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

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Abstract
Pulmonary O2 uptake (V̇o2p) 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 V̇o2p 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). V̇o2p was measured breath by breath. Oxy-, deoxy-(HHb), and total hemoglobin and myoglobin (Hbtot) of the vastus lateralis muscle were measured continuously by near-infrared spectroscopy (NIRS). V̇o2p (phase 2; τ) 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 Hbtot (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, τV̇o2p 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, τV̇o2p 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, V̇o2p kinetics may be limited by a slow adaptation of muscle blood flow and O2 delivery.