The Hex measures muscle oxygenation (SmO2) by shining light into the muscles and detecting the amount of light reflected back. Light in the near-infrared wavelength range is used by the Hex to penetrate the muscle and is either absorbed or scattered by the tissue. The wavelengths of light are chosen specifically to be sensitive to the absorption of oxy-hemoglobin (HbO2) and deoxy-hemoglobin (Hb). By measuring how the light is absorbed, the concentrations of HbO 2 and Hb within the muscle can be found. The SmO2 is then calculated by taking the ratio of HbO2 to the total hemoglobin (HbT = HbO2 + Hb).