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Original scientific paper

Effect of some pharmaca on work output in repetitive physical effort

Z. Bujas ; Institut za medicinska istraživanja i medicinu rada, Zagreb
S. Vidaček ; Institut za medicinska istraživanja i medicinu rada, Zagreb
Mirjana Vodanović ; Institut za medicinska istraživanja i medicinu rada, Zagreb

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page 261-286

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An ever increasing use of pharmaca for stimulation in work or for prevention of fatigue feeling arouses the question of how these pharmaca affect man's actual working capacity. In physical effort, the fundamental problem is in whether pharmacological stimulators increase work output by improving the inner condition of the organism, i. e. by making working effort more economical from the point of view of energy, or whether this increase of working capacity is only the result of a central effect (fatigue feeling inhibition} accompanied by persistent uneconomical use of the energy reserves necessary for a fast and successful recovery in the periods of rest. The studies carried out so far have given no satisfactory answer to this question, mostly owing to inappropriate methods usually applied in such studies. The basic methodological defect was that the efficacy of pharmacological stimulators was usually tested by comparing the maximum work output of a single effort performed under the influence of a pharmacological stimulator up to exhaustion with a maximum work output of a single effort performed without the use of a stimulator. In life, however, one hardly ever works up to exhaustion, and one's work is usually done at intervals, i. e. the phases of action are periodically followed by the phases of rest. For working capacity in the course of a longer period, the rate and degree of recovery in the phases of rest are at least so important as the degree of mobilization of working synergies in the phases of action. In the course of the last five years the authors have studied the effect of various pharmaca on physical work by using the method of repetitive physical effort both of a static (hanging on one's arms) and dynamic (bicycleergometer driving and running on a treadmill) kind. In main experiments three kinds of procedures were used:
a) With a regular pause between successive efforts, the subjects worked several times a day (9-16 times), each time up to exhaustion;
b) The subjects made 10 submaximum efforts with a regular pause between them, and worked up to exhaustion only at the end of the whole experiment; this final maximum effort served as a test of fatigue produced by their previous submaximum efforts;
c) With a regular pause between each effort, the subjects made 4 submaximum efforts first, and then 9 maximum efforts.
The pharmaca used in these experiments were: phenamine (phenyl-izopropilamin sulfas), ritaline (phenyl-/-piperidyl)-acetico-methylic. hydrochloric), preludin (2-phe-nyl-3-methyl-tetrahydro-1,4-oxazin-hydrochlorid), and veronal (5,5 diethylbarbituric acid). They were administered orally either in various phases of the experiment or prior to the experiment.
The results may be summarized as follows:
1. The use of various pharmacological stimulators in. the state of physical freshness and good motivation for work has hardly any positive effect. In such cases the inner normal mobilization of working synergies is high enough for a successful adjustment of the organism to the increased work requirements.
2. Pharmacological stimulators do not seem to be much successful in submaximum efforts either, even if such efforts produce a certain degree of fatigue. A certain posoitive effect of pharmacological stimulators appears to exist only in the final phase of maximum physical efforts.
3. Pharmacological stimulators do not seem to slow down the process of restitution in the phases of rest between successive efforts. It also appears that within certain limits of physical effort the certain increase of work output due to pharmacological stimulators is not brought about at the expense of a greater exhaustion of the organism in a later stage. The energy reserves of the organism seem to be such that even if alarm signals of fatigue feeling are missing, they cannot be affected to such an extent as to cause a significant prolongation of restitution processes.
4. Under the effect of stimulators the subjects regularly feel less tired than in control experiments. The difference in the feeling of pain, localised in active muscles, is specially pronounced, this feeling being considerably milder in the experiments with the use of stimulators. This suggests that the effect of pharmacological stimulators is primarily central, their analgetic action raising the limen of the subjective tolerance of the subject in work.
5. Under the effect of phenamine the pulse frequency is increased before the effort is made, in the course of work, and in the rest intervals. While in successive maximum physical efforts in control experiments the subjects break the work at an ever lower pulse frequency, in the experiments with phenamine the pulse frequency remains on a more or less constant, comparatively high level. However, since there is no correlation between the degree of work output improvement and the difference in the pulse frequency at the end of each effort in the experiment with phenamine and the control experiments, the certain positive effect of phenamine on work output does not appear to be in direct connection with the increased pulse frequency.


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