Fig. 2. Representative electromyograms from a trout swimming steadily in uniform flow at three speeds, along with the corresponding lateral (z-axis) excursions of the center of mass (COM; gray circles). At a flow speed approximating the reduced velocity behind the cylinder (A), only the posterior red muscles are active. At a flow speed of 3.5 L s^–1 (B), there is a propagating wave of red muscle activity down the entire body with no white muscle activity. When trout swam at the highest speed (C), anaerobic white muscles were recruited. At each swimming speed, staggered onset times of muscle activity down the body reflect the presence of a propulsive body wave. Scale bars for time (black, horizontal), electromyography intensity (black, vertical) and COM amplitude (gray) are shown.