Bilateral performance symmetry during drop landing

The assumption that lower extremity function is bilaterally symmetrical is prevalent throughout the biomechanics literature. The unilateral development of many overuse and acute injuries may suggest that this assumption is inaccurate. Analyses of bilateral function report conflicting results and may be partially attributable to the types of movement activities utilized and to research methodology. The purpose of this study was to evaluate the concurrent bilateral performance of the lower extremities during an apparently symmetrical movement task. Concurrent left/right side vertical ground reaction forces (VGRF) and lower extremity joint moments (JM) were obtained for 10 subjects performing 25 voluntary hanging drop landings (60 cm) on each of 3 consecutive days. Bilateral variability (BV) and systematic bilateral asymmetry (BA) were calculated for each trial. Bilateral variability was less for VGRF variables (12.8%) than JM variables (25.3%). Bilateral asymmetry was identified more often among VGRF variables (52.5%) than JM variables (16.7%). The magnitude of identified BA was greater than either the group BV (25%) or BA (110%) and indicates that bilateral differences are biomechanically meaningful.