PURPOSE: The aim of this study was to investigate the effect of altering preferred running speed by ±20% on kinetic asymmetry. METHODS: Three-dimensional motion analysis and force data were acquired from 15 healthy males (age, 27 ± 4.6 yr; height, 1.81 ± 0.09 m; mass, 80.4 ± 12.4 kg) during their preferred running speed and at ±20% of this speed. Three-tesla magnetic resonance images were used to measure Achilles tendon cross-sectional area and moment arm, for use in calculation of tendon stress. Kinetic and tendon stress asymmetry were subsequently calculated in each condition using the symmetry index. RESULTS: Across all joints and conditions, the average asymmetry of peak moments was between ±6%, but higher individual values were observed. There was no effect of speed on the magnitude of asymmetry. Ground contact times, vertical ground reaction forces, and support and ankle moments (maximum absolute asymmetry, 9%) were more symmetrical than hip and knee moments (up to 18%). Individual joint contribution to support moment and positive work were similar in both limbs, and ankle and hip compensatory interactions were observed with alterations in running speed. Achilles tendon stress increased with increased running speed, with higher stress in the preferred limb; asymmetry in tendon stress was not related to asymmetry in vertical ground reaction forces. CONCLUSION: Results show small effects of altering running speed on kinetic asymmetry, but responses are individual specific with interactions occurring between joints to maintain overall movement symmetry. Further research is needed to understand the mechanical and neuromuscular mechanisms underpinning these compensations.
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