(a) Example of time series of stride time during 1 h of walking in a healthy young adult at slow, normal, and fast walking rates, and below, after the fast data set is randomly shuffled. (b) While there are subtle effects of gait speed, DFA shows that there is fractal scaling at all three gait speeds. When the data are randomly reordered (shuffled), the slope becomes 0.5, reflecting white noise and an absence of fractal scaling [From J. M. Hausdorff, P. L. Purdon, C. K. Peng, Z. Ladin, J. Y. Wei, and A. L. Goldberger, “Fractal dynamics of human gait: stability of long-range correlations in stride interval fluctuations,” J. Appl. Physiol. 80, 1448 (1996). Copyright ©1996 by American Physiological Society. Reprinted by permission of American Physiological Society]. Data can be downloaded from www.physionet.org. Strictly speaking, Figs. 345 should be plotted as discrete points rather than points joined with lines. The points are joined together as a continuous line, however, since this makes it somewhat easier to visualize the dynamics.