Fig. 6. Normalized, average rectified electromyograms of anterior (R1) and posterior (R4) red muscle activity (solid black line) along with the upper limit of the S.E.M. (solid gray line) for all five trout swimming in uniform flow (A and C; n=20) and Kármán gaiting (B and D; n=14). Data are shown relative to one oscillation cycle of the center of mass (COM; gray circles). Mean onset and offset times of muscle activity (horizontal gray bar) along with their S.E.M. are shown above each graph, where applicable. When trout are behind the cylinder (B), R1 onset and offset times (vertical broken lines) occur relatively earlier in the COM cycle than for trout swimming in uniform flow (A). (C) Rectified area for R4 during swimming in uniform flow (n=20) shows delayed onset and offset times relative to A, indicating the presence of a propagating body wave. (D) By contrast, no posterior red muscle activity is present when trout Kármán gait.