Periodic changes of the isometric strength in the course of 80 maximum voluntary contractions

Journal/Book: J. interdiscipl. Cycle Res. 19: 174-175 (1988). 1988;

Abstract: (Institut für Arbeitsphysiologie und Rehabilitationsforschung der Universität Marburg/Lahn Marburg/Lahn FRG) Forty healthy subjects of both sexes performed 80 isometric maximum contractions (each of 6 sec duration with 1 min intervals) of the elbow flexors. Muscular strength was measured by means of a dynamometer. The strength values of each contraction were integrated. For period analysis the individual curves were smoothed using the formula xi =(xi-1 + 2xi + xi+1) : 4. The maximum and minimum intervals were calculated from these smoothed curves. As expected the mean isometric strength decreased significantly to 65-70% of the initial value. However the decrease was interrupted by phasic increases of the strength values. The amplitudes of these periodic changes amounted to 5-20%. The period analysis showed that period durations of 5 min were dominating (range 4-10 min). These results coincide with former investigations of Rieck et al. (1977) who reported 4-6 min periods of the maximum isometric strength in the course of repeated contractions. However the periodic variations of the strength curves in our study were nog synchronized by the first contraction. As mechanism periodic changes of the vigilance of the subjects or of the local metabolism have to be considered. . . .

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