title: The isometric torque at which knee-extensor muscle reoxygenation stops.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Institute for Fundamental and Clinical Human Movement Sciences, Vrije University, Amsterdam, The Netherlands. C_J_de_Ruiter@FBW.VU.NL
authors.forename: C J
authors.initials: CJ
authors.lastname: de Ruiter
authors.forename: Jos F A
authors.initials: JF
authors.lastname: Goudsmit
authors.forename: Johannes A
authors.initials: JA
authors.lastname: Van Tricht
authors.forename: Arnold
authors.initials: A
authors.lastname: de Haan
mesh_terms: D000328:Adult; D015444:Exercise / Q000502:physiology*; D005221:Fatigue / Q000503:physiopathology; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D007717:Knee / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000098:blood supply / Q000502:physiology*; D010865:Pilot Projects; D011446:Prospective Studies; D019415:Torque