Prior heavy exercise elevates pyruvate dehydrogenase activity and muscle oxygenation and speeds O2uptake kinetics during moderate exercise in older adults

Abstract

The adaptation of pulmonary oxygen uptake (V̇o2p) 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 V̇o2pkinetics, pyruvate dehydrogenase (PDH) activation, muscle metabolite contents, and muscle deoxygenation in older adults [ n = 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 V̇o2ptime constant (τV̇o2p) 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 min in Mod2compared with Mod1. Near-infrared spectroscopy-derived 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 O2availability. These results suggest that in older adults, faster V̇o2pkinetics following prior heavy-intensity exercise are likely a result of prior activation of mitochondrial enzyme activity in combination with elevated muscle perfusion and O2availability.