Figure 9.

Comparison of the gaits produced by the bi-articular spring model and by humans. (a) Human kinematics, shown as angles of stance leg, swing thigh and swing shank measured anticlockwise with respect to vertical (data from Winter 1991). Stance leg angle (solid line) is defined as the average of the thigh and shank (dotted lines) for comparison with model. (b) Bi-articular model kinematics (from figure 8c, gait requiring minimum spring force). One difference with humans is that the model's stance leg is fully extended at double support, leading to different initial conditions for the swing phase and less swing phase knee flexion. (c) Knee torque versus hip torque for human and model, emphasizing swing phase. Human swing phase has joint torques covarying fairly linearly. In the model, linear covariation is a result of the bi-articular springs, although the average ratio of knee and hip torques is somewhat lower (−0.33 versus approximately −0.68 in humans). The dynamic walking model is powered by push-off, and bi-articular springs allow it to walk at the equivalent of a human's 1.25 m s⁻¹.