Figure 5.

Change in muscle fibre work caused by each step perturbation (circles) with respect to the reference hopping condition. ∆E_P (light blue) is the amount of work adjustment required to reject, within the preflex duration, the potential energy change caused by each step perturbation. ∆W_CE (green) is the net change in muscle fibre work. ∆$W_{\mathit{CE}}^V$ (dark blue) is the change in muscle fibre work induced by the force–velocity relation; ∆$W_{\mathit{CE}}^L$ (red) by the force–length relation; ∆$W_{\mathit{CE}}^A$ (yellow) by the muscle excitation. (a) Preflex-Const and (b) Preflex-Rising.