Muscle Strength Is a Poor Screening Test for Predicting Lower Extremity Injuries in Professional Male Soccer Players: A 2-Year Prospective Cohort Study

Background: Lower extremity muscle strength tests are commonly used to screen for injury risk in professional soccer. However, there is limited evidence on the ability of such tests in predicting future injuries. Purpose: To examine the association between hip and thigh muscle strength and the risk of lower extremity injuries in professional male soccer players. Study Design: Case-control study; Level of evidence, 3. Methods: Professional male soccer players from 14 teams in Qatar underwent a comprehensive strength assessment at the beginning of the 2013/2014 and 2014/2015 seasons. Testing consisted of concentric and eccentric quadriceps and hamstring isokinetic peak torques, eccentric hip adduction and abduction forces, and bilateral isometric adductor force (squeeze test at 45°). Time-loss injuries and exposure in training and matches were registered prospectively by club medical staff throughout each season. Univariate and multivariate Cox regression analyses were used to calculate hazard ratios (HRs) with 95% CIs. Results: In total, 369 players completed all strength tests and had registered injury and exposure data. Of these, 206 players (55.8%) suffered 538 lower extremity injuries during the 2 seasons; acute muscle injuries were the most frequent. Of the 20 strength measures examined, greater quadriceps concentric peak torque at 300 deg/s (HR, 1.005 [95% CI, 1.00-1.01]; P =.037) was the only strength measure identified as significantly associated with a risk of lower extremity injuries in multivariate analysis. Greater quadriceps concentric peak torque at 60 deg/s (HR, 1.004 [95% CI, 1.00-1.01]; P =.026) was associated with the risk of overuse injuries, and greater bilateral adductor strength adjusted for body weight (HR, 0.75 [95% CI, 0.57-0.97; P =.032) was associated with a lower risk for any knee injury. Receiver operating characteristic curve analyses indicated poor predictive ability of the significant strength variables (area under the curve, 0.45-0.56). Conclusion: There was a weak association with the risk of lower extremity injuries for 2 strength variables: greater quadriceps concentric muscle strength at (1) high and (2) low speeds. These associations were too small to identify an “at-risk” player. Therefore, strength testing, as performed in the present study, cannot be recommended as a screening test to predict injuries in professional male soccer.