Abstract

Spring-like leg behavior is a general feature of mammalian bouncing gaits, such as running and hopping. Although increases in step frequency at a given running speed are known to increase the stiffness of the leg spring (kleg) in non-amputees, little is known about stiffness regulation in unilateral transfemoral amputees. In this study, we investigated stiffness regulation at different step frequencies at a given running speed in unilateral transfemoral amputees. We recruited nine unilateral transfemoral amputees wearing running-specific prostheses. They were asked to perform the action of running across a range of step frequencies (±20, ±15, ±10, ±5, and 0% of their preferred step frequency) at a given speed on an instrumented treadmill. The kleg values were calculated using ground reaction force data in both the affected and unaffected limbs. It was found that kleg increased with increasing step frequency for the unaffected limb, but not for the affected limb. Consequently, the unilateral transfemoral amputees attained the desired step frequency in the unaffected limb, but were unable to match the three highest step frequencies using their affected limbs. These results suggest that the stiffness regulation strategy during running differs between the affected and unaffected limbs.

Highlights

  • Spring-like leg behavior is a general feature of mammalian bouncing gaits, such as running and hopping

  • Because spring-like leg behavior is a general feature of mammalians bouncing gaits, an improved understanding of the frequency-dependent modulation of leg stiffness regulation will provide insight into the neuromechanical principles of legged locomotion in humans

  • Stiffness regulation during running across a range of fstep has been examined in unilateral transtibial amputees, where kleg was increased in the unaffected limb but was unchanged in the affected limb[7]

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Summary

Introduction

Spring-like leg behavior is a general feature of mammalian bouncing gaits, such as running and hopping. Stiffness regulation during running across a range of fstep has been examined in unilateral transtibial amputees, where kleg was increased in the unaffected limb but was unchanged in the affected limb[7]. Because fstep is associated with running velocity, physiological responses, and potential injury risks[8,9,10], knowledge of how unilateral TFAs adjust stance leg mechanics for increasing fstep at a given running velocity may help in developing effective running-gait rehabilitation and individualized specifications of RSPs. this study investigated stiffness regulation during running at different fstep values at a given running speed in unilateral TFAs wearing RSPs. A recent finding showed that an athlete with unilateral transtibial amputation was unable to match relatively lower and higher hopping frequencies as a consequence of the invariant leg spring stiffness of the affected limb during one-legged hopping[11]. The slopes (dotted lines) of these curves represent the vertical stiffness (kvert). kvert is the slope of the vGRF–COM displacement curve in the leg compression phase

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