Simulating Ideal Assistive Devices to Reduce the Metabolic Cost of Running
Mean activations are shown for three uniarticular muscles on the posterior side of the right leg (left column), three uniarticular muscles on the anterior side of the leg (right column), and three biarticular muscles (center column) in four scenarios: unassisted (black) and when assisted by ideal hip (red), knee (green), or ankle (blue) flexion/extension actuators. Note that the vastus lateralis and rectus femoris insert into the patella (not shown in the diagram at right), thereby allowing them to generate knee extension moments. Ankle and knee actuators dramatically reduced activations of uniarticular muscles crossing the ankle and knee, respectively; the effect of the hip flexion/extension actuator was unique, in part, because the hip joint has two additional degrees of freedom. When knee or hip actuators were added, the rectus femoris activation increased in some parts of the gait cycle to take advantage of its relatively high force-generating capacity.