96, 95% CI: 1.06\u0026ndash;8.28, p\u0026thinsp;=\u0026thinsp;0.039), whereas players\u0026rsquo; field position was not significantly associated with H injury.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eFactors associated with hamstring injury after 12 months of prospective follow-up (multivariable analysis).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOR [95%CI]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ep\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGroup\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eA (n\u0026thinsp;=\u0026thinsp;62)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRef.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eB (n\u0026thinsp;=\u0026thinsp;72)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.65 [1.08; 6.44]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.032\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eHamstring injury history\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNo (n\u0026thinsp;=\u0026thinsp;102)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRef.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eYes (n\u0026thinsp;=\u0026thinsp;32)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.96 [1.06; 8.28]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.039\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eField position (by number)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u0026ndash;5 (n\u0026thinsp;=\u0026thinsp;61)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRef.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u0026ndash;8 (n\u0026thinsp;=\u0026thinsp;19)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.17 [0.34; 3.97]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.80\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e9\u0026ndash;10 (n\u0026thinsp;=\u0026thinsp;17)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.61 [0.13; 2.65]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.51\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e11\u0026ndash;12 (n\u0026thinsp;=\u0026thinsp;20)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.42 [0.42; 4.77]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.57\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e13\u0026ndash;15 (n\u0026thinsp;=\u0026thinsp;17)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.81 [0.20; 3.19]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.76\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c3\" namest=\"c1\"\u003e \u003cp\u003e\u003cem\u003eCI: confidence interval; Group\u0026nbsp;A: players without muscle strength imbalance; Group\u0026nbsp;B: players with muscle strength imbalance; OR: odds ratio; Ref: reference.\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe rate of H injury during the season increased significantly according to the group and history of H injury: 20.9% (9/43) in Group A players without a history of H injury, 21.1% (4/19) in Group A players with a history of H injury, 30.5% (18/59) in Group B players without a history of H injury, and 69.2% (9/13) in Group B players with a history of H injury (p\u0026thinsp;=\u0026thinsp;0.014).\u003c/p\u003e \u003c/div\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eIn recent years, there has been a particular interest in the prevention of muscle injuries in sports, especially in H, which explains the abundance of scientific work on this subject in the literature\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e,\u003cspan additionalcitationids=\"CR32 CR33 CR34\" citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e. Although this risk of injury is multifactorial in origin, the presence of a lower limb muscle strength imbalance nevertheless plays a fundamental role.\u003c/p\u003e \u003cp\u003eThe main objective of this study was to assess the rate of H injuries in a sample of \u0026ldquo;Top 14\u0026rdquo; professional rugby players over the course of a sporting season. The rate of H injuries was 29.9% (95% CI: 22.2\u0026ndash;38.4%), which is higher than the expected results (13\u0026ndash;23%) and the data in the literature\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eAs the power developed during repeated thrusting efforts or during tackling in rugby is greater than that developed in football, it may seem legitimate to observe a greater rate of injury in this sport. In parallel, the higher the training load is, the greater the risk of injury. Other studies on the occurrence of injury in this sport have widely recognized that as the intensity, duration and load of a training session or match increases, so does the incidence of injury\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e,\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e. Furthermore, many studies on the incidence of injuries have been carried out on relatively heterogeneous samples, including professionals, semiprofessionals and even amateurs, which is not the case in our study, where all the players belong to a \u0026ldquo;Top 14\u0026rdquo; club.\u003c/p\u003e \u003cp\u003ePlayers with a muscular imbalance (either a bilateral asymmetry of the H or an anterior‒posterior imbalance in the H/Q pair) at the start of the season had an increased risk of H injury compared with players without an imbalance (OR: 2.65, 95% CI: 1.08\u0026ndash;6.44, p\u0026thinsp;=\u0026thinsp;0.032), regardless of injury history and field position.\u003c/p\u003e \u003cp\u003eThe rate of H injuries remains higher than expected. This variability could be explained by the greater or lesser proportion of players with a muscular imbalance at the start of the season, who are at risk of injury that is twice as high during the season. Particular attention should therefore be paid to this category of players during the season.\u003c/p\u003e \u003cp\u003eFurthermore, players with a history of H injury had a high risk of injury (OR: 2.96, 95% CI: 1.06\u0026ndash;8.28, p\u0026thinsp;=\u0026thinsp;0.039), which is consistent with the literature\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. We have also shown that, in this sample of professional rugby players, this excess risk is independent of preseason isokinetic assessment and field position.