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Am J Physiol Regul Integr Comp Physiol 294: R577-R584, 2008. First published November 21, 2007; doi:10.1152/ajpregu.00537.2007
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ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY

O2 uptake kinetics, pyruvate dehydrogenase activity, and muscle deoxygenation in young and older adults during the transition to moderate-intensity exercise

B. J. Gurd,1,2 S. J. Peters,6 G. J. F. Heigenhauser,5 P. J. LeBlanc,6 T. J. Doherty,4 D. H. Paterson,1,2 and J. M. Kowalchuk1,2,3

1Canadian Center for Activity and Aging, 2Faculty of Health Sciences, School of Kinesiology, 3Department of Physiology and Pharmacology, 4Faculty of Medicine and Dentistry, Departments of Clinical Neurological Sciences and Rehabilitation Medicine, The University of Western Ontario, London, Ontario; 5Department of Medicine, McMaster University, Hamilton, Ontario; and 6Faculty of Applied Health Sciences, Brock University, St. Catharines, Ontario, Canada

Submitted 26 July 2007 ; accepted in final form 14 November 2007

The adaptation of pulmonary O2 uptake (VO2p) kinetics is slowed in older compared with young adults during the transition to moderate-intensity exercise. In this study, we examined the relationship between VO2p 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 ~90% of estimated lactate threshold. Phase 2 VO2p 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 VO2p in older adults, and there was a similar time course of HHb accompanying the slower VO2p kinetics in the older adults, suggesting a slower adaptation of bulk O2 delivery in older adults. In conclusion, the slower adaptation of VO2p in older adults is likely a result of both an increased metabolic inertia and lower O2 availability.

work rate; lactate threshold


Address for reprint requests and other correspondence: J. M. Kowalchuk, Canadian Centre for Activity and Aging, School of Kinesiology, Faculty of Health Sciences, HSB 411C, The Univ. of Western Ontario, London, Ontario, Canada N6A 5B9 (e-mail: jkowalch{at}uwo.ca)






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