Simulating Ideal Assistive Devices to Reduce the Metabolic Cost of Running
(a) The average metabolic power consumed by the two muscles whose energy consumption decreased the most (vasti and biceps femoris short head) and by the iliopsoas and rectus femoris, whose energy consumption decreased and increased, respectively. (b) Mean hip (top) and knee (bottom) flexion moments are shown for the right leg when unassisted (dashed lines) and when assisted by an ideal knee actuator (solid lines), averaged across 10 subjects; the mean knee actuator torque from Fig 3 is shown for reference (black). The rectus femoris had a higher force-generating capacity than the iliopsoas during early swing because the rectus femoris muscle fibers were lengthening while those of the iliopsoas were shortening. Thus, the recruitment of the rectus femoris increased to generate more of the necessary hip flexion moment, and the superfluous knee extension moment it generated was neutralized by the ideal actuator.