Risk Factors for Lower Extremity Muscle Injury in Professional Soccer

BACKGROUND: Muscle injury is the most common injury type in professional soccer players. Despite this, risk factors for common lower extremity injuries remain elusive. PURPOSE: To evaluate the effects of various player- and match-related risk factors on the occurrence of lower extremity muscle injury in male professional soccer. STUDY DESIGN: Cohort study; level of evidence, 2. METHODS: Between 2001 and 2010, 26 soccer clubs (1401 players) from 10 European countries participated in the study. Individual player exposure and time loss muscle injuries in the lower extremity were registered prospectively by the club medical staffs during 9 consecutive seasons. Hazard ratios (HRs) were calculated for player-related factors from simple and multiple Cox regression, and odds ratios (ORs) were calculated for match-related variables from simple and multiple logistic regression, presented with 95% confidence intervals (CIs). RESULTS: There were 2123 muscle injuries documented in the major lower extremity muscle groups: adductors (n = 523), hamstrings (n = 900), quadriceps (n = 394), and calf (n = 306). Injuries to the adductors (56%; P = .015) and quadriceps (63%; P< .001) were more frequent in the kicking leg. Multiple analysis indicated that having a previous identical injury in the preceding season increased injury rates significantly for adductor (HR, 1.40; 95% CI, 1.00-1.96), hamstring (HR, 1.40; 95% CI, 1.12-1.75), quadriceps (HR, 3.10; 95% CI, 2.21-4.36), and calf injuries (HR, 2.33; 95% CI, 1.52-3.57). Older players (above mean age) had an almost 2-fold increased rate of calf injury (HR, 1.93; 95% CI, 1.38-2.71), but no association was found in other muscle groups. Goalkeepers had reduced injury rates in all 4 muscle groups. Match play on away ground was associated with reduced rates of adductor (OR, 0.56; 95% CI, 0.43-0.73) and hamstring injuries (OR, 0.76; 95% CI, 0.63-0.92). Quadriceps injuries were more frequent during preseason, whereas adductor, hamstring, and calf injury rates increased during the competitive season. CONCLUSION: Intrinsic factors found to increase muscle injury rates in professional soccer were previous injury, older age, and kicking leg. Injury rates varied during different parts of the season and also depending on match location.