Workout sweat not just a matter of temperature

Summer heat and vigorous exercise can both cause you to break a sweat, but new research suggests that another factor unrelated to temperature may also influence the body's sweat rate.

Researchers in Japan and the U.S. suspect that receptors on muscles that sense motion may play some role in regulating sweating.

The research could help point the way to counteracting how the body's ability to regulate its temperature declines with age, according to the study's lead author.

Receptors called mechanoreceptors on muscles respond to mechanical pressure, a team led by Dr. Manabu Shibasaki at Nara Women's University in Japan explains in an article in the Journal of Applied Physiology.

To see if mechanoreceptors modulate sweating, Shibasaki's team studied seven healthy young men who performed two 20-minute bouts on a tandem reclining exercise bike.

After one session, the participant rested without moving his legs. But after the other exercise session, participants' legs were "passively cycled" by the other person on the tandem bike. This meant that the participant's legs were moving - and mechanoreceptors were being activated - even though he was not exerting any effort at all.

As expected, active exercise increased internal temperature as well as the sweat rate and skin blood flow.

There was no difference in internal and skin temperatures during the two different rest periods, according to the report. But participants sweated more on the arm and chest when their legs were moved by their biking partner than when their legs were still.

The absence of a difference in temperature "strongly suggests" that the stimulation of muscle mechanoreceptors was the main trigger for the extra sweating, according to the researchers.

The findings add to previous evidence that several exercise-related factors affect the sweat rate, Shibasaki's team concludes.

The regulation of heat in the body by sweating and skin blood flow is "mainly controlled" by internal and skin temperature, Shibasaki told Reuters Health. But during exercise, it appears that several non-temperature related factors also influence sweating.

This is important, Shibasaki said, because "exercise-related factors cause sweating before internal temperature elevates."

This increased sweating "could prevent excessive elevation of internal temperature," Shibasaki noted.

The regulation of heat in the body tends to become less efficient as we age, but exercise may help slow this decline, according to Shibasaki.

SOURCE: Journal of Applied Physiology, June 2004.