Skeletal muscle oxygenation during constant work rate exercise

Med Sci Sports Exerc. 1995 Apr;27(4):512-9.


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).

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adult
  • Exercise / physiology*
  • Female
  • Heart Rate
  • Humans
  • Lactates / blood
  • Lactic Acid
  • Male
  • Muscle, Skeletal / physiology*
  • Oxygen Consumption / physiology*
  • Pulmonary Gas Exchange
  • Spectrum Analysis


  • Lactates
  • Lactic Acid