title: The near-infrared spectroscopy-derived deoxygenated haemoglobin breaking-point is a repeatable measure that demarcates exercise intensity domains.
abstract: OBJECTIVE
  A breaking-point in the near-infrared spectroscopy (NIRS)-derived deoxygenated haemoglobin ([HHb]) profile towards the end of a ramp incremental (RI) cycling test has been associated to the respiratory compensation point (RCP). Despite the physiological value of this measure, its repeatability remains unknown. The aim was to examine the repeatability of the [HHb] breaking-point ([HHb]BP) and its association to RCP during a RI cycling test.
  
  
  METHODS
  A repeated measures design was performed on 11 males (30.5±8.4 year; 76.5±8.4kg) and 4 females (30.5±5.9 year; 61.9±4.4 Kg).
  
  
  METHODS
  Gas exchange and NIRS [HHb] data were collected during RI tests performed on two different days separated by 48h. The [HHb]BP and the RCP were determined and compared for each trial.
  
  
  RESULTS
  The [HHb]BP and the respiratory compensation point (RCP) occurred at the same VO2in test 1 and test 2 ([HHb]BP: 3.49±0.52Lmin-1test 1; 3.48±0.45Lmin-1test 2; RCP: 3.38±0.40Lmin-1test 1; 3.38±0.44Lmin-1test 2) (P>0.05). The VO2associated with the [HHb]BP and the VO2at RCP were not significantly different from each other either in test 1 as well as in test 2 (P>0.05). Neither test 1 nor test 2 showed significant mean average error between the VO2at the [HHb]BP and RCP using Bland & Altman plots.
  
  
  CONCLUSIONS
  The [HHb]BP is a repeatable measure that consistently occurs towards the end of a RI test. The association between the [HHb]BP and the RCP reinforces the idea that these parameters may share similar mechanistic basis.
authors.affiliation: Faculty of Kinesiology, University of Calgary, Canada.
authors.forename: Danilo
authors.initials: D
authors.lastname: Iannetta
authors.affiliation: Faculty of Kinesiology, University of Calgary, Canada.
authors.forename: Ahmad
authors.initials: A
authors.lastname: Qahtani
authors.affiliation: Faculty of Kinesiology, University of Calgary, Canada.
authors.forename: Felipe
authors.initials: F
authors.lastname: Mattioni Maturana
authors.affiliation: Faculty of Kinesiology, University of Calgary, Canada. Electronic address: jmmurias@ucalgary.ca.
authors.forename: Juan Manuel
authors.initials: JM
authors.lastname: Murias
mesh_terms: D000328:Adult; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005260:Female; D006454:Hemoglobins / Q000032:analysis*; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology; D010101:Oxygen Consumption; D011659:Pulmonary Gas Exchange; D015203:Reproducibility of Results; D019265:Spectroscopy, Near-Infrared; D055815:Young Adult
chemical_list: D006454:Hemoglobins; C100003:deoxyhemoglobin
keywords: Near-infrared spectroscopy; Ramp incremental test; Respiratory compensation point