YOU DECIDE TO head to the gym with your best friend for a 30- or 45-minute cardiovascular workout. Shortly after arriving and hopping   on the treadmill, you are dripping wet with sweat, but your friend has barely reached the point where her skin is glistening from perspiration. You wonder if it is because you are working out at a higher intensity. Nope—you are both running at 7 miles an  hour.

Maybe it’s because you are bigger. Again, no—you both are approximately the same height and weight.

Maybe it’s because you are in better shape. You do recall reading on the Internet that individuals who are in better shape sweat more. But that doesn’t make sense, because your friend works out much more than you do, and she even runs road races—and you don’t.

In reality, it could simply be that you sweat more easily than your friend!

Sweat is primarily water with a bit of sugar, salt, ammonia and urea. Each person has 2–4 million sweat glands. Women generally have more sweat glands than do men, but women’s sweat glands are less active.

The greatest concentration of sweat glands in humans is on the bottoms of our feet, on the palms of our hands and in our armpits. Many people think sweat smells bad, but sweat is relatively odorless. Sweat mixing with bacteria on the skin creates the strong and sometimes-repulsive odor we smell after someone has been sweating.

Sweat is one of the ways we dissipate heat to cool our bodies, especially during exercise. Exercise raises body temperature, prompting increased sweating. Interestingly, some animals—dogs, for example—don’t have sweat glands. They pant to cool down, losing heat through their mouths and tongues.

Sweating rates in people vary a great deal. As in the scenario above, some people sweat easily and sweat a lot. Others can engage in intense physical activity and sweat very little.

Does our state of physical fitness have a bearing on how much we sweat? A recent article published in the American Journal of Physiology by Jay and colleagues (2011) examined sweat rates in research participants based upon Vo2 peak, a measure of how much oxygen a body can take in and use during exercise. Generally speaking, individuals who are in better shape have  greater Vo2  peak.

Following the study the authors concluded, “The present study clearly demonstrates that large differences in Vo2 do not influence changes in core temperature or sweating during exercise in a neutral climate.”

Being in great physical shape didn’t affect sweating rates in research participants; however, as we up our training regimen and improve our physical conditioning, our bodies become more efficient at retaining electrolytes that are important for performance.

So don’t feel bad if you sweat more than your friend or she sweats more than you do. The important thing is that you get out there, are active and have fun doing it!

Jay, O., Bain, A., Deren, T., Sacheli, M., and Cramer, M. Large differences in peak oxygen update do not independently alter changes in core temperature and sweating during exercise. American Journal of Physiology (2011), Vol 301, pp. 832-841.