Exercise Protocol and Muscular Fiber Type Composition Dependent Phosphocreatine Recovery in Health and Disease

Differences in phosphocreatine recovery (represented by its time constant, normalized for pHmin) between controls and patients with mitochondrial encephalomyopathies (and migraine with aura) have been detected with 31P-MRS exercise protocols of both low and increasing intensity at low contraction frequency. By employing a protocol of high intensity and high contraction frequency these differences vanish, which may be explained by higher fractions of activated fast twitch fibers and interindividual variations in muscle fiber type composition in controls. Our observations therefore challenge the notion of absolute workload independence of PCr recovery due to different recovery characteristics of fast and slow twitch fibers