Inter-limb differences in in-vivo tendon behavior, kinematics, kinetics and muscle activation during running.

Overloading of tendon tissue may result in overuse tendon injuries in runners. One possible cause of overloading could be the occurrence of biomechanical inter-limb differences during running. However, scarce information exists concerning the simultaneous analysis of inter-limb differences in external and internal loading-related variables in habitual runners. In this study ground reaction force, joint kinematics, triceps surae and tibialis anterior activations, and medial gastrocnemius muscle-tendon junction displacement were assessed bilaterally during treadmill running at 2.7 m.s-1 and 4.2 m.s-1. Statistical parametric t-tests and effect sizes were calculated to identify eventual inter-limb differences across the stance phase and stride cycle. Hip flexion angle was 9° greater (p = 0.03, ES = 0.30) in the non-preferred limb during the flight phase at 4.2 m.s-1. Hip extension velocity was 45 deg.s-1 greater (p = 0.04, ES = 0.41) during ground contact and 25 deg.s-1 greater (p = 0.02, ES = 0.41) immediately after toe-off in the non-preferred limb at 4.2 m.s-1. Hip extension velocity was also 40 deg.s-1 greater (p = 0.01, ES = 0.46) in the non-preferred limb prior to touch-down at 4.2 m.s-1. Brief inter-limb differences in joint kinematics were not accompanied by inter-limb differences in variables associated to internal loading, suggesting they are unlikely to be underlying factors leading to tendon overloading in healthy non-injured runners.