Fig. 2. Simulation: effect of the phase shift . The fraction of the mechanical energy recovered through the pendular transduction in the simulation, calculated as R_step (dotted line, Equation 4) or as R_int (solid line, Equation 6) is plotted as a function of the phase shift between the curves E_p=-sinx and E_k=sin(x-) illustrated in Fig. 1. The two vertical continuous lines encompass the values of attained during all speeds of walking: decreases from approximately 45° at the lowest speeds to approximately -45° at highest speeds (Cavagna et al., 1983). The two vertical broken lines encompass the values of (10°-20°) observed in this study (Table 1). Note that R_stepR_int over the entire range of measured during walking.