³¹P magnetic resonance spectroscopy provides the possibility to obtain bio-energetic data during skeletal muscle exercise and recovery. The time constant of phosphocreatine (PCr) recovery (_PCr) has been used as a measure of mitochondrial function. However, cytosolic pH has a strong influence on the kinetics of PCr recovery and it has been suggested that _PCr should be normalized for end-exercise pH. A general correction can only be applied if there are no intersubject differences in the pH dependence of _PCr. We investigated the pH dependence of _PCr on a subject-by-subject basis. Furthermore, we determined the kinetics of proton efflux at the start of recovery. Intracellular acidosis slowed PCr recovery and the pH dependence of _PCr differed among subjects, ranging from -33.0 to -75.3 s per pH unit. The slope of the relation between _PCr and end-exercise pH was positively correlated with both the proton efflux rate and the apparent proton efflux rate constant, indicating that subjects with a smaller pH dependence of _PCr have a higher proton efflux rate. Our study implies that simply correcting _PCr for end-exercise pH is not adequate, in particular when comparing patients and controls, as certain disorders are characterized by altered proton efflux from muscle fibers.