Relationship between pulmonary O2 uptake kinetics and muscle deoxygenation during moderate-intensity exercise

1 Canadian Centre for Activity and Aging, 2 School of Kinesiology, and 3 Department of Physiology and Pharmacology, The University of Western Ontario, London, Ontario, Canada N6A 3K7 Submitted 15 October 2002 ; accepted in final form 27 March 2003 The temporal relationship between the kinetics of phase 2 pulmonary O 2 uptake ( O 2p ) and deoxygenation of the vastus lateralis muscle was examined during moderate-intensity leg-cycling exercise. Young adults (5 men, 6 women; 23 ± 3 yr; mean ± 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 O 2p 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). O 2p data were filtered, interpolated to 1 s, and averaged to 5-s bins; HHb data were averaged to 5-s bins. Phase 2 O 2p 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 O 2p (30 ± 8 s) was slower ( P < 0.01) than that for HHb (10 ± 3 s). The TD HHb before an increase in HHb was 13 ± 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 O 2 utilization. After this initial TD HHb , the kinetics of local muscle deoxygenation were faster than those of phase 2 O 2p (and presumably muscle O 2 consumption), reflecting increased O 2 extraction and a mismatch between local muscle O 2 consumption and perfusion. near-infrared spectroscopy; muscle oxygen utilization Address for reprint requests and other correspondence: D. H. Paterson, Canadian Centre for Activity and Aging, School of Kinesiology, The Univ. of Western Ontario, London, Ontario, Canada N6A 3K7 (E-mail: dpaterso{at}uwo.ca ).