In vivo quantitative near-infrared spectroscopy in skeletal muscle and bone during rest and isometric exercise

In this study quantitative near-infrared-spectroscopy (NIRS) was investigated as a potential tool to measure local O2 consumption (mVO2) in human bone (tibia) in comparison with muscle (musculus tibialis anterior). Both tissues were examined at rest and during 80% maximum voluntary isometric muscle contraction. Fifteen subjects were tested. Local variations in oxy-hemoglobin (O2Hb), desoxy-hemoglobin (HHb), and total hemoglobin (tHb) were investigated with a continuously operating NIRS system. mVO2 was determined in phases of applied arterial occlusion. At rest mVO2 was five times higher in muscle than in bone. However, both mVO2 values showed a distinct correlation with skin-fold thickness. At rest and only in bone we recorded a periodical variation of O2Hb. HHb was almost constant. This variation of O2Hb and the resulting variation in tHb indicated chances in blood volume, which are not compatible with the solid nature of bone. During muscle contraction, mVO2 in muscle increased about twenty fold. As expected, mVO2 in bone did not significantly increase during muscle contraction. In conclusion, NIRS was confirmed as a valid method to determine the excess mVO2 in muscle during contraction. For mVO2 measurements in bone more sophisticated localization techniques are required to separate the effects derived from bone and skin.