Fig. 5. Cumulative metabolic cost over 10 contractions, derived from oxygen consumption as described in Materials and methods. `I', shortening contractions preceded by an isometric phase; `S', shortening contractions preceded by a stretch; `Isometric', cost of a 100 ms isometric contraction; `Stretch', cost of a 25 ms stretch followed by 75 ms isometric contraction. Cost is expressed relative to muscle mass. Values are means ± s.e.m. P values compare the measurements that they straddle using values uncorrected for muscle mass.