CHANGES IN THE HEART-RATE AND ELECTROMYOGRAM BEYOND THE LIMIT TIME OFAN ISOTONIC ISOMETRIC CONTRACTION

Nine men [24.6 (SEM 1.1) years] carried out isometric contractions (IC ) of the right elbow flexors at 50% and 100% of the maximal voluntary contraction (MVC). At 50% MVC they had to maintain IC until the limit time (isotonic IC: IIC50) and beyond for as long as possible (anisoton ic IC: AIC50). At 100% MVC, IC was anisotonic since the decrease in fo rce was immediate (AIC100). Measurements of the force, the integrated electromyogram (iEMG) and the heart rate (f(c)) were made during the e ntire period of contraction. There was a linear relationship between t he iEMG increase and the f(c) increase for IIC50 and AIC100. This rela tionship was not found for AIC50. The role played by the peripheral in formation would seem to have become more important in f(c) regulation when the isotonic IC preceding the anisotonic IC was sufficiently long (submaximal IIC). It would seem that the idea of muscle exhaustion at the limit time was only relative, and depended greatly on the subject 's motivation and his capacity to endure a certain degree of pain.