Effect of Overload on Anticipatory Control of Gait Initiation

It is accepted that the role of Anticipatory Postural Adjustments (APA) during gait initiation is to create the propulsive forces necessary to reach the gait velocity at the end of the first step. The aim of this study was to examine whether and how an overload modifies these APA. Twenty-one subjects performed gait initiation in two experimental conditions: unloaded (UL) and with an overload of 15% body mass (WL). In each condition, two speed conditions were imposed: Normal and Fast. The results showed that the subjects maintained a similar gait velocity at the end of first step with the overload whatever the speed condition. For that, in normal speed condition, they increased the duration of APA with the overload. By increasing the duration of this phase, the subjects maintained the same horizontal CG velocity at heel-off. However, when the gait speed was faster, the duration of APA could not be increased, and therefore the CG velocity at heel-off decreased with the overload. To maintain the gait velocity in fast speed condition, the subjects had to compensate the lacking of initial velocity by lengthening the step execution duration. In conclusion, to maintain a similar gait velocity, overloaded individuals must increase the duration of APA, but if the APA cannot be increased, they use another strategy that consists to increase the duration of the step execution phase.