title: Low blood flow at onset of moderate-intensity exercise does not limit muscle oxygen uptake.
abstract: The effect of low blood flow at onset of moderate-intensity exercise on the rate of rise in muscle oxygen uptake was examined. Seven male subjects performed a 3.5-min one-legged knee-extensor exercise bout (24 +/- 1 W, mean +/- SD) without (Con) and with (double blockade; DB) arterial infusion of inhibitors of nitric oxide synthase (N(G)-monomethyl-l-arginine) and cyclooxygenase (indomethacin) to inhibit the synthesis of nitric oxide and prostanoids, respectively. Leg blood flow and leg oxygen delivery throughout exercise was 25-50% lower (P < 0.05) in DB compared with Con. Leg oxygen extraction (arteriovenous O(2) difference) was higher (P < 0.05) in DB than in Con (5 s: 127 +/- 3 vs. 56 +/- 4 ml/l), and leg oxygen uptake was not different between Con and DB during exercise. The difference between leg oxygen delivery and leg oxygen uptake was smaller (P < 0.05) during exercise in DB than in Con (5 s: 59 +/- 12 vs. 262 +/- 39 ml/min). The present data demonstrate that muscle blood flow and oxygen delivery can be markedly reduced without affecting muscle oxygen uptake in the initial phase of moderate-intensity exercise, suggesting that blood flow does not limit muscle oxygen uptake at the onset of exercise. Additionally, prostanoids and/or nitric oxide appear to play important roles in elevating skeletal muscle blood flow in the initial phase of exercise.
authors.affiliation: The Copenhagen Muscle Research Centre, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Michael
authors.initials: M
authors.lastname: Nyberg
authors.forename: Stefan P
authors.initials: SP
authors.lastname: Mortensen
authors.forename: Bengt
authors.initials: B
authors.lastname: Saltin
authors.forename: Ylva
authors.initials: Y
authors.lastname: Hellsten
authors.forename: Jens
authors.initials: J
authors.lastname: Bangsbo
mesh_terms: D000328:Adult; D000077463:Carbamide Peroxide; D016861:Cyclooxygenase Inhibitors / Q000008:administration & dosage; D004338:Drug Combinations; D004791:Enzyme Inhibitors / Q000008:administration & dosage; D015444:Exercise / Q000502:physiology*; D005263:Femoral Artery / Q000502:physiology; D006801:Humans; D007213:Indomethacin / Q000008:administration & dosage*; D007866:Leg / Q000098:blood supply; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D009569:Nitric Oxide / Q000378:metabolism; D019335:Nitroarginine / Q000008:administration & dosage*; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology*; D010545:Peroxides / Q000097:blood; D011453:Prostaglandins / Q000378:metabolism; D012039:Regional Blood Flow / Q000187:drug effects / Q000502:physiology*; D014508:Urea / Q000031:analogs & derivatives / Q000097:blood; D055815:Young Adult
chemical_list: D016861:Cyclooxygenase Inhibitors; D004338:Drug Combinations; D004791:Enzyme Inhibitors; D010545:Peroxides; D011453:Prostaglandins; D019335:Nitroarginine; D009569:Nitric Oxide; D000077463:Carbamide Peroxide; D014508:Urea; D007213:Indomethacin