Fig. 4.

Effects of swing phase vibration. A: group average mediolateral locations of the sacrum and both heels are illustrated over 6 consecutive steps, as in Fig. 3. Again, any effects of the applied vibration are subtle. B: effects of swing phase vibration did not reach the level of significance for mediolateral foot placement for left steps (P = 0.067) but significantly influenced right steps (P = 0.008). C: vibration significantly influenced sacrum displacement for both left (P < 0.0001) and right (P = 0.004) steps. D: vibration had a significant effect on step width for left steps (P = 0.0008) but not right steps (P = 0.65). E: vibration had a significant effect on estimated margin of stability for both left steps (P = 0.007) and right steps (P = 0.003). F: vibration had a significant main effect (P = 0.023) on left step periods, but no post hoc comparisons reached the level of statistical significance. Vibration did not influence right step period (P = 0.11). G: vibration did not significantly influence left step length (P = 0.43) or right step length (P = 0.55). For B–G, all data are plotted as the change from the unperturbed steps prior to the vibration, and error bars represent standard deviation. The shaded boxes indicate the steps during which the perturbation was applied. The top rows in B–G represent left steps, and the bottom rows represents right steps. *Steps that are significantly different from the unperturbed step with this leg (post hoc test; P < 0.05), with estimated ES indicated.