Nonlinear dynamics of running: Speed, stability, symmetry and the effects of leg amputations

TL;DR

This study investigates how leg amputations affect running stability by analyzing Lyapunov exponents, revealing that prosthetic legs are less stable but runners compensate through control of their center-of-mass.

Contribution

It provides novel insights into the stability differences between biological and prosthetic legs during running and how runners adapt to asymmetries.

Findings

Prosthetic legs exhibit less stability than biological legs.

Runners with amputations have slightly more stable center-of-mass dynamics.

Runners compensate for leg asymmetries through control of their center-of-mass.

Abstract

In this paper, we study dynamic stability during running, focusing on the effects of speed and the use of a leg prosthesis. We compute and compare the maximal Lyapunov exponents of kinematic time-series data from subjects with and without unilateral transtibial amputations running at a wide range of speeds. We find that the dynamics of the affected leg with the running-specific prosthesis are less stable than the dynamics of the unaffected leg, and also less stable than the biological legs of the non-amputee runners. Surprisingly, we find that the center-of-mass dynamics of runners with two intact biological legs are slightly less stable than those of runners with amputations. Our results suggest that while leg asymmetries may be associated with instability, runners may compensate for this effect by increased control of their center-of-mass dynamics.