Near infrared spectroscopy: from the "black box to the ice arena". Symposium introduction.

In the past, near infrared spectroscopy (NIRS) has been mostly used to investigate oxidative metabolism in pathophysiology (Belardinelli et al., 1995; Ferrari et al., 1997). However, its application to exercise has increased exponentially over the past 15 years. NIRS is a noninvasive optical technology used to estimate tissue oxygenation by applying the physical principles associated with light absorption and scattering in the medium under investigation. NIRS is based on the differential properties of oxygenated and deoxygenated (Hb) and oxygenated and deoxygenated myoglobin (Mb), and cytochrome-c oxidase (Cytox) in selected tissue, as these chromophores have the capacity to absorb light. In the near infrared light range of 700–1000 nm, the absorbed light by oxygenated Hb and Mb (Hb/Mb-O2) and deoxygenated Hb and Mb (Hb/Mb-H+) display distinct absorption spectra. By measuring the difference in tissue absorbency of these spectra, we can obtain a representation of the relative change in tissue oxygenation. Thus these changes in tissue absorbency have also been related to muscle oxygen saturation, as muscle oxygen saturation represents a balance between O2 supply and O2 consumption in the capillaries, arterioles, and venules (Belardinelli et al., 1995; Chance et al., 1992). Although NIRS appears to be a suitable tool for providing value insight into the heterogeneity of local tissue (skeletal muscle and cerebral tissue) saturation, the use of NIRS to monitor oxygen saturation and blood volume changes in exercising tissue has been questioned (Costes et al., 1996; Hicks et al., 1999; MacDonald