31P-MRS of quadriceps reveals quantitative differences between sprinters and long-distance runners.

Phosphorus-31 nuclear magnetic resonance spectroscopy (31P-MRS) has been used to characterize the spectral pattern of quadriceps muscle at rest for sedentaries (N = 10), sprinters (N = 12), and long-distance runners (N = 10). Intracellular pH (pHi), phosphocreatine (PCr), inorganic phosphate (Pi), phosphodiesters (PDE), adenosine triphosphate (ATP) and total phosphate (Pt), defined as the sum of the areas of PCr, PDE, Pi, and 3 times the beta-ATP resonances, were obtained from all spectra. The pHi and ATP/Pt ratio were the same in the three groups of people studied. The PCr/Pi and PCr/Pt ratios were significantly lower and the Pi/Pt ratio was significantly higher for long-distance runners than for sprinters and sedentaries, while the PDE/Pt ratio was significantly lower for sprinters than for sedentaries and long-distance runners. Furthermore, the PCr concentration for sprinters and sedentaries was significantly higher and the Pi was significantly lower than for long-distance runners. The results obtained in this study can be explained by the accepted differences in fiber type composition between sprint and endurance athletes. We suggest that 31P-MRS at rest could be used to monitor noninvasively the individual adaptive response to training in the metabolic characteristics of the athlete muscle fiber.