title: Adaptation of pulmonary O2 uptake kinetics and muscle deoxygenation at the onset of heavy-intensity exercise in young and older adults.
abstract: The purpose was to examine the adaptation of pulmonary O(2) uptake (Vo(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. Vo(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). Vo(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 Vo(2p) [phase 2, time constant (tau) of Vo(2p)] and HHb [following the time delay (TD) from exercise onset to the start of an increase in HHb] data. The tauVo(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 tau HHb following TD was faster (P < 0.05) in O (8 +/- 2 s) than Y (14 +/- 2 s). The slower Vo(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 Vo(2p) in O. This suggests that the slowed Vo(2p) kinetics in O may be a consequence of a slower adaptation of local muscle blood flow relative to that in Y.
authors.affiliation: Canadian Centre for Activity and Aging, School of Kinesiology, The University of Western Ontario, London, Ontario, Canada N6A 3K7.
authors.forename: Darren S
authors.initials: DS
authors.lastname: DeLorey
authors.forename: John M
authors.initials: JM
authors.lastname: Kowalchuk
authors.forename: Donald H
authors.initials: DH
authors.lastname: Paterson
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D005080:Exercise Test / Q000379:methods; D006801:Humans; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology*; D012123:Pulmonary Ventilation / Q000502:physiology*