Fig. 4. Diagram of the reciprocal changes in phosphocreatine level ([PCr]) and [ADP] that occur via the creatine kinase reaction during exercise (A) and the effect of the rise in [ADP] with exercise (red curve and arrowhead) on mitochondrial oxidative phosphorylation (B). Data in A are unpublished results from human ankle dorsiflexor muscles, and data in B are from isolated mammalian heart mitochondria (Mootha et al., 1997).