Prior heavy exercise elevates pyruvate dehydrogenase activity and muscle oxygenation and speeds O2 uptake kinetics during moderate exercise in older adults.

The adaptation of pulmonary oxygen uptake (VO2p) kinetics during the transition to moderate-intensity exercise is slowed in older compared with younger adults; however, this response is faster following a prior bout of heavy-intensity exercise. We have examined VO2p kinetics, pyruvate dehydrogenase (PDH) activation, muscle metabolite contents, and muscle deoxygenation in older adults In = 6; 70 ± 5 (67-74) yr] during moderate-intensity exercise (Mod1) and during moderate-intensity exercise preceded by heavy-intensity warm-up exercise (Mod2). The phase 2 VO2p time constant (τVO2p) was reduced (P < 0.05) in Mod2 (29 ± 5 s) compared with Mod1 (39 ± 14 s). PDH activity was elevated (P < 0.05) at baseline prior to Mod2 (2.1 ± 0.6 vs. 1.2 ± 0.3 mmol acetyl-CoA∙min-1∙kg wet wt-1), and the delay in attaining end-exercise activity was abolished. Phosphocreatine breakdown during exercise was reduced (P < 0.05) at both 30 s and 6 mm in Mod2 compared with Mod1. Near-infrared spectroscopyderived indices of muscle oxygenation were elevated both prior to and throughout Mod2, while muscle deoxygenation kinetics were not different between exercise bouts consistent with elevated perfusion and O2 availability. These results suggest that in older adults, faster VO2p kinetics following prior heavy-intensity exercise are likely a result of prior activation of mitochondrial enzyme activity in combination with elevated muscle perfusion and 02 availability. [ABSTRACT FROM AUTHOR]