Neuromechanical contributions to lower extremity stiffness differ between single leg hopping and running

In human locomotion, lower extremity stiffness (KLeg) describes how subjects attenuate load during ground contact. Greater KLeg is associated with increased risk for lower extremity injury. We analysed the neuromechanical contributions to KLeg during running and single leg hopping in healthy runners. We found that greater KLeg during single leg hopping was significantly associated with greater ankle plantarflexor musculotendinous stiffness (MTS), greater ankle plantarflexor muscle activation (EMG) and greater hopping frequency. Greater KLeg during running was significantly associated with greater knee extensor MTS, lesser hip internal range of motion (ROM) and greater running velocity. Our findings suggest that KLeg during hopping was predominantly modulated by ankle musculature whereas KLeg during running was predominantly modulated by knee musculature.