Imaging of Regional Differences of Muscle Oxygenation during Exercise Using Spatially Resolved NIRS

The development of imaging systems using near-infrared spectroscopy (NIRS) has enabled noninvasive measurement of regional changes in muscle oxygenation. A spatially resolved NIRS (SR-NIRS) imaging instrument was utilized for real-time measurement of spatial-temporal changes in muscle oxygenation during exercises. Changes in muscle oxygenation and localized O₂ consumption in the quadriceps muscle were measured during sustained isometric knee extension without and with leg-press to the ground exercises. In the former exercise, the level of tissue oxygen saturation (TOS) of the rectus femoris (RF) muscle was found to be lower than that of vastus lateralis (VL) and vastus medialis (VM) muscles. The highest localized O ₂ consumption rate, VO₂, reflecting the localization in distribution of muscle metabolism, was detected in the RF muscle at the initial stage of exercise. As exercise progressed, VO ₂ of the RF muscle decreased whereas that of the VL and VM muscles increased. In contrast, TOS decreased to about the same level for the VL, RF and VM muscles in the latter exercise. Also, VO₂ of all three muscles decreased as exercise progressed. Initial results demonstrated that the SR-NIRS instrument enables measurement of regional differences in muscle oxygenation in the quadriceps muscle during different exercises