Figure 3.

Swing and stance contributions to intact-joint work loops. We separated the stance and swing components of a typical stride work loop (left column). Red and blue regions in the work loop traces (right plots) indicate respective regions of positive or negative incremental work (joint torque × angular displacement in (b) and (d), or muscle stress × strain in (f)). Incremental work was positive from one sampled point to the next, if the muscle shortened with positive stress or lengthened with negative stress. Net work was negative as evidenced by the clockwise stress–strain curves. The (a) top plots show the passive energy absorption of the joint under a typical strain pattern (figure 1b(ii)). Positive work was due to spring-like return of energy. (b) Active work loops with the typical two MAPs (figure 1a(iv)) produced significantly more positive and negative work (p < 0.01). Removing the passive joint work ((e); subtract (a) from (c)) isolated the effects of the ventral femoral extensor's activation on joint work. Reference length is measured following Full et al. [11].