DeLorey, Darren S., John M. Kowalchuk, and Donald H. Paterson. Relationship between pulmonary O 2 uptake kinetics and muscle deoxygenation during moderate-intensity exercise. J Appl Physiol 95: 113-120, 2003. First published April 4, 2003 10.1152/japplphysiol.00956.2002The temporal relationship between the kinetics of phase 2 pulmonary O 2 uptake (V O2p) and deoxygenation of the vastus lateralis muscle was examined during moderate-intensity leg-cycling exercise. Young adults (5 men, 6 women; 23

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... Ϯ 3 yr; mean Ϯ SD) performed repeated transitions on 3 separate days from 20 W to a constant work rate corresponding to 80% of lactate threshold. Breath-by-breath V O2p was measured by mass spectrometer and volume turbine. Deoxyhemoglobin (HHb), oxyhemoglobin, and total hemoglobin and myoglobin were sampled each second by near-infrared spectroscopy (Hamamatsu NIRO-300). V O2p data were filtered, interpolated to 1 s, and averaged to 5-s bins; HHb data were averaged to 5-s bins. Phase 2 V O2p data were fit with a monoexponential model. For HHb, a time delay (TD HHb) from exercise onset to an increase in HHb was determined, and thereafter data were fit with a monoexponential model. The time constant for V O2p (30 Ϯ 8 s) was slower (P Ͻ 0.01) than that for HHb (10 Ϯ 3 s). The TD HHb before an increase in HHb was 13 Ϯ 2 s. The possible mechanisms of the TD HHb are discussed with reference to metabolic activation and matching of local muscle O 2 delivery and O2 utilization. After this initial TD HHb, the kinetics of local muscle deoxygenation were faster than those of phase 2 V O2p (and presumably muscle O 2 consumption), reflecting increased O2 extraction and a mismatch between local muscle O 2 consumption and perfusion. near-infrared spectroscopy; muscle oxygen utilization