Work Performance After Dehydration: Effects of Physical Conditioning and Heat Acclimatization

Abstract

Three groups of five men each were dehydrated overnight in the heat (115℉) on two occasions (D₁ and D₂) to approximately 5.5% of their starting body weight. During the 3-week period between D₁ and D₂, one group (AC) was acclimatized to heat and physically conditioned, the second group (C) was physically conditioned and the third group (S) remained sedentary. The response to work after dehydration was assessed by the following criteria: pulse rate (P), rectal temperature (T_r) and maximal oxygen intake (Max. Vo₂). Pulse rates during and after walking and after running were elevated with dehydration. This elevation was reduced in groups AC and C at D₂ as compared to D₁, but not in group S. An elevation in T_r with walking also occurred with dehydration, but this elevation was not significantly different at D₂ as compared with D₁ in any group. Physical conditioning elicited an elevation in Max. Vo₂ (group AC and C), but the elevation was no greater in group AC than in group C. Dehydration was associated with an equal decrement in Max. Vo₂ at D₁ and D₂ in all groups, but the conditioned men (AC and C) maintained a relatively higher Max. Vo₂ than group S. Thus, physical conditioning was associated with enhanced work performance during dehydration (assessed by the above criteria), whereas acclimatization to heat did not appreciably supplement this effect. Submitted on September 3, 1957