Analysis of sloped gait: How many steps are needed to reach steady-state walking speed after gait initiation?

Abstract

Background: Gait initiation in level walking is suggested to take three steps before reaching steady-state walking speed. In sloped gait, it is not clear if the general recommendation of level gait can be used.

Research question: The aim of this study was to investigate (1) if steady-state walking speed is reached within four steps in sloped gait, and (2) to what extent the number of initial steps cause differences in step length, cadence and ground reaction force (GRF).

Methods: Fourteen healthy participants walked on an instrumented ramp at inclinations of 0°, ±6°, ±12°, and ±18°, covering slight (clinical application) to steep (hiking and mountaineering) slopes. The starting position on the ramp was adjusted to collect each of the first to fourth step using a 12 infrared-camera motion capture system and two force plates. For each slope condition steady-state walking speed was determined using the ratio of the braking and propulsion impulse (ratio p_ap;p_brakingp_propulsion) and the resultant Centre of Mass (CoM) speed (vel_CoM). Statistical differences between steps were calculated by using a Friedman ANOVA and pairwise post-hoc Wilcoxon tests.

Results: In all inclinations, ≥90 % (uphill) and ≥95 % (downhill) of steady-state speed regarding ratio p_ap and maximum vel_CoM was reached with the 3rd step. In the level and uphill condition the 4th step showed a slight decrease in vel_CoM. In uphill and downhill condition, the acceleration was mainly generated due to the increase in cadence with significant increases between the 1st and 2nd step as well as between the 2nd and 3rd step. A significant increase in step length was only observed in the uphill conditions.

Significance: Steady-state walking speed was reached with the 3rd step and thus, walkways which allow for two initial steps seem to be appropriate for uphill and downhill gait analysis for inclinations up to ±18°.

Keywords: Centre of mass speed; Downhill gait; Ramp inclination; Sloped gait; Uphill gait.