\u003c/p\u003e \u003cp\u003eConcerning the lack of extensibility of thigh muscles, the presence of H or Q retraction was not associated with an increased risk of injury in our study. Witvrouw et al. reported that H and Q tightness was a risk factor for injury to these muscle groups\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. To our knowledge, no other study has examined this association under similar conditions, i.e., with a prospective study over 12 months, thus limiting the comparison of our results with the literature.\u003c/p\u003e \u003cp\u003eAnalysis according to the players\u0026rsquo; field position reveals that there is no position more at risk of muscle injuries. Nevertheless, the question of which field position is most exposed remains open.\u003c/p\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eLimitations\u003c/h2\u003e \u003cp\u003eWe can mention some incomplete collection of data by the clubs, which can be explained, on the one hand, by the difficulties encountered in collecting the data (regular reminders to the club physicians) and, on the other hand, by the permanent flow of arrivals and departures of players at this time of the sports season.\u003c/p\u003e \u003cp\u003eIn addition, there is a potential measurement bias because not all clubs had the same isokinetic dynamometer for measuring muscle strength and because the measurement was carried out by different physicians. Of the four clubs that met the requirements, two had a Cybex dynamometer, and two had a Contrex dynamometer. To limit this bias, we used thresholds specific to each dynamometer to establish the normality of the muscle strength ratios on the basis of the work of Croisier et al.\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eH muscle injury was defined by clinical examination and by being unfit for competition for more than two weeks. However, the stage of the injury and the exact duration of unavailability were not reported for each injury, which would have allowed for a more refined interpretation of these results. Furthermore, it would have been relevant to collect the training and match time of the players to relate our results to a physical load (risk of injury per minute of training/match).\u003c/p\u003e \u003cp\u003eThe type of pitch on which the injury occurred was not taken into account. We know that the risk of injury also varies according to the type of pitch. Among synthetic turf, this risk also varies because the new materials used in the latest generation of synthetic turf allow for greater shock absorption. These are characterized by longer fibers and synthetic rubber elements, which reduce the frictional forces and the stiffness of the ground.\u003c/p\u003e \u003cp\u003eFinally, it would have been interesting to integrate additional epidemiological data (e.g., the ethnic origin of players) as well as the distribution of these injuries throughout the season, which would allow a more precise analysis of the circumstances of the occurrence of these injuries. The impact of a busy schedule is still being debated. The idea is to implement preventive measures at the right moment in the season. We know that this incidence usually tends to increase progressively during the season, especially for clubs taking part in numerous competitions, as was the case for this sample of players (championship, cups, etc.)\u003csup\u003e\u003cspan additionalcitationids=\"CR37\" citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e"},{"header":"CONCLUSION","content":"\u003cp\u003eThese results show that the rate of H injuries in professional rugby is high. An imbalance in the isokinetic balance in the preseason is a risk factor for the occurrence of an injury during the season. This knowledge can be used to implement prevention strategies in professional sports.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eBMI: body mass index\u003c/p\u003e\n\u003cp\u003eCI: confidence interval\u003c/p\u003e\n\u003cp\u003eH: hamstring\u003c/p\u003e\n\u003cp\u003eOR: odds ratio\u003c/p\u003e\n\u003cp\u003eQ: quadriceps\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthical approval information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was conducted at the Clermont-Ferrand University Hospital. All procedures concerning the participants were carried out in accordance with the ethical standards of the Interregional Ethics Committee. A favorable ethical opinion was delivered by the inter-regional ethics committee \u0026ldquo;\u003cem\u003eComit\u0026eacute; d\u0026rsquo;Ethique des Centres d\u0026rsquo;Investigation Clinique de l\u0026rsquo;inter-r\u0026eacute;gion Rh\u0026ocirc;ne-Alpes \u0026ndash;Auvergne\u003c/em\u003e\u0026rdquo; whose file number is: CE-CIC-GREN-11/23 obtained in January 2012.\u0026nbsp;In accordance with current regulations and the principles outlined in the Declaration of Helsinki, all participants were informed in a clear, comprehensible, and appropriate manner about the objectives, procedures, potential benefits, and possible risks associated with their participation in the study. Participation was voluntary, and a \u003cstrong\u003enon-objection form\u003c/strong\u003e was completed in cases where individuals declined to take part. No identifying patient data are included in this manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003ch3\u003eCompeting interests:\u003c/h3\u003e\n\u003cp\u003eNo potential conflicts of interest declared.