Fig. 3. Muscle force and fascicle length for the lateral gastrocnemius (LG) and peroneus longus (PL) muscles in three turkeys running at a steady speed of 2 m s^–1 on level ground. Shaded areas are stance; unshaded areas are swing. Force–length relationships for the LG and PL over one complete stride (swing and stance) are also shown for each bird. Arrows in a counterclockwise direction indicate net positive work in the work loop. Arrows for PL at the start of stance indicate a small fraction of active lengthening performed in the stretch–shorten cycle. L, fascicle length; L₀, resting segment length.