Figure 5. Force–velocity relations in two slow fibres (A) and in two fast fibres (B). Negative velocity refers to lengthening.
Open symbols, steady force; filled circles, peak of force during lengthening. A, triangles (sf-1) and circles (sf-2) refer to the same slow fibres as in Fig. 4. B, triangles: 2A fast fibre (same fibre as in Fig. 3); circles: 2A/2X fast fibre (fibre length, 3.40 mm; segment length under the striation follower, 1.20 mm; average segment sarcomere length, 2.64 μm; CSA, 12 400 μm2; temperature, 11.6°C; isometric force, 170 kPa). Filled circles show the relation between the peak of force and the lengthening velocity during the corresponding phase of force response for the sf-2 and 2A/2X fibres.