Low performance of fatigued skeletal muscle accompanies large difference in the state of water : test of hypothesis.

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Repetitive contraction of frog muscle elicited by tetanic nerve stimuli induced general retardation of transverse relaxation process of muscle water observed with NMR. Similar change was observed in lumbrical muscle of rat stimulated directly. Therefore, similar change is expected to accompany muscle fatigue in humans. To elucidate the entity of this change in water state, we performed experiments on myofibril suspension. Myofibrils affected water molecules far from its surface. The fraction of this suppressed water increased with myofibril concentration in a temperature dependent manner. The dependency indicated the interaction between water and muscle is the hydrophobic interaction. The interaction also affected physical property of water affecting the sedimentation limit for myofibrils. In the model muscle fiber of fatigued muscle induced by BTS and BDM, there is a fraction of stiffness that is not linked with contractile force development. This stiffness in muscle may be related with the fatigue-induced change in water state. As for the intramuscular water components, we assigned subcellular localization of water components distinguished by the transverse relaxation. To mimic the water milieu in muscle, we succeeded to develop hydrocarbon solution of low to intermediate molecular weight. Combined with the molecular dynamics simulation, we could estimate the molecular events accompanying fatiguing process of skeletal muscle. From these results, we proposed a sensitive method to detect fatiguing process in human skeletal muscle. That is, eliminating slowly relaxing part of the NMR signals from skeletal muscle, one can depict intracellular water components as a density map. Fatigue-induced retardation of the transverse relaxation process is considered to increase CPMG visible water as fatiguing process proceeds.