Figure 6

Detrended Fluctuation Analysis: surrogate data tests. The time series of stride intervals (Figure 1B) of each subject (#1 to #20) were analyzed by DFA (figure 1C) to determine the scaling exponent α indicating the presence of a long range correlation pattern in stride intervals. Black and white circles are respectively the scaling exponent for Overground Walking (OW) and Treadmill Walking (TW). Each time series was randomly shuffled twenty times to produce 20 surrogate time series. The average of these series is near 0.5 (random process with no correlation). The vertical bars show the extent of 2 times the SD of the 20 surrogate time series. Scaling exponent larger than this value can be considered significantly different from a random uncorrelated series.