Voluntary changes in step width and step length during human walking affect dynamic margins of stability.

"Cautious" gait is generally characterized by wider and shorter steps. However, we do not clearly understand the relationship between step characteristics and individuals' stability. Here, we examined the effects of voluntarily altering step width (SW) and step length (SL) on individuals' margins of stability. Fourteen participants completed three 3-min treadmill walking trials during three SL (short, normal with metronome, and long) and three SW (narrow, normal and wide) manipulation conditions. SL manipulations yielded significant changes in mean anterior-posterior (AP) margins of stability (MOS(ap)) (p<0.0005) but not mediolateral (ML) margins of stability (MOS(ml)) (p≥0.0579). Taking wider steps increased mean MOS(ml) while decreasing MOS(ap) (p<0.0005). Walking with either wider or long steps, each of which increases the base of support, yielded increased AP and ML MOS variability (p≤0.0468). Step-to-step analysis of MOS(ml) indicated that subjects took stable steps followed immediately by stable steps. Overall, short-term, voluntary adoption of wider steps may help increase instantaneous lateral stability but shorter steps did not change lateral stability during unperturbed walking. We suggest that the observed changes in stability margins be considered in gait training programs which recommend short-term changes in step characteristics to improve stability.