Is estimation of Floquet multipliers of human walking valid?

The Floquet multiplier has been widely used to assess orbital stability of human walking. Floquet introduced it to quantify the stability of periodic motion of deterministic linear systems, but human walking involves highly nonlinear dynamics and inevitable noise. This preliminary study addresses the validity of Floquet multiplier estimation of a nonlinear system with stochastic noise. Noise was added to a simplified but nonlinear model of human walking so that the variability of model walking was comparable to that of human walking. Results show that linear regression yields a biased measure of the Floquet multiplier though its accuracy improves with a sufficient number of strides.