Low Doses of Melatonin and Diurnal Effects on Thermoregulation and Tolerance to Uncompensable Heat Stress


  1. McLellan, T.M.
  2. Frim, J.
  3. Bell, D.G.
  4. Gannon, G.A.
  5. Zamecnik, J.
  6. and others
Corporate Authors
Defence and Civil Inst of Environmental Medicine, Downsview ONT (CAN)
The wearing of NBC protective clothing in hot environments imposes a severe thermal burden. If feasible, one option to help reduce the heat strain is to provide cooling close to the skin surface. Present-day technologies include both liquid (L) and air (A) cooled vests that have been shown to be effective when protective clothing is worn during very light exercise. The present study involved the comparison between liquid and air cooling systems during both light (L) and heavy exercise (H). Eight subjects performed 6 trials for a maximum of 3 hours at 40C and 30% relative humidity that involved L or H exercise with no cooling (N), L or A cooling. Up to 350 W of cooling was delivered to the NBC ensemble during the heavy exercise with L cooling. Approximately one-half of this cooling power (175 W) was evident as an increased heat flow from the body. The cooling power of the air vest could not be determined since outlet air temperature could not be measured. Tolerance times were extended from 100 min during LN (light exercise with no cooling) to the maximum of 3 hours with either L or A cooling. During H exercise, tolerance times increased approximately 150% form 60 min with N to 150 min with either L or A cooling. There was not difference in the cooling effectiveness between L or A. TRUNCATED
Rectal temperature;Circadian rhythm
Report Number
DCIEM-98-P-51 — Reprint
Date of publication
01 Jul 1999
Number of Pages
Reprinted from
J Appl. Physiol, vol 87, no 1, 1999, p 308-316
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