title: Leg oxygen uptake in the initial phase of intense exercise is slowed by a marked reduction in oxygen delivery.
abstract: The present study examined whether a marked reduction in oxygen delivery, unlike findings in 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, means ± SE) performed one-legged knee-extensor exercise (60 ± 3 W) for 4 min in a control setting (CON) and with arterial infusion of N(G)-monomethyl-l-arginine 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 with CON (LBF after 10 s: 1.1 ± 0.2 vs. 2.5 ± 0.3 l/min and 45 s: 2.7 ± 0.2 vs. 3.8 ± 0.4 l/min) and 15% lower (P < 0.05) after 2 min of exercise. Leg Vo2 in DB was attenuated (P < 0.05) during the first 2 min of exercise (10 s: 161 ± 26 vs. 288 ± 34 ml/min and 45 s: 459 ± 48 vs. 566 ± 81 ml/min) 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 fibers are more sensitive to a reduction in oxygen delivery than slow-twitch fibers.
authors.affiliation: Department of Nutrition, Exercise and Sports, Section of Integrated Physiology, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Christensen
authors.forename: Michael
authors.initials: M
authors.lastname: Nyberg
authors.forename: Stefan P
authors.initials: SP
authors.lastname: Mortensen
authors.forename: Jens Jung
authors.initials: JJ
authors.lastname: Nielsen
authors.forename: Niels H
authors.initials: NH
authors.lastname: Secher
authors.forename: Rasmus
authors.initials: R
authors.lastname: Damsgaard
authors.forename: Ylva
authors.initials: Y
authors.lastname: Hellsten
authors.forename: Jens
authors.initials: J
authors.lastname: Bangsbo
mesh_terms: D000328:Adult; D001784:Blood Gas Analysis; D001794:Blood Pressure / Q000502:physiology; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D003627:Data Interpretation, Statistical; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015444:Exercise / Q000502:physiology*; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007213:Indomethacin / Q000494:pharmacology; D019344:Lactic Acid / Q000097:blood; D007866:Leg / Q000098:blood supply / Q000502:physiology*; D008297:Male; D018656:Muscle Fibers, Fast-Twitch / Q000187:drug effects / Q000502:physiology; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000097:blood; D011999:Recruitment, Neurophysiological / Q000187:drug effects / Q000502:physiology; D012039:Regional Blood Flow / Q000502:physiology; D019323:omega-N-Methylarginine / Q000494:pharmacology
chemical_list: D016861:Cyclooxygenase Inhibitors; D004791:Enzyme Inhibitors; D019323:omega-N-Methylarginine; D019344:Lactic Acid; D011188:Potassium; D007213:Indomethacin
keywords: Vo2 kinetics; blood flow regulation; oxygen extraction