Fig. 5. (A) Three superimposed recordings of active force during tetanic stimulation of a red fibre bundle shortening at different velocities. (B,C) Force and length change (L) on an expanded time scale. The horizontal lines in B show the forces that were measured during the period at the start of the ramp shortening when force was relatively constant. L₀, the fibre length at which maximum isometric force was produced, was 6.6 mm.