Fig. 4. Stance net mechanical work output for the lateral gastrocnemius (LG) and peroneus longus (PL) muscles during steady speed running at 1–3 m s^–1 on the level (open circles), 12° incline (filled triangles) and 12° decline (filled squares). Values are means ± S.E.M.; N=5 birds for the LG and N=4 for the PL; numbers above a symbol indicate a different number of birds at that speed. Across a range of running speeds, both the LG and PL performed greater net positive work in stance during incline versus level running, and they developed net negative work in stance during decline running.