Ask an expert

05 Jan 2005

Sweating while exercising
I'm looking for information on sweating whilst exercising. I am quite fit and sweat a lot, there is no odour to the sweat at all. Can you give me an explanation as to how the body works in this department. Thank you
Answer 416 views

01 Jan 0001

Hi Renate

The full explanation is very complex, and requires quite a bit of background and explanation, and so the best thing you can do is check out a physiology text book on the subject, where you can go from the top. i will try to explain the basic concepts, but details you may need to fill in from elsewhere.

As you may know, sweating is very important during exercise because it is through the evaporation of sweat that you are able to lose heat and keep the body temperature down. therefore, no sweating means overheating, so it is good to sweat a lot. Sweat is produced in the sweat glands, which are stimulated during exercise by the sympathetic nervous system. This is a divison of your nervous system which kicks in to prepare you for exercise and for anything requiring activity or action. So, that's why you sweat when you are nervous. It's the same system that gives you butterflies, makes your hands clammy, your pupils dilate, and there is a hold range of other responses that occur all of which get you ready for action. Sweating is one of these.

What happens with training is that your sweat glands become better. that is, the body is able to use more of them, and consequently, the volume of the sweat increases. This explains why fit people often seem to sweat more.

Another change, one that you often can't measure, but that you touched on, is that the sweat actually changes in composition. Sweat always contains salts, sodium chloride, potassium, magnesium etc. That's why the sports drinks all claim to replace the electrolytes (or salts) lost in sweat. The truth is that the sweat content is actually pretty low - you can't ever lose salt from sweating alone, unless you have some disease. The fact is that there is just so little sodium in the sweat. However, with training, what happens is that the salt content of the sweat decreases - this happens as a result of the body becoming more sensitive to a certain hormone, aldosterone. This is a complex mechanism, I'm not sure i'll go into it, but the short version is that this hormone is salt-conserving, and so if the body gets more sensitive, then it absorbs back more salt and so the salt in sweat decreases. This may help to explain why sweat is sometimes odourless.

Finally, a question of physics. even as you sit and read this, you are probably sweating - however you don't notice it because it is all evaporating right away. therefore, it is called insensible perspiration. Only when the humidity is higher than allows the sweat to evaporate, do we even notice sweat. That's why people who are accustomed to exercising out doors battle in gyms - the humidity is higher and there are no fans to help in cooling and they think that they are sweating more. The truth is that they are sweating probably about the same, but less is evaporating.

Hope this clears up some of the questions
The information provided does not constitute a diagnosis of your condition. You should consult a medical practitioner or other appropriate health care professional for a physical examination, diagnosis and formal advice. Health24 and the expert accept no responsibility or liability for any damage or personal harm you may suffer resulting from making use of this content.
Voting Booth
Have you entered our Health of the Nation survey?
Please select an option Oops! Something went wrong, please try again later.
33% - 9380 votes
67% - 19432 votes