Oct. 12, 2010 -- Women need to work harder than men to work up a good sweat, which is necessary to keep the body cool during physical exertion, according to a new study.

Researchers in Japan enlisted 20 women and 17 men to cycle continuously at various intensities for an hour in a room heated to 86 degrees Fahrenheit.

The volunteers were divided into four groups: 10 trained women, 10 untrained women, eight trained men, and nine untrained men. Untrained participants had not done any regular physical activity in the previous three years except for gymnastics lessons. The trained participants had taken part in endurance sports for more than six years.

The sweating rate was measured on five separate body sites.

The study found that the average sweating rate on the forehead, chest, back, forearm, and thigh was significantly greater in trained participants than in those who were untrained.

The amount of improvement in trained participants was greater in men than in women, and this difference increased as the intensity of the exercise increased.

The untrained women had the worst sweating response of all, requiring a higher body temperature than the other three groups to start sweating.

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Evolutionary Reasons for Sweating

Simply put, women apparently need to get hotter than men, by working harder, before they get sweaty, and there’s apparently an evolutionary reason for this, research coordinator Yoshimitsu Inoue of Osaka International says in a news release.

“It appears that women are at a disadvantage when they need to sweat a lot during exercise, especially in hot conditions,” Inoue says. “Women generally have less body fluid than men and may become dehydrated more easily. Therefore, the lower sweat loss in women may be an adaptation strategy that attaches importance to survival in a hot environment, while the higher sweat rate in men may be a strategy for greater efficiency of action or labor.”

The findings may have implications for exercise and heat tolerance in humans, Inoue says, providing insights into why the sexes cope differently with temperature extremes.

Previous research has shown that men have a higher sweat output than women, in part because testosterone is thought to enhance perspiration. Exercise training improves sweating in both sexes, but the degree of improvement is greater in men, becoming even more pronounced as the level of exercise intensity increases, the study shows.

The researchers say that physical training is known to decrease the body’s core temperature threshold for the activation of the sweating response, which works to the advantage of athletes, allowing them to perform longer.

Future studies, Inoue says, will investigate the relationship between reproductive hormones and the sweating response in addition to the effectiveness of different kinds of sweat -- perspiration that evaporates and cools vs. sweat that drips off.

Inoue says that until more research is in, women should take more care than men in hot conditions. “Both men and women can acclimate themselves better to heat if they exercise regularly before a heat wave comes.”

The study is published in the journal Experimental Physiology.