Observation of fatigue unrelated to gross energy reserve of skeletal muscle during tetanic contraction--an application of 31P-MRS.
The mechanism of muscle fatigue was studied by 31P-MRS. During tetanic contraction for 2 minutes(min), the tension measured with a strain gauge and Phosphocreatine(PCr)/Inorganic phosphate(Pi)+ Phosphomonoester(PME) ratio decreased to 31.5 +/- 4.4% of the control value and 0.6 +/- 0.1, respectively. The intracellular pH(pH) also decreased to 6.62 +/- 0.04. Toward the end of the stimulation, the tension decreased to 25.3 +/- 1.9% of the control value. However, during 20min stimulation, the PCr/(Pi+PME) ratio increased to 2.5 +/- 0.5 and the pH to 6.91 +/- 0.04. These results show that muscular fatigue is ascribable not to a decreased level of high energy metabolites required for actomyosin ATPase, but to an increase in the threshold intensity of excitation in excitation-contraction coupling.
Takata
S
S
Department of Orthopedic Surgery, School of Medicine, University of Tokushima, Japan.
Takai
H
H
Ikata
T
T
Miura
I
I
D000818:Animals; D004734:Energy Metabolism; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction; D009132:Muscles / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism; D010725:Phosphocreatine / Q000378:metabolism; D051381:Rats; D013057:Spectrum Analysis; D013746:Tetany
D010710:Phosphates; D010725:Phosphocreatine