Fig. 4. Examples of work loops. (A) The duration of the initial isometric contraction was 10 % of the cycle duration, and the amplitude of shortening was 5 % L_max (solid line), 10 % L_max (dashed line) or 15 % L_max (dotted line), where L_max is the length at which active force production is maximal. The duration of the lengthening phase was constant. Therefore, the velocity of shortening increased as the amplitude of shortening increased. (B) The amplitude of shortening was 10 % L_max and the duration of the lengthening phase was 50 % of the cycle duration. The duration of the initial isometric phase was 10 % (solid line), 15 % (dashed line) or 20 % (dotted line) of the cycle duration. Time progressed around the loops in an anticlockwise direction, indicating that net work was performed. Length, change in muscle length.