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

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 Submitted 14 June 2004 ; accepted in final form 5 January 2005 The purpose was to examine the adaptation of pulmonary O 2 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 O 2 utilization; slow component; aging 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 )