  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.
