Fig. 5. Muscle power as a function of strain. Each symbol represents a different animal. The closed green symbols represent muscle 177c. Muscle 177c always generated power when operating over a range of strain amplitudes near its in vivo strain (7 %). The open red symbols represent muscle 179. Muscle 179 always absorbed energy when operating over a range of strain amplitudes near its in vivo running strain (16.4 %). Muscle function was not sensitive to strain excursion (or joint angle amplitude) when operating under otherwise in vivo running conditions.