Short-term step-to-step correlation in plantar pressure distributions during treadmill walking, and implications for footprint trail analysis

- This is the first study to explicitly examine short-term gait-cycle correlations.
- Step-to-step autocorrelations in plantar pressure distributions were calculated.
- Step-to-step correlations were weak across the whole plantar surface.
- Support is provided for regarding neighboring footsteps as independent samples.

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 1.1 m/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.