Exercise-induced muscle modifications: study of healthy subjects and patients with metabolic myopathies with MR imaging and P-31 spectroscopy.
Exercise-induced variations in proton signal intensity at magnetic resonance (MR) imaging and in intracellular pH were studied in the forearm muscles of healthy subjects and patients with muscular glycogenoses. The relative increase in T2 was measured from MR images obtained at 0.5 T, and end-exercise pH was measured with surface coil phosphorus-31 spectroscopy at 2 T. Eight healthy subjects showed a relative increase in T2 ranging from 20% to 44% in the flexor digitorum superficialis muscle and a drop in pH ranging from 0.35 to 1.1. Seven patients with muscular glycogenosis (six with McArdle disease and one with phosphofructokinase deficiency) showed only a slight variation in T2 (0%-17%) and no decrease in pH. Variations in T2 and in end-exercise pH were found to be correlated, perhaps reflecting the stimulation of muscular perfusion caused by acidosis.