Fractional Langevin model of gait variability.

"AcknowledgementsThe authors thank the U.S. Army Research Office for partial support of this research and Dr. L. Griffin for providing the data used in this analysis and for useful discussions. The nonlinear form of the mass exponent τ(q) in Figure , the convex form of the singularity spectrum f(h) in Figure and the fit to f(q) in Figure , are all indications that interstride interval time series are multifractal. This analysis is further supported by the fact that the maxima of the singularity spectra coincide with the fractal dimensions determined previously using the scaling properties of the time series without the construction of a random walk trajectory []. A complete discussion of the limitations associated with determining the multifractal nature of interstride intervals using the singularity spectrum with limited data is given by Scafetta et al []. Furthermore, the empirical values of the Lévy index in Table are consistent with those predicted using Lévy-walk diffusion relation [] at the 0.01 level of significance."