Oxygen uptake kinetics in endurance-trained and untrained postmenopausal women

The rate of adjustment for pulmonary oxygen uptake (πV ̇ O_2p) is slower in untrained and in older adults. Near-infrared spectroscopy (NIRS) has shed light on potential mechanisms underlying this in young men and women and in older men; however, there is no such data available in older women. The purpose of this study was to gain a better understanding of the mechanisms of slower πV ̇ O_2p in older women who were either endurance-trained or untrained. Endurance-trained (n = 10; age, 62.6 ± 1.0 years) and untrained (n = 9; age, 69.1 ± 2.2 years) older women attended 2 maximal and 2 submaximal (90% of ventilatory threshold) exercise sessions. Oxygen uptake (V ̇ O₂) was measured breath by breath, using a mass spectrometer, and changes in deoxygenated hemoglobin concentration of the vastus lateralis ([HHb]) were measured using NIRS. Heart rate was measured continuously with a 3-lead electrocardiogram. V ̇ O_2p was faster in trained (35.1 ± 5.5 s) than in untrained (57.0 ± 8.1 s) women. The normalized [HHb] to V ̇ O₂ ratio, an indicator of muscle O₂ delivery to O₂ utilization, indicated a smaller overshoot in trained (1.09 ± 0.1) than in untrained (1.39 ± 0.1) women. Heart rate data indicated a faster adjustment of heart rate in trained (33.0 ± 13.0) than in untrained (68.7 ± 14.1) women. The pairing of V ̇ O_2p data with NIRS-derived [HHb] data indicates that endurance-trained older women likely have better matching of O₂ delivery to O₂ utilization than older untrained women during moderate-intensity exercise, leading to a more rapid adjustment of V ̇ O_2p.