Effect of Sex and Level of Activity on Lower Extremity Strength, Functional Performance and Limb Symmetry.

CONTEXT: Strength, functional performance and limb symmetry are common objective clinical assessments used by clinicians to guide safe return to physical activity following injury. Population-specific unilateral limb outcomes or estimates of limb symmetry of these assessments should be established.

OBJECTIVE: To compare lower extremity strength, functional performance and limb symmetry in healthy participants based on sex and level of activity.

DESIGN: Descriptive laboratory study Setting: Laboratory Participants: 117 healthy participants (72 males/45 females, mass=73.67±13.60kg, height=1.76±0.12m, age=21.44±2.92 years) without history of injury within 6 months were included.

INTERVENTIONS: Participants completed isokinetic concentric and isometric knee extension and flexion strength tasks at 90°/s, 180°/s and 90° respectively and four hop tasks(single, crossover, triple, 6m timed) during one session. Groups were separated by sex(male, female) and activity level(athlete, non-athlete). Participants rostered on National Collegiate Athletic Association(NCAA) Division I(DI) teams were considered athletes and non-NCAA DI healthy, uninjured participants were considered non-athletes.

MAIN OUTCOME MEASURES: Limb Symmetry Index(LSI), maximal voluntary isometric contraction(MVIC, Nm/kg), peak torque(Nm/kg), average power(Nm/s), distance(m) and time hopped(s) were assessed. LSI was calculated by dividing the lower limb outcome by the higher limb outcome of the non-dominant or dominant limb. Group differences were assessed through Mann Whitney U tests and Cohen's d effect sizes for all comparisons.

RESULTS: LSI differences did not exist between groups. Mean LSIs for all participants ranged between 83.52±12.54% and 96.16±3.82%. On average, males were stronger (Range d=0.63-1.54), hopped farther (Range d=1.52-1.63) and faster (Range d=1.67-1.68) than females. On average, some strength differences existed between athletes and non-athletes but athletes hopped farther (Range d=0.71-0.82) and faster (Range d=(0.87-0.88) than non-athletes.

CONCLUSIONS: Unilateral limb strength and functional performance outcomes differ between sex and activity level, but not limb symmetry. These differences may be important for a clinician's understanding of normative values of common return to play assessment tasks.