Fig. 4. A comparison of the movement of the body (thick black lines) with the shortening of the plantaris muscle fascicles (thin red lines) in two frog jumps (frog 1 and frog 6). The velocity of shortening in the plantaris is independent of the velocity of the body (A,C). Panels B and D contrast the shortening of the plantaris muscle fascicles with the displacement of the body. At the point where half of the muscle fascicle shortening has occurred (vertical broken line), the body has undergone very little displacement. EMG, electromyographic activity.