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March 2023

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

Journal/Book: In: E. MORGAN (Ed.): Chronobiology and Chronomedicine. Vol. II. P. Lang Frankfurt - Bern - New York - Paris 1990 p. 318-321. 1990;

Abstract: Institut für Arbeitsphysiologie und Rehabilitationsforschung der Universität Marburg/Lahn Robert Koch-Strasse 7a D-3550 Marburg/Lahn FRG Rhythmic variations of maximum isometric strength were first reported by Reick et al (1977). The periodicity of these changes was between four and six minutes. Similar variations have been observed during a current study of adaptive responses to isometric muscle training. Forty healthy subjects of both sexes performed 80 isometric voluntary maximum contractions of the left elbow flexors each of six second duration at one minute intervals. Muscular strength was measured by means of a dynamometer (Hettinger 1983). For period analysis the individual curves were smoothed using the formula: xi = (xi-1 + 2xi + xi+1) / 4. and the intervals between maximum and minimum points were calculated from the smoothed curves (as differences between the time points of two maxima or minima respectively). The smoothed curves of the maximum isometric strength measured for seven individuals over the course of 80 contractions are shown in Figure 1. In all test persons the isometric strength decreased in ihe course of the experiment and periodic variations can be seen. The amplitudes of these periodic changes amounted to 5-20 percent of the mean value. However the rhythms seem not to be synchronized to the first contraction. In Figure 2 the frequencies of the minima and the intervals between max'sma of all individual curves are plotted. . . .

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