Fig. 4. Representative strain, total stress and power when muscles 178 and 179 operated under identical strain and stimulation conditions. The shaded area represents the shortening phase of the oscillatory cycle. The stimulation pattern, represented on the graphs by the yellow squares, was determined during running at the animal's preferred speed (3 pulses at 100 Hz) (Full et al., 1998; Ahn and Full, 2002). (A) The strain pattern was identical for both muscles (15% strain amplitude). (B) Muscle stress during imposed running conditions. The shaded areas represent the shortening (or stance) phase of the oscillatory cycle. (C) Work loops for muscles 178 and 179 under identical conditions. Work loops show muscle 178 generated net mechanical power during the cycle, while muscle 179 absorbed net mechanical power under identical conditions. Arrows indicate the direction of the loops.