Non-invasive quantitative assessment of oxidative metabolism in quadricepsmuscles by near infrared spectroscopy

Background-Near infrared spectroscopy can be used in non-invasive monitorin g of changes in skeletal muscle oxygenation in exercising subjects. Objective-To evaluate whether this method can be used to assess metabolic c apacity of muscles. Two distinctive variables abstracted from a curve of ch anges in muscle oxygenation were assessed. Methods-Exercise on a cycle ergometer was performed by 18 elite male athlet es and eight healthy young men. A measuring probe was placed on the skin of the quadriceps muscle to measure reflected light at two wavelengths (760 a nd 850 nm), so that the relative index of muscle oxygenation could be calcu lated. Exercise intensity was increased from 50 W in 50 W increments until the subject was exhausted. During exercise, changes in muscle oxygenation a nd blood lactate concentration were recorded. The following two variables f or assessment of muscle oxygenation were then abstracted and analysed by pl otting curves of changes in muscle oxygenation: the rate of recovery of mus cle oxygen saturation (R-R) and the relative value of the effective decreas e in muscle oxygenation (D-eff). Results-Data analysis showed a correlation between muscle oxygenation and b lood lactate concentration at the various exercise intensities and verified the feasibility of the experiment. Data for the athletes were compared wit h those for the controls using the Aspin-Welch test of significance; t = 2. 3 and 2.86 for R-R and D-eff respectively. There were significant differenc es (p = 0.05) between the athletes and the control group with respect to th ese two variables. Conclusion-R-R and D-eff may be distinctive variables that can be used to c haracterise muscle oxidative metabolism during human body movement.