IMPROVEMENT OF MUSCULAR OXIDATIVE CAPACITY BY TRAINING IS ASSOCIATED WITH SLIGHT ACIDOSIS AND ATD DEPLETION IN EXERCISING MUSCLES

Metabolic and mechanical properties of female rat skeletal muscles, su bmitted to endurance training on a treadmill, were studied by a 60-min in vivo multistep fatigue test, P-31-NMR was used to follow energy me tabolism and pH, Mechanical performance was greatly improved in traine d muscles, The oxidative capacity of the skeletal muscles was evaluate d from the relationship between ADP calculated from the creatine kinas e equilibrium and work and from the measure of the rate of phosphocrea tine (PCr) resynthesis following exercise, In trained muscles, ADP pro duction was lower per unit of mechanical performance, showing an impro vement of oxidative metabolism, However, the PCr resynthesis rate was not modified, Slight acidosis and ATP depletion were observed from the beginning of the fatigue test, These modifications suggest changes of the creatine kinase equilibrium favoring mitochondrial ATP production , Our results indicate that muscle status improvement could be accompa nied by ATP depletion and minimal acidosis during contraction; this wo uld be of particular importance for objective evaluation of muscle reg eneration processes and of gene therapy in muscle diseases. (C) 1996 J ohn Wiley & Sons, Inc.