Article

The gait cycle is continuous, but for practical reasons one is often forced to
analyze one or only a few adjacent cycles, for example in non-treadmill
laboratory investigations and in fossilized footprint analysis. The nature of
variability in long-term gait cycle dynamics has been well-investigated, but
short-term variability, and specifically correlation, which are highly relevant
to short gait bouts, have not. We presently tested for step-to-step
autocorrelation in a total of 5243 plantar pressure (PP) distributions from ten
subjects who walked at 1.1m/s on an instrumented treadmill. Following spatial
foot alignment, data were analyzed both from three points of interest (POI):
heel, central metatarsals, and hallux, and for the foot surface as a whole, in a
mass-univariate manner. POI results revealed low average step-to-step
autocorrelation coefficients (r=0.327+/-0.094; mean+/-st. dev.). Formal
statistical testing of the whole-foot r distributions reached significance over
an average of only 0.42+/-0.52% of the foot's surface, even for a highly
conservative uncorrected threshold of p<0.05. The common assumption, that short
gait bouts consist of independent cycles, is therefore not refuted by the present
PP results.
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