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Adaptation of pulmonary O₂ uptake kinetics and muscle deoxygenation at the onset of heavy-intensity exercise in young and older adults

¹Canadian Centre for Activity and Aging, ²School of Kinesiology, and ³Department of Physiology and Pharmacology, The University of Western Ontario, London, Ontario, Canada

Submitted 14 June 2004 ; accepted in final form 5 January 2005

The purpose was to examine the adaptation of pulmonary O₂ uptake (O_2p) and deoxygenation of the vastus lateralis muscle at the onset of heavy-intensity, constant-load cycling exercise in young (Y; 24 ± 4 yr; mean ± SD; n = 5) and older (O; 68 ± 3 yr; n = 6) adults. Subjects performed repeated transitions on 4 separate days from 20 W to a work rate corresponding to heavy-intensity exercise. O_2p was measured breath by breath. The concentration changes in oxyhemoglobin, deoxyhemoglobin (HHb), and total hemoglobin/myoglobin were determined by near-infrared spectroscopy (Hamamatsu NIRO-300). O_2p data were filtered, interpolated to 1 s, and averaged to 5-s bins. HHb-near-infrared spectroscopy data were filtered and averaged to 5-s bins. A monoexponential model was used to fit O_2p [phase 2, time constant () of O_2p] and HHb [following the time delay (TD) from exercise onset to the start of an increase in HHb] data. The O_2p was slower (P < 0.001) in O (49 ± 8 s) than Y (29 ± 4 s). The HHb TD was similar in O (8 ± 3 s) and Y (7 ± 1 s); however, the HHb following TD was faster (P < 0.05) in O (8 ± 2 s) than Y (14 ± 2 s). The slower O_2p kinetics and faster muscle deoxygenation in O compared with Y during heavy-intensity exercise imply that the kinetics of muscle perfusion are slowed relatively more than those of O_2p in O. This suggests that the slowed O_2p kinetics in O may be a consequence of a slower adaptation of local muscle blood flow relative to that in Y.

near-infrared spectroscopy; muscle O₂ utilization; slow component; aging

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