Fig. 1. Examples of muscle length changes (Length) during realistic contraction protocols at 2 Hz. A, B and C show the length change protocols for experiment 1 and D for experiment 2. In A, the duration of initial isometric contraction was 10, 15 or 20 % of the total inter-stimulus interval (0.5 s) (shown for 10 % L_max shortening only), where L_max is the length at which active force production is maximal. In B, the isometric phase was substituted by a 2 or 4 % L_max length increase, accounting for 15 % of the cycle duration. At each isometric duration, the muscle was shortened by 5, 10 or 15 % L_max (shown for an isometric duration of 15 % of the cycle only) (C). The duration of the lengthening phase was kept at 50 % of the cycle duration in A, B and C. In D, isometric phase duration was 20 % of the cycle duration, while shortening was for 20, 30 or 40 % of the inter-stimulus interval. The duration of the lengthening phase was adjusted accordingly. Shortening amplitude was 10 % L_max in B and D. The stimulus pulse was applied at time zero.