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In the nineteenth century, there was a quaint notion that men perspired when they exercised, but women did not.

Fit women sweat less profusely than fit men

In the one hundred-plus years since the Victorian era, women have entered activities once reserved for men, ranging from military service to construction work to working out in the gym. The notion that somehow women do not sweat, however, has persisted, and was recently addressed in the journal Experimental Physiology. Japanese scientists have discovered that fit women perspire quite differently from fit men, and differently from unfit people in both sexes.

To investigate patterns of perspiration in both the fit and the unfit, scientists at Kobe University and Osaka International University had groups of fit and unfit men and women ride exercise bikes in a humid room heated to 86 degrees F (30 degrees C). At first the ride was done at a very leisurely pace, timed to correspond to 30 per cent of maximum effort. Then the cyclists were forced to speed up to 50 or 65 per cent of their maximum effort, measured in terms of how many liters of oxygen the cyclists breathed every minute.

Throughout the study, the researchers observed how much sweat the volunteers produced on their backs, chests, forearms, thighs, and foreheads. The research team also measured how many sweat glands were active at each site, and how much sweat was released from each gland.

Not surprisingly, the research team found that fit men sweated more than fit women. Fit women, the researchers found, simply could not rev up sweat production to keep pace with the warmth and humidity of the exercise room. Unfit women were even more “hot and bothered” by their exercise experience.

Fit women sweat more profusely than unfit women

Unfit women, on the other hand, had the most difficulty with heat and humidity of all four groups. Women who were not in good shape were eventually able to start sweating to cool down their body's core temperature, but only after their inner organs approached the critical temperature of 104 degrees F (40 degrees C).

If body temperature passes 104 degrees F, the brain simply shuts down the motor cortex until the temperature begins to go back down. If you were on an exercise bike when this happened, your legs would begin to feel rubbery and you would then fall off your bike until sweating brought your core temperature back to normal. Sweating prevents the core temperature from getting this high.

Estrogen works against the ability of perspiration to prevent heat injury. Women who have higher estrogen levels sweat less efficiently who have lower estrogen levels. That means an unfit woman who is on hormone replacement therapy needs to be very careful to avoid exercising in extreme heat. Physical fitness reduces the effect of estrogen, but it is not enough to completely compensate for a woman's adaptation to physical activity at lower temperatures.

Testosterone increases resistance to heat. The more testosterone in a man's body, the more heat he can handle. One of the best ways for men to maintain their testosterone levels is simply to avoid accumulating body fat. Fat cells convert testosterone into estrogen in both men and women, but their effect is more likely to be felt in men.

  • Ichinose-Kuwahara T, Inoue Y, Iseki Y, Hara S, Ogura Y, Kondo N. Sex differences in the effects of physical training on sweat gland responses during a graded exercise. Exp Physiol. 2010 Oct,95(10):1026-32. Epub 2010 Aug 9.
  • Photo courtesy of Robert Hensley by Flickr : www.flickr.com/photos/roberthensley/7643955476/

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