  It has been observed that long time series of Stride Time (ST), Stride Length
(SL) and Stride Speed (SS=SL/ST) exhibited statistical persistence (long-range
auto-correlation) in overground walking. Rhythmic auditory cueing induced
anti-persistent (or anti-correlated) pattern in ST series, while SL and SS
remained persistent. On the other hand, it has been shown that SS became
anti-persistent in treadmill walking, while ST and SL remained persistent. The
aim of this study was to analyze the effect of the combination of treadmill
walking (imposed speed) and auditory cueing (imposed cadence) on gait dynamics.
Twenty middle-aged subjects performed 6 x 5min walking trials at various
imposed speeds on an instrumented treadmill. Freely-chosen walking cadences
were measured during the first three trials, and then imposed accordingly in
the last three trials by using a metronome. Detrended fluctuation analysis
(DFA) was performed on the times series of ST, SL, and SS. Treadmill induced
anti-persistent dynamics in the time series of SS, but preserved the
persistence of ST and SL. On the contrary, all the three parameters were
anti-persistent under dual-constraints condition. Anti-persistent dynamics may
be related to a tighter control: deviations are followed by a rapid
over-correction, what produces oscillations around target values. Under single
constraint condition, while SS is tightly regulated in order to follow the
treadmill speed, redundancy between ST and SL would likely allow persistent
pattern to occur. Conversely, under dual constraint conditions, the absence of
redundancy among SL, ST and SS would explain the generalized anti-persistent
pattern.
