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The adaptation of pulmonary oxygen uptake (V[O.sub.2p]) 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 V[O.sub.2p] kinetics, pyruvate dehydrogenase (PDH) activation, muscle metabolite contents, and muscle deoxygenation in older adults [n = 6; 70 [+ or -] 5 (67-74) yr] during moderate-intensity exercise ([Mod.sub.1]) and during moderate-intensity exercise preceded by heavy-intensity warm-up exercise ([Mod.sub.2]). The phase 2 V[O.sub.2p] time constant ([tau]V[O.sub.2p]) was reduced (P < 0.05) in [Mod.sub.2] (29 [+ of -] 5 s) compared with [Mod.sub.1] (39 [+ or -] 14 s). PDH activity was elevated (P < 0.05) at baseline prior to [Mod.sub.2] (2.1 [+ or -] 0.6 vs. 1.2 [+ or -] 0.3 mmol acetyl-CoA x [min-kg wet wt-l), 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 Mod2 compared with Modl. 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 02 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 O2 availability. V[O.sub/2] kinetics; ageing; pyruvate dehydrogenase; phosphocreatine