Figure 4.

The effect of operating length on the peak force production in a muscle. Using an in vitro protocol we show the same muscle undergoing two contractions (1 and 2) where the fascicles shorten by about 30 per cent. (a) Operating lengths for two ‘fixed-end’ contractions in the same muscle shortening against elastic structures in vitro. In both contractions the muscle shortens by about 30 per cent, but contraction (1) starts on the plateau, while contraction (2) starts on the descending limb. The classic Gordon Huxley & Julian (1966) force–length curve illustrates the hypothetical effect of length on force for maximally activated, isometric muscle. (b) Developed force versus time for two sample contractions consisting of length changes depicted in panel (a). Higher peak force is developed when the muscle starts at a longer length. This example shows that peak force production may be influenced more by a muscle's length at the end of a contraction than by its initial length.