Fig. 2. (A) Diagram of the experimental apparatus used. (B) Changes in torque over time during a simulated cycle of joint movement. Elastic mechanisms resist flexion (Input impulse) but assist extension (Output impulse), the difference representing entropic energy loss. (C) Changes in torque over the range of joint angles used during locomotion. The area under the upper (loading) curve represents input energy; the area under the lower (unloading) curve represents output energy; the difference between them represents lost energy. Output energy divided by input energy multiplied by 100 is the percent efficiency or resilience.