Original scientific paper
Influence of preliminary effort on the sensation of strain and on static endurance
Zoran bujas
; Institut za higijenu rada Zagreb
Borislav Petz
; institut za higijenu rada Zagreb
Abstract
The authors examined (a) the phenomenon of the successive contrast in the sensation of strain and (b) the influence of a preliminary more and intense effort on static endurance under lighter load. Static work was carried out on Henry's mercury dynamometer.
(a) After a determined static pressure (raising of mercury to 30 cm) had been carried out under the control of eyes, the subjects (N = 50) attempted to repeal the same pressure with closed eyes. In one series of experiments, this occurred after intense static work, while in another without preliminary load. The results show that after work the standard pressure is underestimated i. c. mercury rises to a higher level than foreseen. This contrast influence of preliminary effort is the greater the 'more intense the effort was. The authors consider that this phenomenon of successive contrast is called forth, in addition to mechanisms put forward by various authors (changes in the sensitivity of receptors, mental attitude. persistence of excitement in nerve centres) also by some other factors - in the first line by an increased tonus of formerly active muscles and by activation of work synergies. (b) The maximal term of endurance under light static load was compared on two subjects with the term of endurance under the same load but offer previous intense static effort of various duration. It was found in both subjects that previous intense work of shorter duration increases endurance in a lighter static effort (for 18,2% in subject A, and for 19,4% in subject B). However, if preliminary work lasted longer, the positive contrast influence is lost and endurance decreases during work under light load. Combined work under heavy and light load gives, on the entire time scale, a greater output (product of load and of duration of effort) than that of the maximal output under only light load, although under normal conditions output diminishes rapidly when load increases. The sensation of relief after partial rapid release from lead is therefore connected with a real improvement of physiological conditions under which further work is done. The authors consider this phenomenon lo be caused, in the first place, by a rapid mobilisation of work synergies which -during transition to a lighter load- makes a more economical work possible on this functional level than without such a preliminary effort. As the role of the nerve is dominant, in static work under heavy load it is understandable that preliminary intense work can, by stimulating nerve centres, call forth a rapid mobilization of synergies and thus shorten the energetically expensive and land stage of »warming up« during work under light load. In connection with these results it would be interesting to re-examine the rule that the best way of »introduction to work« is an activity imitating the work as to intensity, rhythm and form; or whether it would not -as these experiments seem to indicate- be preferable to make the preliminary work shorter but of much greater intensity.
Keywords
Hrčak ID:
187565
URI
Publication date:
12.6.1952.
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