A mathematical model for analyses of muscle oxygenation measurements using NIR spectroscopy.

Near-infrared spectroscopy (NIRS) enables noninvasive measurement of muscle oxygenation. However, since NIRS does not enable direct measurement of muscle metabolism, it is necessary to analyze the dynamic changes in metabolism during exercise using other methods in order to understand the relationship between NIRS measurements and muscle metabolism. A model of muscle metabolism that is composed of aerobic and anaerobic metabolic systems and O(2) transport to tissue system was developed. Using the model, the temporal profiles of muscle oxygenation during exercise with different intensities (20, 40 and 70% maximum voluntary contraction), measured using NIRS in a single subject, were sufficiently reproduced. In addition, analyses of simulation results of (i) aerobic and anaerobic metabolic systems and (ii) O(2) consumption were performed, and the intensity-dependent differences in the temporal responses during exercise and recovery periods were estimated. The initial results show the usefulness of the model for simulating the kinetics of NIRS measurement data and for systematic interpretation of the relationship between NIRS data and muscle metabolism.