Accuracy improvements of NIRS and investigation of muscle oxidative metabolism

Abstract

In the rst part of the thesis, the e ect of fat layer on continuous wave near infrared spectroscopy (cw-NIRS) measurements were investigated in detail, both in terms of underestimation error (caused by homogeneous medium assumption) and crosstalk between chromophores because of homogeneous medium assumption and wavelength dependence of mean partial path length in the muscle layer. These errors have been investigated by Monte Carlo simulations with a skin-fat-muscle layered tissue model for a two wavelength system. The errors have been found to be higher for thicker fat thicknesses. A correction algorithm was proposed with the use of wavelength dependent partial path length in the muscle layer derived with Monte-Carlo simulations. Two detector cw-NIRS system was also analyzed and compared with 1-detector cw- NIRS system. The performance was promising but true assumption of initial optical coe cients of the layers poses a challenge for the performance. Muscle metabolism, fatigue and endurance was examined with usage of three simultaneous measurement modalities: cw-NIRS, SEMG and force-time for isometric hand grip exercise. The study revealed some physiological processes related to fatigue. A highly valued and statistically signi cant correlations were found between sEMG and cw-NIRS derived parameters especially at 50% maximal voluntary contraction along with biometrics for endurance prediction. These information could be important in sports applications, ergonomics, physical medicine and rehabilitation to monitor the recovery with objective parameters.|Keywords: Near infrared spectroscopy, Continuous wave near infrared spectroscopy, Monte Carlo simulations, Light propagation in tissue, Muscle oxidative metabolism, Tissue oxygenation, Endurance, Fatigue, Surface electromyography.