Fig. 5.
Operating range of young and old muscles under three simulation conditions, mapped on experimentally derived force-length and force-velocity curves: simulation I, young; simulation II, old, strain-matched conditions; simulation III, old, force-matched conditions. Data are shown only for the active portion of the cycle. A: young and old muscle acting under the same strain stretch-shorten conditions (muscle Linitial = 1.1L0, 25% MTU strain) operate on the descending limb of the force-length curve. However, old muscle acting under conditions that match the MTU passive force produced during stretching operate on the plateau, nearer to L0. B: young muscle operates over a broader range of velocities than old muscle under either strain-matched or force-matched condition.