title: Blood flow and muscle oxygenation during low, moderate, and maximal sustained isometric contractions.
abstract: A reduction of blood flow to active muscle will precipitate fatigue, and sustained isometric contractions produce intramuscular and compartmental pressures that can limit flow. The present study explored how blood flow and muscle oxygenation respond to isometric contractions at low, moderate, and maximal intensities. Over two visits, 10 males (26 ± 2 yr; means ± SD) performed 1-min dorsiflexion contractions at 30, 60, and 100% of maximal voluntary contraction (MVC) torque. Doppler ultrasound of the anterior tibial artery was used to record arterial diameter and mean blood velocity and to calculate absolute blood flow. The tissue oxygenation index (TOI) of tibialis anterior was acquired with near-infrared spectroscopy (NIRS). There was a progressive increase in blood flow at 30% MVC (peak of 289 ± 139% resting value), no change from rest until an increase in the final 10 s of exercise at 60% MVC (peak of 197 ± 102% rest), and an initial decrease (59 ± 30% resting value) followed by a progressive increase at 100% MVC (peak of 355 ± 133% rest). Blood flow was greater at 30 and 100% than 60% MVC during the last 30 s of exercise. TOI was ∼63% at rest and, within 30 s of exercise, reached steady-state values of ∼42%, ∼22%, and ∼22% for 30, 60, and 100% MVC, respectively. Even maximal contraction of the dorsiflexors is unable to cause more than a transient decrease of flow in the anterior tibial artery. Unlike dynamic or intermittent isometric exercise, our results indicate blood flow is not linearly graded with intensity or directly coupled with oxygenation during sustained isometric contractions.
authors.affiliation: Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada;
authors.forename: Chris J
authors.initials: CJ
authors.lastname: McNeil
authors.affiliation: School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, Ontario, Canada;
authors.forename: Matti D
authors.initials: MD
authors.lastname: Allen
authors.affiliation: School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, Ontario, Canada;
authors.forename: Eric
authors.initials: E
authors.lastname: Olympico
authors.affiliation: School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, Ontario, Canada; Department of Physiology and Pharmacology, The University of Western Ontario, London, Ontario, Canada; and.
authors.forename: J Kevin
authors.initials: JK
authors.lastname: Shoemaker
authors.affiliation: School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, Ontario, Canada; Department of Anatomy and Cell Biology, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, Ontario, Canada crice@uwo.ca.
authors.forename: Charles L
authors.identifier: http://orcid.org/0000-0002-0755-3164
authors.initials: CL
authors.lastname: Rice
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D001783:Blood Flow Velocity; D004576:Electromyography; D015444:Exercise; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D018763:Muscle Fatigue; D018482:Muscle, Skeletal / Q000098:blood supply* / Q000378:metabolism*; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption; D012039:Regional Blood Flow; D019265:Spectroscopy, Near-Infrared; D016909:Tibial Arteries / Q000000981:diagnostic imaging / Q000502:physiology*; D013997:Time Factors; D019415:Torque; D018608:Ultrasonography, Doppler; D055815:Young Adult
chemical_list: D010100:Oxygen
keywords: dorsiflexors; muscle blood flow; near-infrared spectroscopy