Between-limb asymmetries during running are often evaluated to assess injury risk or recovery. Asymmetries less than 10% are generally considered normal, but it is unknown if asymmetries vary depending on the metric of interest, the athlete`s sex, or running speed. Purpose The primary aims of this investigation were to describe the magnitude of asymmetries of common variables during running among healthy athletes and to determine if sex and speed influence magnitudes of asymmetry. Methods This study analyzed routinely collected running gait data on healthy Division I collegiate athletes. All athletes had no history of lower extremity surgery, no lower extremity injuries for 3 months before testing, and running data available at 2.68, 2.95, 3.35, 3.80, and 4.47 m·s-1. Asymmetries were calculated for ground reaction forces, spatiotemporal metrics, joint kinematics, and joint kinetics. Separate linear mixed-effects models assessed the influence of sex, speed, and the interaction on asymmetries of interest. z Scores were calculated for significant effects to further assess the magnitude of differences. Results Results from 204 athletes were included. The magnitude of asymmetry varied depending on the variable of interest, with asymmetries =3° observed for joint kinematics and greater asymmetries observed among joint work asymmetries ranging from 10% to 40%. No significant interactions between sex and speed were observed. Differences in sex and speed were noted; however, the effect sizes were very small based on z score comparison (-0.17 = z = 0.36) and were unlikely to be meaningful. Conclusions The magnitude of asymmetry varies considerably depending on the running gait variable. Interpretation of between-limb asymmetry in running mechanics needs to be specific to the variable of interest, whereas sex or running speed seem to be minor factors.
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