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Physiological and metabolic responses to work in heat with graded hypohydration in tropical subjects

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Studies were conducted on 25 healthy male volunteers aged 20–25 years drawn randomly from the tropical regions of India. The subjects initially underwent an 8 day heat acclimatization schedule with 2 hours moderate work in a climatic chamber at 45° C DB and 30% RH. These heat acclimatized subjects were then hypohydrated to varying levels of body weight deficits, i.e. 1.3±0.03, 2.3±0.04 and 3.3±0.04%, by a combination of water restriction and moderate exercise inside the hot chamber. After 2 hours rest in a thermoneutral room (25±1° C) the hypohydrated subjects were tested on a bicycle ergometer at a fixed submaximal work rate (40 W, 40 min) in a hot dry condition (45°C DB, 30% RH, 34° C WBGT). Significant increases in exercise heart rate and oral temperature were observed in hypohydrated subjects as compared to euhydration. Sweat rate increased with 1% and 2% hypohydration as compared to euhydration, but a significant decrease was observed with 3% hypohydration. Na+ & K+ concentrations in arm sweat increased with increase in the level of hypohydration. Oxygen consumption increased significantly only when hypohydration was about 2% or more. It appears that the increased physiological strain observed in tropical subjects working in heat with graded hypohydration is not solely due to reduced sweat rates.

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Pichan, G., Sridharan, K. & Gauttam, R.K. Physiological and metabolic responses to work in heat with graded hypohydration in tropical subjects. Europ. J. Appl. Physiol. 58, 214–218 (1988). https://doi.org/10.1007/BF00636629

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Key words

  • Dehydration
  • Heat stress
  • Sweat rate
  • Sweat electrolytes
  • Ventilation
  • Metabolic rate