Skeletal Muscle O2 Availability Regulates Myoglobin And Phosphocreatine Recovery Following Exercise In Humans

Abstract

Oxygen has been implicated in the regulation and limitation of skeletal muscle metabolism. However, there are limited data directly assessing intracellular oxygenation and metabolism in humans. PURPOSE To determine the relative time course (τ) of myoglobin (Mb) and phosphocreatine (PCr) recovery and the impact of varied concentration of inspired oxygen (FIO2) upon high intensity exercise. METHODS Six healthy subjects with wide-ranging fitness levels performed high intensity plantar flexion exercise; onset, steady-state, and offset kinetics were assessed during hypoxic (10% FIO2), normoxic (21% FIO2), and hyperoxic (100% FIO2) conditions. Using a 4-Tesla superconducting magnet, intracellular oxygenation (1H deoxyMb spectroscopy), and energy metabolism (31P spectroscopy) were evaluated simultaneously using a rapid interleaved NMR sequence. RESULTS Following exercise, the time constant for Mb reoxygenation (τMb) increased progressively as a function of FIO2 (hyperoxia = 8.9 ± 3.9s, normoxia = 15.4 ± 6.9s, hypoxia = 17 ± 7.6s). The time constant for PCr recovery (± PCr) was delayed compared to τMb, and was clearly dependant upon O2 availability (hyperoxia = 25.9 ± 11.6s, normoxia = 28.2 ± 12.6s, hypoxia = 52.5 ± 8.5s). CONCLUSION These data document O2-dependant, rapid reoxygenation kinetics following exercise that precede rephosphorylation, emphasizing the important effect of O2 availability on metabolism in human skeletal muscle. Funded by NIH HL-17731 and Association Française contre les Myopathies grants (AFM).