Mechanical and metabolic determinants of the preferred step width in human walking

TLDR

A three‑dimensional model predicts that increases in mechanical and metabolic costs during walking arise from the work needed to redirect the centre‑of‑mass velocity during step‑to‑step transitions. The study measured mechanical work from limb external work and metabolic cost via open‑circuit respirometry across step widths ranging from 0.00 to 0.45 of leg length. Both mechanical and metabolic costs rose sharply (≈54 % and 45 %) for widths wider than the preferred 0.15–0.45 L, while narrower widths increased metabolic cost by 8 %; the resulting trade‑off yields a minimum metabolic cost near 0.12 L, close to foot width, explaining why humans prefer a step width that minimizes metabolic cost.

Abstract

We studied the selection of preferred step width in human walking by measuring mechanical and metabolic costs as a function of experimentally manipulated step width (0.00-0.45L, as a fraction of leg length L). We estimated mechanical costs from individual limb external mechanical work and metabolic costs using open circuit respirometry. The mechanical and metabolic costs both increased substantially (54 and 45%, respectively) for widths greater than the preferred value (0.15-0.45L) and with step width squared (R(2) = 0.91 and 0.83, respectively). As predicted by a three-dimensional model of walking mechanics, the increases in these costs appear to be a result of the mechanical work required for redirecting the centre of mass velocity during the transition between single stance phases (step-to-step transition costs). The metabolic cost for steps narrower than preferred (0.10-0.00L) increased by 8%, which was probably as a result of the added cost of moving the swing leg laterally in order to avoid the stance leg (lateral limb swing cost). Trade-offs between the step-to-step transition and lateral limb swing costs resulted in a minimum metabolic cost at a step width of 0.12L, which is not significantly different from foot width (0.11L) or the preferred step width (0.13L). Humans appear to prefer a step width that minimizes metabolic cost.