Analysis of Ground Reaction Force Impulses During Uneven Walking for Young and Older Adults

Humans navigate various terrains by exerting forces to direct the Center of Mass (COM) and maintain balance. During walking, humans transition from one stance leg to the next by exerting impulses during the step-to-step transition. Studying these transition impulses may provide insight into how humans traverse uneven terrains. When walking speed increased (constant terrain amplitude), the average braking and propulsive impulses (posterior/anterior) increased comparably (-0.0270 m {middle dot} s-1 {middle dot} g-1 v-1versus 0.0252 m s-1{middle dot} g-1 v-1). In the vertical direction, while the collision impulse remained constant, the push-off impulse declined by -0.0535 m {middle dot} s-1 {middle dot} g-1 {middle dot} v-1. The interaction of age and speed also increased the collision impulse (0.0202 m {middle dot} s-1 {middle dot} g-1 {middle dot} v-1). With the rise of terrain amplitude (constant speed), the braking and propulsive impulses rose by -0.0607 m {middle dot} s-1 {middle dot} g-1 {middle dot} m-1 and 0.0701 m {middle dot} s-1 {middle dot} g-1 {middle dot} m-1, respectively. Thus, we could infer that the propulsive impulse also contributed to the gait mechanical energy. While the collision impulse increased with terrain amplitude (0.1775 m {middle dot} s-1 {middle dot} g-1 {middle dot} m-1) and the interaction of age and terrain amplitude (0.1058 m {middle dot} s-1 {middle dot} g-1 {middle dot} m-1), the push-off impulse declined (-0.2700 m {middle dot} s-1 {middle dot} g-1 {middle dot} m-1 and -0.1473 m {middle dot} s-1 {middle dot} g-1 {middle dot} m-1). We also observed the push-off as a fraction of the total vertical impulse declined. Therefore, we detected a mechanical energy deficit in the step-to-step transition that must have been compensated for during the mid-flight phase. Considering the portion of push-off occurring after the subsequent heel-strike as delayed push-off, while it increased with walking speed, it declined with terrain amplitude. Thus, during uneven walking, the push-off exertion must have been interrupted, indicating the demand for further mechanical energy infusion after the transition.