Fig. 1. Representative organismal oxygen consumption of a guinea fowl during rest and during level running (circles) and incline running (triangles) over a range of speeds. The bird was initially tested running at 1.5 m s^–1 on the level and 1.5 m s^–1 on a 15% gradient. Subsequent measurements were made over a range of faster running speeds (2.0–3.0 m s^–1) in order to determine the speed for which the organismal oxygen consumption matched that at 1.5 m s^–1 and 15% gradient (as indicated by arrows). Lines were fitted by eye to illustrate the experimental design.