Simultaneous in vivo measurements of HbO2 saturation and PCr kinetics after exercise in normal humans

J Appl Physiol (1985). 1994 Jul;77(1):5-10. doi: 10.1152/jappl.1994.77.1.5.


Simultaneous measurements of phosphocreatine (PCr) and oxyhemoglobin (HbO2) saturation were made during recovery from exercise in calf muscles of five male subjects. PCr was measured using magnetic resonance spectroscopy in a 2.0-T 78-cm-bore magnet with a 9-cm-diam surface coil. Relative HbO2 saturation was measured as the difference in absorption of 750- and 850-nm light with use of near-infrared spectroscopy. The light source and detectors were 3 cm apart. Exercise consisted of isokinetic plantar flexion in a supine position. Two 5-min submaximal protocols were performed with PCr depletion to 60% of resting values and with pH values of > 7.0. Then two 1-min protocols of rapid plantar flexion were performed to deplete PCr values to 5-20% of resting values with pH values of < 6.8. Areas of PCr peaks (every 8 s) and HbO2 saturation (every 1 s) were fit to a monoexponential function, and a time constant was calculated. The PCr time constant was larger after maximal exercise (68.3 +/- 10.5 s) than after submaximal exercise (36.0 +/- 6.5 s), which is consistent with the effects of low pH on PCr recovery. HbO2 resaturation approximated submaximal PCr recovery and was not different between maximal (29.4 +/- 5.5 s) and submaximal (27.6 +/- 6.0 s) exercise. We conclude that magnetic resonance spectroscopy measurements of PCr recovery and near-infrared spectroscopy measurements of recovery of HbO2 saturation provide similar information as long as muscle pH remains near 7.0.

Publication types

  • Clinical Trial

MeSH terms

  • Adult
  • Exercise / physiology*
  • Hemoglobins / analysis
  • Hemoglobins / metabolism*
  • Humans
  • Hydrogen-Ion Concentration
  • Kinetics
  • Leg / physiology
  • Magnetic Resonance Spectroscopy
  • Male
  • Muscle, Skeletal / physiology
  • Oxygen / analysis
  • Oxygen Consumption / physiology*
  • Phosphocreatine / metabolism*
  • Spectrophotometry, Infrared


  • Hemoglobins
  • Phosphocreatine
  • Oxygen