Original scientific paper
Influence of load on the output and on the speed of recovery in static effort
Zoran Bujas
; Institut za higijenu rada Zagreb
Borislav Petz
; institut za higijenu rada Zagreb
Abstract
A series of experiments was carried out by means of a mercury dynamometer on two subjects in order to find out: a) the exact relation between static endurance and load, and b) the speed of recovery after static effort under various loads. The results obtained were as follows:
1. When load increased, static endurance diminished first quickly and then slowing down gradually. The curve representing the relation between endurance and load resembles a hyperbola and can be expressed by the equation: t = a-h - b, where t stands for the time of endurance, h for the load, while a and b are constants.
2. In view of the fact that endurance diminishes quicker than the load increases, the output (th) is greater in work under light than under heavy load. The relation between output and load is a linear one and can be interpolated by the equation: th = a – bh.
3. By comparing endurance in two successive static efforts separated by a pause of unequal length it is possible to observe the progress of recovery in relation to the length of the pause. By lengthening the pause recovery rises, first quickly and then more and more slowly. The results obtained can be b expressed by an exponential equation: o = 1- e-a pb, where o stands for recovery, p for the length of the pause, while a and b are constants, varying according to the circumstances of the experiment.
4. There is a clear difference in the speed of recovery of functional capacities after a single effort under light and under heavy load. The standard time of recovery, necessary for the functional capacity to reach 95% of the initial value, is 4,0 resp. 4,3 times longer after effort under light load. The formula for working out the standard time of recorvery is: os = (3-a) 1-b.
5. Because of considerably quicker disappearance of fatigue after effort under heavy load, the second effort diminishes less then the first as compared with effort under light load.
6. Thus in endurance during second effort the difference in output under light and heavy load decreases. Quicker recovery after work under heavy load partly compensated the decrease of output arising with the increase of the load.
The authors think, that the obtained differences in endurance and in speed of recovery between the static effort under light and heavy loads are conditioned by various mechanisms of fatigue. Fatigue in static effort of a heavy load is primarily of a nervous nature (lowered frequency of efferent nervous impulses, change of subordinational muscle chronaxia, weakened adaptive-trophic activity of the sympathicus on the muscles). Fatigue which appears in static effort under smaller loads is, at first, conditioned almos exclusively by local chemical action, while later on, it is also conditioned by a disturbance in the function of nervous centres.
Keywords
Hrčak ID:
189343
URI
Publication date:
20.12.1950.
Visits: 1.151 *