The isometric torque at which knee-extensor muscle reoxygenation stops

• Published in: Medicine and science in sports and exercise Vol. 39; no. 3; p. 443
• Main Authors: de Ruiter, C J, Goudsmit, Jos F A, Van Tricht, Johannes A, de Haan, Arnold
• Format: Journal Article
• Language: English
• Published: United States 01.03.2007
• Subjects: Adult; Exercise - physiology; Fatigue - physiopathology; Humans; Isometric Contraction - physiology; Knee - physiology; Male; Muscle, Skeletal - blood supply; Muscle, Skeletal - physiology; Pilot Projects; Prospective Studies; Torque
• ISSN: 0195-9131
• DOI: 10.1249/mss.0b013e31802dd3cc

We investigated the knee-extensor torque at which reoxygenation (inflow of arterial blood) during an isometric contraction stopped, whether this torque depended on maximal torque capacity (MTC), and whether there were differences among the synergists. Isometric knee-extension torque was measured using a dynamometer with 90 degrees angles in the hip and knee. Maximal voluntary activation (established with superimposed nerve stimulation) was > 90% in the 15 healthy male subjects (20-30 yr). Near-infrared spectroscopy (NIRS) was used to measure changes in muscle oxygenation of the vastus medialis (VM), vastus lateralis (VL), and rectus femoris (RF) muscle during submaximal isometric contractions at intensities of 20-45% MTC with 5% increments, applied in randomized order and divided over 2 d. At each torque, a contraction with an inflated pressure cuff (450 mm Hg), inducing full arterial occlusion, was followed (10 min of rest) by a second contraction without the cuff. MTC ranged from 178 to 348 N.m. The torque at which maximal deoxygenation (all oxygen consumed) during contraction without the cuff became similar (P < 0.05) to the maximal deoxygenation reached with the cuff (indicative for complete occlusion of blood flow during the contraction without the cuff) was significantly higher for the RF (35% MTC) than for both vasti (25% MTC). There was no significant relation between MTC and relative (% MTC) torque at which muscle reoxygenation stopped. Knee-extensor reoxygenation stopped at lower torques than previously reported for blood flow in this muscle, and this occurred at the same % MTC in subjects of different strength but at different % MTC for the different synergists.