Effects of Dehydration, Hypohydration, and Hyperhydration on Tolerance During Uncompensable Heat Stress


  1. McLellan, T.M.
  2. Cheung, S.S.
  3. Latzka, W.A.
  4. Sawka, N.
  5. Pandolf, K.B.
  6. and others
Corporate Authors
Defence and Civil Inst of Environmental Medicine, Downsview ONT (CAN)
The present study examined the effects of dehydration from prior exercise on subsequent exercise tolerance time (TT) that involved wearing nuclear, biological, and chemical (NBC) protective clothing. It was hypothesised that TT would be reduced in the dehydrated state. Ten men undertook continuous treadmill walking at 4.8 km - h 1(-) at 35C and 50% relative humidity; wearing NBC clothing while euhydrated (EU) or dehydrated (D) by 2.3% of body weight. Hydration status had no impact on thermoregulatory or cardiovascular responses during exericse. Also rectal temperature at exhaustion did not differ between EU (38.52) + or - 0.39C) and D (38.43 + or - 0.45C). Exercise TT during this uncompensable heat stress was reduced significantly for D (47.7 + or - 15.3 min) compared with EU (59.0 + or - 13.6 min). It was concluded that prior exercise leading to levels of dehydration to 2.3% fo body weight, together with subsequent fluid restriction during exposure to uncompensable heat stress, impaired TT while wearing the NBC protective clothing. The integration of these findings together with other comparable studies that have examined the influence of hypo- and hyperhydration on TT while wearing NBC protective clothing revealed that hydration status has less effect on TT as the severity of uncompensable heat stress increases.
Hypohydration;Temperature regulation;Rectal temperature;Fluid replacement;Hyperhydration
Report Number
DCIEM-98-P-43 — Reprint
Date of publication
01 Jan 1999
Number of Pages
Reprinted from
Can J. Appl. Physiol, vol 24, no 4, 1999, p 349-361
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