Simulating Ideal Assistive Devices to Reduce the Metabolic Cost of Running
Flexion/extension actuators were added bilaterally at the ankle (A), knee (K), and/or hip (H). The mean (column) and standard deviation (vertical line) over 10 subjects are shown for seven assistance scenarios when running at 2 m/s (left) and 5 m/s (right). The hatched regions approximate the change in average metabolic power attributable to unidirectional (i.e., only flexion or only extension) assistive torques. Change in metabolic cost is reported as power averaged over the gait cycle and normalized by subject mass (vertical axis), and as a percentage (indicated below each column); both quantities are expressed relative to the average metabolic power consumed in the unassisted simulations at each speed. When running at 2 m/s, the three actuators were approximately equally effective when used separately; when running at 5 m/s, the hip actuator was significantly more effective than the ankle or knee actuators (p < 0.002, matched pairs t-test).