title: Effect of blood flow restriction on tissue oxygenation during knee extension.
abstract: OBJECTIVE
  Time-resolved near-infrared spectroscopy was used to quantify tissue oxy- and deoxyhemoglobin concentrations ([HbO2] and [HbR]) and O2 saturation (stO2) in the oblique fibers of the vastus medialis muscle and brain prefrontal cortex during knee extension with and without blood flow restriction (BFR).
  
  
  METHODS
  Six young healthy males performed three sets of knee extensions on a dynamometer (50% one-repetition maximum) separated by 90-s rest periods in three conditions: 1) until fatigue without BFR (fatigue), 2) until fatigue with BFR (100 mm Hg cuff constriction around thigh (BFR)), 3) same number of repetitions from condition 2 without BFR (matched). Each condition was performed on a separate visit.
  
  
  RESULTS
  BFR was associated with higher [HbR] at the oblique fibers of the vastus medialis muscle (rest 1: 57.8 (BFR) vs 35.0 μM (matched); P < 0.0001) and a significantly lower stO2 during recovery periods between sets (7.5%-11.2 % lower than non-BFR conditions for rest 1 and 2, P < 0.0001). Using a piecewise linear spline method, a spike in [HbR] was observed before the onset of HbR clearance during recovery, causing HbR clearance to begin at a higher concentration (81 (BFR) vs 62 μM (matched), P = 0.029). [HbO2] kinetics during recovery were also affected by BFR, with longer duration (BFR, 51 s; matched, 31 s; P = 0.047) but lower rate of increase (BFR, 58 μM·min; matched, 89 μM·min; P = 0.004) during recovery. In the prefrontal cortex, BFR was associated with increased [HbR], diminished increase in [HbO2], and higher subjective exertion.
  
  
  CONCLUSIONS
  These findings yield insight into possible physiological mechanisms of BFR and suggest a role of time-resolved near-infrared spectroscopy in monitoring and optimization of BFR exercise on an individual basis.
authors.affiliation: 1Beckman Laser Institute and Medical Clinic, School of Medicine, University of California, Irvine, CA; 2Department of Pediatrics, Irvine School of Medicine, University of California, Irvine, CA; 3Department of Orthopedic Surgery, University of California, Irvine, CA; and 4Department of Kinesiology, California State University, Long Beach, CA.
authors.forename: Goutham
authors.initials: G
authors.lastname: Ganesan
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Cotter
authors.forename: Warren
authors.initials: W
authors.lastname: Reuland
authors.forename: Albert E
authors.initials: AE
authors.lastname: Cerussi
authors.forename: Bruce J
authors.initials: BJ
authors.lastname: Tromberg
authors.forename: Pietro
authors.initials: P
authors.lastname: Galassetti
mesh_terms: D005080:Exercise Test; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D007717:Knee / Q000502:physiology; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D010100:Oxygen / Q000378:metabolism; D010108:Oxyhemoglobins / Q000378:metabolism; D010807:Physical Endurance / Q000502:physiology*; D017397:Prefrontal Cortex / Q000378:metabolism; D052097:Quadriceps Muscle / Q000098:blood supply* / Q000378:metabolism / Q000502:physiology*; D020127:Recovery of Function; D012039:Regional Blood Flow / Q000502:physiology; D055070:Resistance Training / Q000379:methods; D019265:Spectroscopy, Near-Infrared
chemical_list: D006454:Hemoglobins; D010108:Oxyhemoglobins; C100003:deoxyhemoglobin; D010100:Oxygen