Fig. 3. Expanded and averaged recordings of muscle length, force and electromyographic (EMG) activity from the lateral gastrocnemius (LG, above) and digital flexor-4 (DF-IV, below), normalized to a single stride. The support phase of the stride is shaded in gray. Results are shown for bird 4, running at 1.3 m s^-1 on the level (left), and at 16° incline (right). The traces of force and length are means ± S.D. obtained from 10 strides, and a single EMG trace is shown for reference. The error bars below the EMG traces indicate the mean ± S.D. for the timing of EMG activity (onset, offset).