EVALUATION OF MUSCLE OXIDATIVE POTENTIAL BY P-31-MRS DURING INCREMENTAL EXERCISE IN OLD AND YOUNG HUMANS

The purpose of this study was to compare muscle oxidative capacity bet ween moderately active young and old humans by measuring intracellular threshold (IT) during exercise with P-31-magnetic resonance spectrosc opy (P-31-MRS). Changes in phosphocreatine, inorganic phosphate, and i ntracellular pH were measured by P-31-MRS during a progressive unilate ral ankle plantar flexion exercise protocol in groups of moderately ac tive old (n = 12, mean age 66.7 years) and young (n = 13, mean age 26. 2 years) individuals. From muscle biopsy samples of the lateral gastro cnemius, citrate synthase (CS) activity was determined in six subjects from each group, and fibre type composition was determined in nine ol d and ten young subjects. The old group had a lower IT for pH, as a pe rcentage of peak work rate (P < 0.05), despite a similar CS activity c ompared to the young. IT was significantly correlated with CS activity (R = 0.59; P < 0.05), but not with fibre type composition. It was con cluded that metabolic responses to exercise are affected by ageing, as indicated by a lower IT in old compared to young individuals.