The present study examined whether an increased leg blood flow and oxygen (O2) delivery at onset of intense exercise would speed the rate of rise in leg oxygen uptake (VO2). Nine healthy males (25±1 years, mean±SEM : performed one-leg knee-extensor exercise (62±3 W, 86±3% of incremental test peak power) for 4 min during a control setting (CON) and with infusion of ATP into the femoral artery in order to increase blood flow before and during exercise. In ATP, femoral arterial blood flow (FABF) and O2 delivery were higher (P<0.001) at onset of exercise and throughout exercise (FABF after 10 s: 5.1±0.5 vs. 2.7±0.3 l min(-1); 45 s: 6.0±0.5 vs. 4.1±0.4 l min(-1), 90 s: 6.6±0.6 vs. 4.5±0.4 l min(-1) and 240 s: 7.0±0.6 vs. 5.1±0.3 l min(-1) in ATP and CON, respectively). Leg VO2 was not different in ATP and CON during the first 20 s of exercise but was lower (P<0.05) in ATP compared with CON after 30 s and until end of exercise (30 s: 436±42 vs. 549±45 ml min(-1) and 240 s: 705±31 vs. 814±59 ml min(-1) in ATP and CON, respectively). Lactate release was lower after 60, 120, and 180 s of exercise with ATP infusion. These results suggest that O2 delivery is not limiting the rise in skeletal muscle VO2 in the initial phase of intense exercise. This article is protected by copyright. All rights reserved.
Experimental Physiology, 2014, Vol 99, Issue 10, p. 1399-1408