Mild Quadriceps and Hamstring Strength Deficits do not Persist After Sport-Related Concussion

Risk for lower extremity musculoskeletal injury increases after sport-related concussion (SRC) and may result from unresolved motor control deficits. Muscle weakness is a deficit that could contribute to musculoskeletal injury risk. Athletes with SRC will demonstrate quadriceps and hamstring muscle weakness at the time of return to sport and 30 days later compared with controls. Prospective matched cohort. Level 3. A total of 31 athletes with SRC (CONCUSSION) were matched by sex, age, and activity level to controls (CONTROL). Testing was conducted at initial assessment and 30 days later; initial assessment in CONCUSSION occurred when cleared for return to play. Isokinetic testing assessed quadriceps and hamstring strength of the dominant and nondominant legs at 60 and 180 deg/s. Peak torque values were normalized to body mass (N-m/kg). Data were analyzed with repeated measures general linear models (group × time), and effect sizes were calculated. Analysis at 60 deg/s included 26 matched pairs (15 male per group) and at 180 deg/s included 30 matched pairs (17 males per group). Time from concussion to initial assessment was 21.3 (7.8) mean (standard deviation) days. No significant interactions or main effects were detected ( P > 0.05). Across muscle groups, legs, and testing speeds, effect sizes at initial assessment were small ( d = 0.117 to 0.353), equating to a strength deficit in CONCUSSION of 0.04 to 0.18 N-m/kg, and effect sizes were further reduced at 30-day follow-up (d = −0.191 to 0.252). In athletes with SRC, quadriceps and hamstring strength were decreased only minimally at return to play compared with controls and the difference lessened over 30 days. Strength deficits may not be a major contributor to increased lower extremity musculoskeletal injury risk after SRC. Strength training could be implemented before return to play after SRC to mitigate any strength deficits.