Fig. 1. Maximum aerobic capacity (_O2max) measured during forced exercise in a hypoxic (14% O₂), normoxic (21% O₂) and hyperoxic atmosphere (30% O₂) for 59 mice from lines selected for high voluntary wheel running (S) and their non-selected control lines (C). Each point represents the highest 60-s average obtained in two measurements on the treadmill performed on consecutive days (see Materials and methods). (Left panels) Aerobic capacity in relation to selection history - i.e. S (closed circles) versus C (open circles). Adjusted means for S and C in each P_O2 are listed in Table 2. (Right panels) The same graph, but highlighting individuals with the mini-muscle phenotype (all in S lines) versus normal phenotypes. Effects of size, selection history and mini-muscle are summarized in Table 2.