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNone\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026rsquo; contributions\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe guarantor is the name of the corresponding author; whose initials are MG. The conception and design of the study was made by EC, MJ and DM. The drafting of the original protocol by EC, MJ, DM and CL. The coordination of the study by EC. The acquisition of data by MG. The design of the statistical analysis plan by BP and CL. The drafting of the present manuscript by MG, MPV and EC. The final approval by all authors. \u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eEkstrand J, Hagglund M, Walden M. Injury incidence and injury patterns in professional football: the UEFA injury study. \u003cem\u003eBr J Sports Med\u003c/em\u003e. 2011;45(7):553-558. doi:10.1136/bjsm.2009.060582\u003c/li\u003e\n\u003cli\u003eHawkins R, Hulse M, Wilkinson C, Hodson A, Gibson M. The association football medical research programme: an audit of injuries in professional football. \u003cem\u003eBr J Sports Med\u003c/em\u003e. 2001;35(1):43-47. doi:10.1136/bjsm.35.1.43\u003c/li\u003e\n\u003cli\u003eHenderson G, Barnes CA, Portas MD. 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Inter-machine reliability of the Biodex and Cybex isokinetic dynamometers for knee flexor/extensor isometric, concentric and eccentric tests. \u003cem\u003ePhys Ther Sport Off J Assoc Chart Physiother Sports Med\u003c/em\u003e. 2015;16(1):59-65. doi:10.1016/j.ptsp.2014.04.004\u003c/li\u003e\n\u003cli\u003eMaffiuletti NA, Bizzini M, Desbrosses K, Babault N, Munzinger U. Reliability of knee extension and flexion measurements using the Con-Trex isokinetic dynamometer. \u003cem\u003eClin Physiol Funct Imaging\u003c/em\u003e. 2007;27(6):346-353. doi:10.1111/j.1475-097X.2007.00758.x\u003c/li\u003e\n\u003cli\u003eCroisier JL, Ganteaume S, Binet J, Genty M, Ferret JM. 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Incidence, site, and nature of injuries in amateur rugby league over three consecutive seasons. \u003cem\u003eBr J Sports Med\u003c/em\u003e. 2000;34(2):98-103. doi:10.1136/bjsm.34.2.98\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"bmc-sports-science-medicine-and-rehabilitation","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ssmr","sideBox":"Learn more about [BMC Sports Science, Medicine and Rehabilitation](http://bmcsportsscimedrehabil.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/ssmr/default.aspx","title":"BMC Sports Science, Medicine and Rehabilitation","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Epidemiology, injury prevention, isokinetic, muscle injury, rugby","lastPublishedDoi":"10.21203/rs.3.rs-6445849/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6445849/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground:\u003c/strong\u003eHamstring injuries (HI) are among the most common muscle injuries in team ball sports. Hamstring strenght deficit is an intrinsic risk factor for HI.\u003c/p\u003e\n\u003cp\u003eTo evaluate the rate of occurrence of HI in male professional rugby “Top 14” players during one season and to study the possible relationships among hamstring strength deficit (evaluated by isokinetic dynamometry), muscle extensibility defects, field position and the risk of HI.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eStudy Design: \u003c/strong\u003eDescriptive epidemiology study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods:\u003c/strong\u003eThe rate of HI was prospectively studied in 134 professional rugby players from four French professional teams over one competitive season. Preseason isokinetic and muscle extensibility tests were performed. The recorded information included the field position and history of injuries. The analysis was performed by comparing two groups: without (Group A) and with (Group B) preseason isokinetic imbalance.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults:\u003c/strong\u003e During the season, the rate of HI was 29.9% (95% CI: 22.2-38.4%), with fewer injuries in Group A than in Group B (21.0%, 95% CI: 11.6-33.2% versus 37.5%, 95% CI: 26.3-49.7%, respectively). According to the multivariable analysis, Group B had an increased risk of HI compared with Group A (OR: 2.65, 95% CI: 1.08-6.44, \u003cstrong\u003ep=0.032\u003c/strong\u003e), as did the players with a history of HI (OR: 2.96, 95% CI: 1.06-8.28, \u003cstrong\u003ep=0.039\u003c/strong\u003e), whereas the players’ field position was not significantly associated with HI.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusion:\u003c/strong\u003e The rate of HI among professional rugby players is high. An isokinetic imbalance in the preseason is a risk factor for injury during the season. This knowledge can be used to implement prevention strategies in professional sports.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClinical trial number\u003c/strong\u003e : Not applicable\u003c/p\u003e","manuscriptTitle":"Male professional rugby players with hamstring/quadriceps muscle imbalance have an increased risk of hamstring injuries during the season","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-20 12:16:39","doi":"10.21203/rs.3.rs-6445849/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"259389941602207553514235556349197557644","date":"2025-05-23T20:25:38+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-05-16T09:44:17+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-05-13T06:07:13+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-04-24T06:22:27+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-04-23T13:50:52+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Sports Science, Medicine and Rehabilitation","date":"2025-04-23T13:49:43+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-sports-science-medicine-and-rehabilitation","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ssmr","sideBox":"Learn more about [BMC Sports Science, Medicine and Rehabilitation](http://bmcsportsscimedrehabil.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/ssmr/default.aspx","title":"BMC Sports Science, Medicine and Rehabilitation","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"e43b1360-771f-4c4b-808b-1a2a16aa2a95","owner":[],"postedDate":"May 20th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-05-20T12:16:39+00:00","versionOfRecord":[],"versionCreatedAt":"2025-05-20 12:16:39","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6445849","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6445849","identity":"rs-6445849","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}