Effects of prior heavy-intensity exercise on pulmonary O2 uptake and muscle deoxygenation kinetics in young and older adult humans

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 N6A 3K7 Submitted 1 December 2003 ; accepted in final form 27 April 2004 Pulmonary O 2 uptake ( O 2p ) and muscle deoxygenation kinetics were examined during moderate-intensity cycling (80% lactate threshold) without warm-up and after heavy-intensity warm-up exercise in young ( n = 6; 25 ± 3 yr) and older ( n = 5; 68 ± 3 yr) adults. We hypothesized that heavy warm-up would speed O 2p kinetics in older adults consequent to an improved intramuscular oxygenation. Subjects performed step transitions ( n = 4; 6 min) from 20 W to moderate-intensity exercise preceded by either no warm-up or heavy-intensity warm-up (6 min). O 2p was measured breath by breath. Oxy-, deoxy-(HHb), and total hemoglobin and myoglobin (Hb tot ) of the vastus lateralis muscle were measured continuously by near-infrared spectroscopy (NIRS). O 2p (phase 2; ) and HHb data were fit with a monoexponential model. After heavy-intensity warm-up, oxyhemoglobin (older subjects: 13 ± 9 µM; young subjects: 9 ± 8 µM) and Hb tot (older subjects: 12 ± 8 µM; young subjects: 14 ± 10 µM) were elevated ( P < 0.05) relative to the no warm-up pretransition baseline. In older adults, O 2p adapted at a faster rate ( P < 0.05) after heavy warm-up (30 ± 7 s) than no warm-up (38 ± 5 s), whereas in young subjects, O 2p was similar in no warm-up (26 ± 7 s) and heavy warm-up (25 ± 5 s). HHb adapted at a similar rate in older and young adults after no warm-up; however, in older adults after heavy warm-up, the adaptation of HHb was slower ( P < 0.01) compared with young and no warm-up. These data suggest that, in older adults, O 2p kinetics may be limited by a slow adaptation of muscle blood flow and O 2 delivery. near-infrared spectroscopy; muscle oxygen utilization; 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 ).