The present study examined if a marked reduction in oxygen delivery, unlike findings with moderate intensity exercise, would slow leg oxygen uptake (VO2) kinetics during intense exercise (86±3% of incremental test peak power). Seven healthy males (26±1 years, mean±SEM) performed one-legged knee-extensor exercise (60±3 W) for 4 min in a control setting (CON) and with arterial infusion of L-NMMA and indomethacin in the working leg to reduce blood flow by inhibiting formation of nitric oxide and prostanoids (double blockade; DB). In DB leg blood flow (LBF) and oxygen delivery during the first minute of exercise were 25-50% lower (P<0.01) compared to CON (LBF after 10 s: 1.1±0.2 vs. 2.5±0.3 l min-1 and 45 s: 2.7±0.2 vs. 3.8±0.4 l min-1) and 15% lower (P<0.05) after 2 minutes of exercise. Leg VO2 in DB was attenuated (P<0.05) during the first two minutes of exercise (10 s: 161±26 vs. 288±34 ml min-1 and 45 s: 459±48 vs. 566±81 ml min-1) despite a higher (P<0.01) oxygen extraction in DB. Net leg lactate release was the same in DB and CON. The present study shows that a marked reduction in oxygen delivery can limit the rise in VO2 during the initial part of intense exercise. This is in contrast to previous observations during moderate intensity exercise using the same DB procedure which suggests that fast twitch muscle fibres are more sensitive to a reduction in oxygen delivery than slow twitch fibres.
- O2 extraction
- Blood flow regulation
- Fast twitch fibres
- VO2 kinetics
- Copyright © 2013, American Journal of Physiology - Regulatory, Integrative and Comparative Physiology