title: O2 uptake kinetics, pyruvate dehydrogenase activity, and muscle deoxygenation in young and older adults during the transition to moderate-intensity exercise.
abstract: The adaptation of pulmonary O(2) uptake (Vo(2)(p)) kinetics is slowed in older compared with young adults during the transition to moderate-intensity exercise. In this study, we examined the relationship between Vo(2)(p) kinetics and mitochondrial pyruvate dehydrogenase (PDH) activity in young (n = 7) and older (n = 6) adults. Subjects performed cycle exercise to a work rate corresponding to approximately 90% of estimated lactate threshold. Phase 2 Vo(2)(p) kinetics were slower (P < 0.05) in older (tau = 40 +/- 17 s) compared with young (tau = 21 +/- 6 s) adults. Relative phosphocreatine (PCr) breakdown was greater (P < 0.05) at 30 s in older compared with young adults. Absolute PCr breakdown at 6 min was greater (P < 0.05) in older compared with young adults. In young adults, PDH activity increased (P < 0.05) from baseline to 30 s, with no further change observed at 6 min. In older adults, PDH activity during baseline exercise was similar to that seen in young adults. During the exercise transition, PDH activity did not increase (P > 0.05) at 30 s of exercise but was elevated (P < 0.05) after 6 min. The change in deoxyhemoglobin (HHb) was greater for a given Vo(2)(p) in older adults, and there was a similar time course of HHb accompanying the slower Vo(2)(p) kinetics in the older adults, suggesting a slower adaptation of bulk O(2) delivery in older adults. In conclusion, the slower adaptation of Vo(2)(p) in older adults is likely a result of both an increased metabolic inertia and lower O(2) availability.
authors.affiliation: Canadian Centre for Activity and Aging, School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, Ontario, Canada.
authors.forename: B J
authors.initials: BJ
authors.lastname: Gurd
authors.forename: S J
authors.initials: SJ
authors.lastname: Peters
authors.forename: G J F
authors.initials: GJ
authors.lastname: Heigenhauser
authors.forename: P J
authors.initials: PJ
authors.lastname: LeBlanc
authors.forename: T J
authors.initials: TJ
authors.lastname: Doherty
authors.forename: D H
authors.initials: DH
authors.lastname: Paterson
authors.forename: J M
authors.initials: JM
authors.lastname: Kowalchuk
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000378:metabolism*; D004789:Enzyme Activation / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D019344:Lactic Acid / Q000378:metabolism; D008928:Mitochondria / Q000201:enzymology; D018482:Muscle, Skeletal / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D010766:Phosphorylation; D011768:Pyruvate Dehydrogenase Complex / Q000378:metabolism*; D019265:Spectroscopy, Near-Infrared
chemical_list: D006454:Hemoglobins; D011768:Pyruvate Dehydrogenase Complex; D019344:Lactic Acid; C100003:deoxyhemoglobin