Fig. 1. An example of records, averaged over the last 10 cycles (4.54 s) of the contraction protocol, from one papillary muscle (mass, 3.1 mg; L_max, 5.9 mm). Stimulus was applied at 0 ms. (A) Change in muscle length. The muscle was initially held isometric, was then allowed to shorten at constant velocity through an amplitude of 10% L_max and was then lengthened at constant velocity. (B) Absolute force output. The horizontal broken line indicates the passive force at L_max. The force was lower after shortening because the passive force was lower at the short length. The muscle was relaxed during most of the lengthening phase. (C) Time course of work output and total enthalpy output (work + heat). The vertical broken line indicates the time at which shortening ended.