  In this paper, the diffusion entropy technique is applied to investigate the
scaling behavior of stride interval fluctuations of human gait. The scaling
behavior of the stride interval of human walking at normal, slow and fast rate
are similar; with the scale-invariance exponents in the interval
$[0.663,0.955]$, of which the mean value is $0.821\pm0.011$. Dynamical analysis
of these stride interval fluctuations reveals a self-similar pattern:
Fluctuation at one time scale are statistically similar to those at multiple
other time scales, at least over hundreds of steps, while the healthy subjects
walk at their normal rate. The long-range correlations are observed during the
spontaneous walking after the removal of the trend in the time series with
Fourier filter. These findings uncover that the fractal dynamics of stride
interval of human gait are normally intrinsic to the locomotor systems.
