Fig. 1From: Review of early development of near-infrared spectroscopy and recent advancement of studies on muscle oxygenation and oxidative metabolismCopyright © 2017 Willingham and McCully from Ref. [14]Changes in absorbance (optical density) in accordance to a wavelength. The optical density (absorption) increases at 760 nm when the oxygenated hemoglobin (O2Hb) is deoxygenated (HHb). When blood volume increases, the line shifts to the upper (increase in absorbance)Back to article page