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The heat reactions of bantu males in various states of acclimatization

II. The limits of heat stress for a moderate rate of work

Summary

Eighteen highly acclimatized Bantu and four different groups of 20 unacclimatized Bantu worked continuously at 1.0 litre/min oxygen consumption at 72, 82, 86 and 90 °F Effective Temperatures.

Mean rectal temperatures (for the 4 hours) for each of the air conditions were plotted against E.T. and appropriate curves were fitted to the plots. These showed a) that the “average” acclimatized Bantu maintains a constant rectal temperature for the work rate up to 85 ° E.T. b) that the “average” unacclimatized Bantu does this up to 80 ° E.T. These E.T.'s are the limits for “easy” work based uponWyndham et al's 1953 andLind's 1960 criterion of a steady level of rectal temperature for a moderate rate of work.

A different limit for “easy” conditions and a limit for “difficult” conditions was arrived at by plotting of the rectal temperatures of all 18 acclimatized men in one graph and all 20 unacclimatized Bantu in another graph against E.T.'s. One-sided tolerance limits were fitted to these data from which it is possible to estimate the E.T.'s at which 1∶10, or 1∶100, or 1,000 men exceed:

  1. a)

    a rectal temperature of 101 °F, which Wyndham et al. (1965) propose as the physiological limit for “easy” conditions.

    From the Figure 1∶10acclimatized men exceed 101 °F at 88.4 ° E.T.; 1∶100 at 84 ° E.T.; and 1∶1000 at less than 72 ° E.T. 1∶10unacclimatized men exceed 101 °F at less than 72 ° E.T.

  2. b)

    a rectal temperature of 102.5 °, which is proposed as the limit of “difficult” conditions. Here 1∶10acclimatized men exceed a rectal temperature of 102.5 °F at 92.9 ° E.T.; 1∶100 at 92.2 ° E.T.; and 1∶1000 at 91.2 ° E.T. 1∶10unacclimatized men exceed this rectal temperature at 86.4 ° E.T., 1∶100 at 83.0 ° E.T. and 1∶1000 at 76.4 ° E.T.

In order to use this precise, statistical technique for obtaining tolerance limits it is essential to use at least 4 different air conditions so that the shape of the curve expressing the relationship between rectal temperature and E.T.'s can be obtained. It is essential also to use at least 10 subjects at each condition in order to determine the variances but 20 subjects is more profitable. Therefore a minimum sample size of 40 is needed for any population study.

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References

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Wyndham, C.H., Strydom, N.B., Williams, C.G. et al. The heat reactions of bantu males in various states of acclimatization. Int. Z. Angew. Physiol. Einschl. Arbeitsphysiol. 23, 79–92 (1966). https://doi.org/10.1007/BF00716284

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Keywords

  • Oxygen
  • Oxygen Consumption
  • Human Physiology
  • Sport Medicine
  • Statistical Technique