Heat tolerance in women--reconsidering the criteria

Exertional heat stroke (EHS) is the most dangerous heat-related injury. EHS may be followed by a state of heat intolerance. The Israeli Defense Forces (IDF) performs heat tolerance tests (HTT) to all heat injury victims 6-8 wk following injury as part of the "return to duty" process. The HTT protocol and normal values are based on vast experience with young healthy men. Over the last several years an increasing number of female soldiers have been joining combat units. Heat injuries and, thus, HTT among women have become more frequent. Due to potential gender-related physiological and thermoregulatory differences, we examined the necessity for validating the HTT protocol for women.

Retrospective physiological data from our database on heat injuries and HTT between the years 2008-2010 was compared between 9 female subjects and 170 male subjects who had similar background characteristics.

Defining heat intolerance as peak rectal temperature > 38.5 degrees C, peak heart rate > 150 bpm, or the inability to reach equilibrium in these values, we diagnosed 67% of the female subjects as heat intolerant. In the male subjects, only 26% were diagnosed as heat intolerant using the same criteria.

Using the standard HTT criteria, women are more frequently diagnosed as heat intolerant than men. Further studies should be performed in order to re-evaluate the normal values for a "female HTT" in order to optimize the process of safe return to duty of female heat injury victims and to minimize false positive results among female soldiers.