Experimental V’O2 and simulated muscle V’O2, metabolite concentrations and ATP usage/supply fluxes during low-intensity (baseline) and high-intensity cycling exercise in untrained and trained muscle.

(A) Experimental and simulated V’O2, simulated ADP and pH. (B) Simulated PCr, Pi and ATP. (C) Simulated ATP usage (UT), ATP supply by OXPHOS (OX), ATP supply by anaerobic glycolysis (GL), ATP supply by creatine kinase (CK). Experimental baseline-heavy-intensity exercise transition: after 3 min. Simulated baseline-heavy-intensity exercise transition: after 3.4 min (the delay by 24 s corresponds to the cardio-dynamic phase of the pulmonary V’O2 on-kinetics). The muscle V’O2 is calculated based on the assumption that during baseline-intensity exercise (20 W) muscle V’O2 constitutes ~75% and during heavy-intensity exercise ~85% of the pulmonary V’O2 (see Ref. [40]).