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

Pulmonary O₂ uptake (VO_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 VO_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). VO_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). VO_2p (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 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, τVO_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, τVO_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, VO_2p kinetics may be limited by a slow adaptation of muscle blood flow and O₂ delivery. [ABSTRACT FROM AUTHOR]