RELATIONSHIPS BETWEEN FIBER COMPOSITION AND NMR MEASUREMENTS IN HUMANSKELETAL-MUSCLE

The purpose of this study was to examine the relationships between the relative contents of phosphocreatine (PCr), inorganic phosphate (Pi), beta-adenosine triphosphate (ATP), and transverse relaxation time (T- 2) with fiber composition, which determined histochemically in the hum an skeletal muscle. The vastus lateralis muscles of 28 volunteers were subjected to phosphorus nuclear magnetic resonance (P-31 NMR) spectro scopy, magnetic resonance imaging (MRI) and muscle biopsy. Muscle fibe rs were divided into type I and type II fibers using myosin ATPase sta in. A wide range of fiber composition levels were observed in the subj ects (27.3-74.6% type I fibers), The PCr/ATP, Pi/ATP and (PCr+Pi)/ATP ratios were positively related to the percentage of type II fibers (r= 0.695, p<0.001, r=0.429 ,p<0.05 and r=0.773, p<0.001, respectively). T here was no correlation between fiber composition and the PCr/Pi ratio (r0.127, n.s.) or intracellular pH (r=0.305, n.s.). Moreover, no corr elation was found between T-2 and fiber type (r=0.144, n.s.). These re sults suggest that P-31 NMR can detect the differences in relative con tent of phosphates between type I and type II fibers, thereby noninvas ively evaluating fiber composition in human skeletal muscle.