title: Oxygenation Threshold Derived from Near-Infrared Spectroscopy: Reliability and Its Relationship with the First Ventilatory Threshold.
abstract: BACKGROUND
  Near-infrared spectroscopy (NIRS) measurements of oxygenation reflect O2 delivery and utilization in exercising muscle and may improve detection of a critical exercise threshold.
  
  
  OBJECTIVE
  First, to detect an oxygenation breakpoint (Δ[O2HbMb-HHbMb]-BP) and compare this breakpoint to ventilatory thresholds during a maximal incremental test across sexes and training status. Second, to assess reproducibility of NIRS signals and exercise thresholds and investigate confounding effects of adipose tissue thickness on NIRS measurements.
  
  
  METHODS
  Forty subjects (10 trained male cyclists, 10 trained female cyclists, 11 endurance trained males and 9 recreationally trained males) performed maximal incremental cycling exercise to determine Δ[O2HbMb-HHbMb]-BP and ventilatory thresholds (VT1 and VT2). Muscle haemoglobin and myoglobin O2 oxygenation ([HHbMb], [O2HbMb], SmO2) was determined in m. vastus lateralis. Δ[O2HbMb-HHbMb]-BP was determined by double linear regression. Trained cyclists performed the maximal incremental test twice to assess reproducibility. Adipose tissue thickness (ATT) was determined by skinfold measurements.
  
  
  RESULTS
  Δ[O2HbMb-HHbMb]-BP was not different from VT1, but only moderately related (r = 0.58-0.63, p<0.001). VT1 was different across sexes and training status, whereas Δ[O2HbMb-HHbMb]-BP differed only across sexes. Reproducibility was high for SmO2 (ICC = 0.69-0.97), Δ[O2HbMb-HHbMb]-BP (ICC = 0.80-0.88) and ventilatory thresholds (ICC = 0.96-0.99). SmO2 at peak exercise and at occlusion were strongly related to adipose tissue thickness (r2 = 0.81, p<0.001; r2 = 0.79, p<0.001). Moreover, ATT was related to asymmetric changes in Δ[HHbMb] and Δ[O2HbMb] during incremental exercise (r = -0.64, p<0.001) and during occlusion (r = -0.50, p<0.05).
  
  
  CONCLUSIONS
  Although the oxygenation threshold is reproducible and potentially a suitable exercise threshold, VT1 discriminates better across sexes and training status during maximal stepwise incremental exercise. Continuous-wave NIRS measurements are reproducible, but strongly affected by adipose tissue thickness.
authors.affiliation: Department of Human Movement Sciences, Vrije Universiteit Amsterdam, MOVE Research Institute Amsterdam, the Netherlands.
authors.forename: Stephan
authors.identifier: http://orcid.org/0000-0002-8296-828X
authors.initials: S
authors.lastname: van der Zwaard
authors.affiliation: Department of Human Movement Sciences, Vrije Universiteit Amsterdam, MOVE Research Institute Amsterdam, the Netherlands.
authors.forename: Richard T
authors.initials: RT
authors.lastname: Jaspers
authors.affiliation: Department of Human Movement Sciences, Vrije Universiteit Amsterdam, MOVE Research Institute Amsterdam, the Netherlands.
authors.forename: Ilse J
authors.initials: IJ
authors.lastname: Blokland
authors.affiliation: Department of Human Movement Sciences, Vrije Universiteit Amsterdam, MOVE Research Institute Amsterdam, the Netherlands.
authors.forename: Chantal
authors.initials: C
authors.lastname: Achterberg
authors.affiliation: Department of Human Movement Sciences, Vrije Universiteit Amsterdam, MOVE Research Institute Amsterdam, the Netherlands.
authors.forename: Jurrian M
authors.initials: JM
authors.lastname: Visser
authors.affiliation: Department of Human Movement Sciences, Vrije Universiteit Amsterdam, MOVE Research Institute Amsterdam, the Netherlands.
authors.forename: Anne R
authors.initials: AR
authors.lastname: den Uil
authors.affiliation: Department of Human Movement Sciences, Vrije Universiteit Amsterdam, MOVE Research Institute Amsterdam, the Netherlands.|Faculty of Sports and Nutrition, Amsterdam University of Applied Sciences, Amsterdam, the Netherlands.
authors.forename: Mathijs J
authors.initials: MJ
authors.lastname: Hofmijster
authors.affiliation: Department of Human Movement Sciences, Vrije Universiteit Amsterdam, MOVE Research Institute Amsterdam, the Netherlands.
authors.forename: Koen
authors.initials: K
authors.lastname: Levels
authors.affiliation: Department of Human Movement Sciences, Vrije Universiteit Amsterdam, MOVE Research Institute Amsterdam, the Netherlands.
authors.forename: Dionne A
authors.initials: DA
authors.lastname: Noordhof
authors.affiliation: Department of Human Movement Sciences, Vrije Universiteit Amsterdam, MOVE Research Institute Amsterdam, the Netherlands.
authors.forename: Arnold
authors.initials: A
authors.lastname: de Haan
authors.affiliation: Department of Human Movement Sciences, Vrije Universiteit Amsterdam, MOVE Research Institute Amsterdam, the Netherlands.
authors.forename: Jos J
authors.initials: JJ
authors.lastname: de Koning
authors.affiliation: Department of Physiology, VU Medical Center, Amsterdam, the Netherlands.
authors.forename: Willem J
authors.initials: WJ
authors.lastname: van der Laarse
authors.affiliation: Department of Human Movement Sciences, Vrije Universiteit Amsterdam, MOVE Research Institute Amsterdam, the Netherlands.
authors.forename: Cornelis J
authors.initials: CJ
authors.lastname: de Ruiter
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism; D005260:Female; D006801:Humans; D008297:Male; D010100:Oxygen / Q000378:metabolism*; D015203:Reproducibility of Results; D019265:Spectroscopy, Near-Infrared / Q000379:methods*
chemical_list: D010100:Oxygen