Submitted on July 26, 2007
Accepted on November 14, 2007
O2 uptake kinetics and pyruvate dehydrogenase activity and muscle deoxygenation in young and older adults during the transition to moderate-intensity exercise
Brendon J. Gurd1, Sandra J. Peters2, George JF Heigenhauser3, Paul J. LeBlanc4, Timothy J Doherty5, Donald H. Paterson6, and John M. Kowalchuk7*
1 School of Kinesiology, The University of Western Ontario, London, Canada
2 Phys Ed and Kinesiology, Brock University, St. Catharines, Canada
3 Department of Medicine, McMaster University, Hamilton, Canada
4 Community Health Sciences, Brock University, St. Catharines, Canada
5 Depts. of Clinical Neuro Sciences & Rehab Med, The University of Western Ontario, London, Canada
6 School of Kinesiology, University of Western Ontario, London, Canada
7 School of Kinesiology, The University Western Ontario, London, Canada
* To whom correspondence should be addressed. E-mail: jkowalch{at}uwo.ca.
The adaptation of pulmonary oxygen uptake (VO2p) kinetics are slowed in older compared to young adults during the transition to moderate-intensity exercise. In this study we examined the relationship between VO2p kinetics and mitochondrial pyruvate dehydrogenase (PDH) in young (n = 7) and older (n = 6) adults. Subjects performed cycle exercise to a work rate (WR) corresponding to ~90% of estimated lactate threshold. Phase 2 VO2p kinetics were slower (P < 0.05) in older (
= 40 ± 17 s) compared to young ( = 21 ± 6). Relative phosphocreatine (PCr) breakdown was greater (P < 0.05) at 30 s in older compared to young. Absolute PCr breakdown at 6 min was greater (P < 0.05) in older compared to young. 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 exercise but was elevated (P < 0.05) after 6 min). 
HHb was greater for a given VO2 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.
