Fig. 2. Blood flow (mean ± s.e.m., N=6) to the muscles that showed significant changes in flow when guinea fowl carried a load on their backs equal to 23% of body mass. Open bars, control values for unloaded running at 1.5 m s^-1; shaded bars, the loaded values. Muscles are grouped into those active during swing and stance as indicated by EMG activity, previously measured during unloaded running. The FT is grouped with the stance muscles under the assumption that all of the increase in flow due to a trunk load is due to stance-phase metabolic activity (see text). Abbreviations are defined in Table 1.