An entropy approach for evaluating adaptive motor learning processes while walking with unstable footwear

This study evaluated the short- and long-term effects of unstable shoes (US) on the structure/shape of variability in gait. Therefore, sample entropy (SEn) values of centre of mass velocity (vCOM) signals in medio-lateral (ML), anterior-posterior (AP) and vertical (VT) direction were computed for 12 sport students during walking with US and flat shoes (FS) before and after a 10-week accommodation period. Statistical analysis included two-way repeated-measures ANOVA followed by post hoc tests where appropriate (α = 0.05). Most noteworthy, it was found that (1) when compared to FS, using US increased the predictability of vCOM time series, not necessarily always at pre-test, but especially at post-test since (2) the corresponding SEn values decreased for the US condition while remaining stable for the FS condition during the interval between laboratory visits, although (3) the related shoe-by-visit interaction effects were only significant for vCOMML data and not for vCOMAP nor for vCOMVT data. Accordingly, the path of adapting to US was characterised by a “decomplexification” of the motor system; however, the variable practice (i.e., training) loads accompanying such a footwear intervention were probably too small to further expand the overall flexibility capabilities of athletically active persons (in more real-life settings).