Control strategies for initiation of human gait are influenced by accuracy constraints

The accuracy of placement of swing limb heel-strike was used to determine strategies of motor control of the stance limb during gait initiation (GI). Subjects initiated gait as fast as possible with the swing limb heel-strike landing on either a small or large target. Stance limb ground reaction forces, electromyogram duration and temporal data for GI were measured. It was hypothesized that accuracy would affect movement speed and the rate of rise, or the slope, of the ground reaction forces that control GI. The slopes of the stance limb forces that coincide with swing limb toe-off remained invariant. However, the slopes of forces and peak forces related to swing limb heel-strike were significantly less for the small target. These initial data suggest that principles of upper extremity motor control may be generalized to the initiation of movement from upright stance.