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

Pulmonary O-2 uptake ((V) over dot 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 (V) over dot 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). (V) over dot 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). (V) over dot O-2p ( phase 2; tau) and HHb data were fit with a monoexponential model. After heavy-intensity warm-up, oxyhemoglobin (older subjects: 13 +/- 9 muM; young subjects: 9 +/- 8 muM) and Hb(tot) (older subjects: 12 +/- 8 muM; young subjects: 14 +/- 10 muM) were elevated ( P < 0.05) relative to the no warm-up pretransition baseline. In older adults, tau(V) over dot 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, tau (V) over dot 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, (V) over dot O-2p kinetics may be limited by a slow adaptation of muscle blood flow and O-2 delivery.