Optimal walking in terms of variability in step length.

The optimal condition in speed, step rate, and step length of human walking has been reported in terms of temporal consistency, energy cost, and attentional demand. No study, however, has been conducted on the optimal condition in terms of spatial variability of walking. This study examined whether there is an optimal walking speed with minimum intrasubject variability in step length and step width during free walk (experiment 1) and whether there is an optimal step rate with minimum step length variability during walking with imposed step rates (experiment 2). Wearing shoes with ink-applied felt squares attached to the heels, healthy students walked on a flat walkway (0.6 x 16 m) at five different speeds with a freely chosen step rate in experiment 1 and walked at three different speeds with five different step rates in experiment 2. Free walk was found to have the fewest variable errors (VEs) in step length approximately at preferred walking speed. Variable error in step width increased linearly with an increase in walking speed. Under imposed step rates, VEs in step length were the fewest when walking with step rates close to those in free walk. Our everyday walking is performed most frequently at preferred speed and/or with freely chosen step rate, thereby optimizing the consistency of gait performance. Intrasubject variability in step length may be a useful measure for evaluation of walking.