A 31P NMR spectroscopic study was performed in 2 group of volumeers, one group of 14 sedentaries and the other of 8 elite athletes, in order to assess the change of phosphorus high-energy metabolism of the forearm muscles in relation to grasping exercises. Every volunteer was requested to execute a grasping exercise with the dominant arm put in an NMR magnet bore until they reached an all-out state. 31P NMP spectra were obtained initially in the pre-exercise resing state and followed 10 times sequentially for 30 minutes of the post-exercise recovery period. In the sedentaries, the intracellular pH was reduced drastically for 30 minutes of the post-exercise recovery period. In the sedentaries, the intracellular pH was reduced drastically from 7.00$pm$0.01 to 6.06$pm$0.03 in the all-out state and normalized slowly during the recovery period. It took 5.4 minutes to recover 50% of the resting level of pH. The pH in the athletes, however, showed only a minimal decrease after the all-out exercise. The ratio of Pi/$eta$-ATP was 0.49$pm$0.03 in the resting state and increased to 2.05$pm$0.24 immediately after exercise in the sedentaries. The pi/$eta$-ATP ratio of the sedentaries devreased to the normal level during the first 15 minutes of the recovery period, while the change in the athletes was minimal. A decrease of PCr/(PCr+pi) was pronounced in the immediate postexercise period in the sedentaries. However, the change was reversed, although minimal, in the athletes. These data may allow one to explain the differences in muscular high-energy phosphate metabolism between athletes and sedentaries. Based on the degree of exercise we adopted in this study, the main energy source of the sedentaries is thought to be from a nonoxidative cycle and of the athletes, from an oxidative one. NMR spectroscopy, although in its infancy at the present time, is expected to play a major role in the field of muscle physiology and sports medicine for its noninvasiveness and capability to perform in vivo dynamic studies.