Fig. 5. Effects of varying the shortening amplitude (%L_max, where L_max is the length at which active force production is maximal) and the duration of isometric contraction (percentage cycle duration) on mean work output per cycle (A), enthalpy output per cycle (B) and net mechanical efficiency, _Net (C). The duration of isometric contraction was 10 % (black columns), 15 % (white columns) or 20 % (grey columns) of the cycle duration. Letters indicate statistically significant differences between variables attributable to the duration of isometric contraction. Asterisks indicate statistical significance, at a particular isometric duration, attributable to shortening amplitude. Values are means + S.E.M., N=7.