Fig. 1.

Spectroscopic measurements during ischemia that yield O₂ uptake, ATP flux, and energy coupling (P/O) in an adult human TA muscle at rest. (Upper) An optical spectroscopic measurement distinguishing Mb and Hb O₂ saturation that is used with their respective in vivo concentrations (Table 1) to determine O₂ uptake during the initial period of ischemia. (Lower) MRS measurement of the dynamics of [PCr]. The [PCr] breakdown during ischemia measures ATP turnover by the cell that must be met by ATP supply from the mitochondria under aerobic conditions.