Predicted Heat Strain (PHS) model and the sweat loss in an extremely hot climate

• Introduction: The aim was to study if the evaporative water loss can be predicted enough accurately for hydration recommendations by ISO 7933 – Predicted Heat Strain (PHS) model during a student laboratory exercise in an extremely hot environment.Method: Twelve young healthy students (8 males and 4 females), unacclimatized to heat, were exposed in a climatic chamber at 50˚C, 30% relative humidity and 0.4 m·s-1 air velocity for 45 minutes. They had a mean (SD) age of 25.1 (2.6) years, height 175.6 (6.9) cm, weight 72.3 (11.0) kg, VO2max 54.9 (6.5) mL·min-1·kg-1, and HRmax 194 (6) bpm. The men and women performed bicycling for 6-minutes at workloads of 150 and 100 Watts (W), when the metabolic rates (M) calculated found 363 and 290 W·m-2, respectively. Moreover, the students did step test at 60 steps·min-1 for 5-minutes with estimated M being 215 W·m-2. They were standing most of the time (34 min) (M = 80 W·m-2). Time weighted average M for males and females were 133 and 123 W·m-2, respectively, for the whole exposure duration. Clothing insulation, Icl = 0.4 clo and moisture permeability index, im = 0.42 were input to PHS model simulation. The actual water loss by evaporation was determined by subject’s dressed body weight difference before and after exposure.Results: The actual mean (SD) total water evaporated was 461.3 (176.7) g. The predicted total water loss was 427.4 (39.2) g by the PHS model. There was no significant (p = .514) difference between the actual and the predicted water loss. However, the original estimation of evaporative sweat was found only 270.1 g.Conclusions: These results suggest that it is challenging to predict the water loss in continuous extreme heat exposure at 50˚C using ISO 7933 – PHS model. It should be used cautiously to predict the dehydration, and plan for drinking in extremely hot climates.

Subject headings

TEKNIK OCH TEKNOLOGIER  -- Annan teknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Other Engineering and Technologies (hsv//eng)

Keyword

Water loss

sweat loss

Prediction models

Dehydration

Recommendation

Publication and Content Type

kon (subject category)

ref (subject category)