Effect of dehydration and a few regimes of rehydration on human performance.

The present study was prompted by the controversy about the effect of heat-induced dehydration on human performance, and the popular Indian belief that it is not advisable to take water immediately after prolonged exertion in the sun. The points investigated were: (i) the effect of dehydration on some aspects of physical and mental performance, and (ii) variation in the post-dehydration performance caused by the timing of rehydration. Dehydration amounting to 2% of body weight did not impair mechanical efficiency while 3% dehydration reduced the endurance time for isometric contraction of extensors of the forearm. The maximum isometric tension and mental performance, measured by proof reading and a choice reaction time experiment, were not affected. The studies suggested that once dehydration had been produced, rehydration or its timing did not make any difference. Analysis of the results in terms of the sequence in which the experiments were done suggested the influence of psychological factors on the performance measured.