Meeting Abstract
Conventionally, all or nearly all of the mechanical cost of bipedal walking is assumed to be incurred during the step-to-step transition, whereas the single stance or ‘vaulting’ phase is assumed to be free of cost. We investigate human walking dynamics using mechanical cost analysis (MCA) to analyze single stance (SS) and double stance (DS) periods of the stride separately. This strategy determines the contribution of SS and DS dynamics to the mechanical cost of transport (CoTmech) for a single stride. We test the effect of walking speed on SS and DS mechanical cost dynamics in nine healthy adults.
Our experimental results show collision angles of 0.07 in DS and 0.05 radians in SS, indicating that the dynamics of DS are more costly than those of SS. As walking speed increases, collision angles remain relatively constant, force angles increase in both DS and SS, and velocity angles increase in SS and decrease in DS. Increasing force angles are consistent with greater step lengths during faster walking. Velocity angles increase by 22% in SS, due to longer steps, but decrease by 31% in DS as walking speed increases. Decreasing velocity angles during DS indicate that redirection of the CoM from down to up happens more quickly and has a flatter trajectory as walking speed increases. Collision angles, and thus CoTmech, remain relatively constant across the speed range considered.
With increased walking speed, the collision fraction – a ratio of the actual collisions to the potential collisions – remains relatively constant during DS, but this fraction is reduced by 24% during SS. This means that the dynamics of the step-to-step transition remain similar, regardless of speed. In contrast, collisions are mitigated more effectively during SS at faster walking speeds. A key finding of this work is that mechanical cost is not relegated to just the step-to-step transition.
