DETERMINATION OF OXYGEN-CONSUMPTION IN MUSCLE DURING EXERCISE USING NEAR-INFRARED SPECTROSCOPY

The aim of this study was to determine oxygen consumption (VO2) during isometric exercise in human muscles using near infrared spectroscopy (MRS). The technique was used to study the relationship between VO2 in the soleus muscle and the level of isometric exercise expressed as pe rcentages of the maximum voluntary contraction (MVC). For the study 11 healthy male volunteers were recruited. Reproducibility was studied i n 6 subjects. The subjects were seated in a chair with the knee joint at an angle of 90 degrees. The optodes of the NIRS instrument were att ached to the lateral aspect of the soleus muscle. A horizontal bar abo ve the knee was connected to a dynamometer. Subjects applied isometric force to the bar by producing a torque at the ankle joint. Firstly th e MVC was determined. Secondly the VO2 at rest and at 5 levels of isom etric exercise, ranging from 5% to 25% of MVC and increasing by 5% eac h stage, was measured. In all cases the VO2 at rest or during isometri c contraction was determined from the decrease of the oxyhaemoglobin ( O(2)Hb) signal immediately after arterial occlusion of the thigh. Repe ated measurements showed no significant difference between trials, ind icating that the measurements were reproducible. At rest a VO2 of 6.7 +/- 1.1 mu MO(2)Hb . min(-1) (mean +/- S.E.M.) was found, a result com parable with other studies. In all subjects a linear relationship was found between the VO2 and the level of exercise. The average slope of the regression lines of all individuals was 0.85 +/- 0.22 mu MO(2)Hb . min(-1).%MVC(-1) (mean +/- S.E.M.). Inter-individual variation of the slopes was high and ranged from 0.28 to 2.29 mu MO(2)Hb . min(-1)%MVC (-1), which can be explained by differences in fat percentage and in t he measuring volume of the NIRS instrument. NIRS appeared to be a repr oducible and reliable method for the non-invasive measurement of VO2 i n human muscles. The method could be used to investigate regional diff erences as well as changes in time between muscle groups as a function of training.