title: Skeletal muscle oxygenation during constant work rate exercise.
abstract: We compared the slow rise in VO2 during heavy exercise (i.e., greater than lactic acidosis threshold (LAT)) with changes in muscle oxyhemoglobin+oxymyoglobin (O2Hb/O2Mb) saturation by reflectance near infrared spectroscopy. Ten subjects performed four 6-min cycle ergometer tests with two constant work rates less than and two greater than the LAT, equivalent to 20, 40, 65 and 75% peak VO2. During less than LAT exercise, O2Hb/O2Mb saturation decreased to a minimum by 2 min and then remained constant or rose slightly. For greater than LAT work rates, the initial fall in O2Hb/O2Mb saturation was greater the higher the work rate and continued to decrease with time after 3 min. Between minutes 3 and 6, the rate of decrease in O2Hb/O2Mb saturation correlated with the increase in VO2 (r = -0.69, P < 0.0001). These studies support the hypothesis that the slow rise in VO2 during heavy constant work rate exercise is associated with a progressive decline in O2Hb/O2Mb saturation in the contracting muscles themselves that may be facilitated by capillary oxyhemoglobin dissociation owing to tissue lactic acidosis (Bohr effect).
authors.affiliation: Department of Medicine, Harbor-UCLA Medical Center, Torrance 90509, USA.
authors.forename: R
authors.initials: R
authors.lastname: Belardinelli
authors.forename: T J
authors.initials: TJ
authors.lastname: Barstow
authors.forename: J
authors.initials: J
authors.lastname: Porszasz
authors.forename: K
authors.initials: K
authors.lastname: Wasserman
mesh_terms: D000328:Adult; D015444:Exercise / Q000502:physiology*; D005260:Female; D006339:Heart Rate; D006801:Humans; D007773:Lactates / Q000097:blood; D019344:Lactic Acid; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology*; D011659:Pulmonary Gas Exchange; D013057:Spectrum Analysis
chemical_list: D007773:Lactates; D019344:Lactic Acid