Near-infrared spectroscopy (NIRS) has been shown to be one of the tools that can measure oxygenation in muscle and other tissues in vivo. This review paper highlights the progress, specifically in this decade, that has been made for evaluating skeletal muscle oxygenation and oxidative energy metabolism in sport, health and clinical sciences. Development of NIRS technologies has focused on improving quantification of the signal using multiple wavelengths to solve for absorption and scattering coefficients, multiple pathlengths to correct for the influence of superficial skin and fat, and time-resolved and phase-modulated light sources to determine optical pathlengths. In addition, advances in optical imaging with multiple source and detector pairs as well as portability using small wireless detectors have expanded the usefulness of the devices. NIRS measurements have provided information on oxidative metabolism in various athletes during localized exercise and whole-body exercise, as well as training-induced adaptations. Furthermore, NIRS technology has been used in the study of a number of chronic health conditions. Future developments of NIRS technology will include enhancing signal quantification. In addition, advances in NIRS imaging and portability promise to transform how measurements of oxygen utilization are obtained in the future.

The inhomogeneity of tissue structure greatly affects the sensitivity of tissue oxygenation measurement by reflectance near-infrared spectroscopy. In this study, we investigated the influence of a fat layer on muscle oxygenation measurement by in vivo tests and Monte Carlo simulation, and we propose a method for correcting the influence. In the simulation, a three-dimensional model consisting of the epidermis, dermis, fat, and muscle layers was used. In in vivo tests, measurement sensitivity was examined by measuring oxygen consumption of the forearm muscle and the peak-to-peak variation of oxygenation in periodic exercise tests on the vastus lateralis using a newly developed multisensor type of tissue oximeter. Fat layer thickness was also measured by ultrasonography. The correction curve of measurement sensitivity against fat layer thickness was obtained from the results of simulation and in vivo tests. The values of corrected oxygen consumption were almost the same and had less variation between individuals (0.13±0.02 ml 100 g−1 min−1) than did the uncorrected values (0.08±0.04 ml 100 g−1 min−1).

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Abstract. The best way to assess fetal condition is to observe the oxygen status of the fetus (as well as to assess the condition of infants, children, and adults). Previously, several fetal oximeters have been developed; however, no instrument has been utilized in clinical practice because of the low-capturing rate of the fetal oxygen saturation. To overcome the problem, we developed a doctor's finger-mounted fetal tissue oximeter, whose sensor volume is one hundredth of the conventional one. Additionally, we prepared transparent gloves. The calculation algorithm of the hemoglobin concentration was derived from the light propagation analysis based on the transport theory. We measured neonatal and fetal oxygen saturation (StO 2 ) with the new tissue oximeter. Neonatal StO 2 was measured at any position of the head regardless of amount of hair. Neonatal StO 2 was found to be around 77%. Fetal StO 2 was detected in every position of the fetal head during labor regardless of the presence of labor pain. Fetal StO 2 without labor pain was around 70% in the first stage of labor and around 60% in the second stage of labor. We concluded that our new concept of fetal tissue oximetry would be useful for detecting fetal StO 2 in any condition of the fetus.

Skeletal muscle deoxygenation abnormalities were observed during dynamic cycling exercise in early post-MI patients. These abnormalities were related to impaired peak aerobic capacity in early post-MI patients.