Fig. 4. (A) Data recordings of plantaris longus force (red), whole-muscle length (blue), and activation (black) from frog 4 to show the maximum differences observed between individual animals (compare with Fig. 3A). (B) Diagram showing the variation in the relative timing of force–length activation events among swimming strokes for frog 5. Note that force develops passively at the end of the previous cycle, as the limb is being protracted and the ankle and knee are flexed.