Simulated dynamics and experimental data for intracellular species concentrations in skeletal muscle in response to an increased work rate equivalent to cycle ergometer exercise at 50% VO2max for subjects corresponding to Experiment 1: (A) Glycogen, (B) Phosphocreatine (PCr), (C) Lactate in tissue; (D) Glycogen, (E) PCr and (F) ATP in type I and II fibers; (G) Respiratory quotient (RQ); (H) Oxygen Uptake; (I) Plasma Lactate; (J) Effective volume change of whole muscle, type I and II fibers and blood domain; (K) Citrate Synthase flux; (L) β oxidation contribution to the citrate synthase flux. The lines represent model simulations of whole muscle (—), type I fibers (---) and type II fibers (. . .). Experimental data are means ± standard error. Solid squares for whole tissue; upper triangles for type I fibers; diamonds for type II fibers.