How come some of us don't sweat during exercise?

Before someone asked me about this question, I actually used sweating as one of the indicators to see if we have worked out hard in class. Sometimes seeing people came into my class in dry outfit and walked out the class dry like a baby diaper (Errr… can I describe the scenario like this?), I really wandered if I had done my part for motivating them to work out harder and sweat a little bit more. My outfit was all wet and dripping in sweat, but how come some people could be so "sweatless" and dry?

Then someone left a comment, posted a question actually, in the posting on "Oh my sweat..." I did some research on it and found out the answer. It was then I realized that I was being ignorant on this issue all this time. Again, I realize the power of this blogging stuff again. I brush up my knowledge by sharing with you what I know, and I acquire new and more knowledge by you asking questions and giving comments. Thank you jeandesign for putting up this question and opened my eyes.

OK, sweating during exercise is an "enjoyable" thing. We generally feel very satisfy when we sweat a lot during workout, and often enough will have a sense of achievement for we have worked out hard. The more we sweat, the more we will feel that we have had a better and more productive workout. However, what if we didn't really sweat during the workout? Was that workout a failure? Had we not exercised hard enough for it to be a productive one? Had we wasted our time in the workout? Were our pores "jammed" or clogged and thus unable to perspire? Were we not fit physically anymore?

To clear all these confusions, we'll first look into why we sweat and later, what is going on when we exercise.

Our body is like an engine that never stops running. And like all engines, it produces heat. The more we move our muscles, the more heat is produced. If the body didn't have ways getting rid of the heat and keeping us cool, we would overheat and collapse within minutes. There are four methods how our body uses to keep us cool:

1. The first method is radiation, where heat radiates out of the skin if the air around us is cooler than our body. Factors important in radiant heat loss are the surface area and the temperature gradient or difference.
   
2. The second method is conduction, which is the transfer of heat by direct contact between our body with other objects, such as swimming in a pool of cold water where the water absorbs our body heat. The rate of conductive heat loss depends on the object(s) that the body has in contact with. Water conducts heat away from the body 25 times faster than air because it has a greater density (therefore a greater heat capacity). In other words, we loss body heat 25 times faster inside water than in dry air land. (Now we know why people like to go into water during those hot weather time.)
   
3. The third method is convection, where moving air cools us down, such like when we stand in front of a fan or when the wind blows. The rate of convective heat loss depends on the density of the moving substance (water convection occurs more quickly than air convection) and the velocity of the moving substance.
   
4. The last method is evaporation, where water from our blood absorbs the heat and rises to the surface of the skin through the sweat glands so it can evaporate creating a cooling effect. The heat loss is converting water from a liquid to a gas. Besides using sweat as a way to remove excessive heat from the body, respiration is another way where air is heated as it enters the lungs and is exhaled with an extremely high moisture content.
   

Methods of Body Heat Transfers

Our body produces heat at all time, even when we are sleeping. In colder conditions, we will not need to sweat as much due to the body using radiation to keep cool. In hotter conditions, sweating is the primary method of keeping us cool due to the surrounding air being hotter than our body. But if humidity presents, sweat cannot evaporate as well and that's why we will see sweat dripping off us. Since in these conditions sweat doesn't evaporate, radiation and convection (remember the moving air?) are used by our body to keep cool.

When we exercise in an air-conditioned room like that in our studio, some of us will not sweat as much because the cold air evaporates our sweat faster. It also sets our body up to use more of the radiation method, meaning our body can deal with the heat created by exercise more easily. It does not mean we are not burning as many calories, because caloric burn is determined by intensity and duration of our exercise, not how much we sweat. We are in fact sweating all the time, just that we just can't see it because it is always evaporating. We will sweat more when there are more people in the studio, or when the air ventilation system is poor.

If it were true that the more we sweat, the more calories we burn during exercise, then it would also be true that we would be burning more calories simply by sitting in a hot, humid room so as to build up a sweat. But this is obviously not the case as the sweat we would be seeing is due only to the conditions of the room not allowing for evaporation for cooling the body. That is, staying inside the sauna room and sweat heavily is because our sweat cannot evaporate and run dry, not because it is helping us to burn more calories. This also dehydrates our body.

Everyone has a different sweating pattern. Gender, age, fitness level and environment contribute to how much we sweat. Women seem to sweat less and start to sweat at higher temperatures than men. People tend to sweat less as they grow old and thus cannot take the heat as well as a younger person but declining fitness levels may have something to do with that. In laboratory experiments where both young and old people were of similar fitness levels, there was no notable difference in their sweating process. However, if given same exercise environment, same intensity level, same length of time for exercise, fitter people usually sweat more and start sweating at a lower body temperature. This is because the function of sweating is to cool the body. A physically fit body cools itself more efficient than one that is unfit.

For those of us who sweat a lot during exercise, it is crucial that we drink more water before, during and after the exercise to rehydrate ourselves. I personally consume about 250 ml water before class, 1,125 ml (the size of my water bottle) throughout a class, and another 250-500 ml after class. You guys know I sweat bullets.

In a nutshell:

Exercise helps to produce more heat; more heat produces more calorie expenditure. We produce the same amount of heat whether exercising in a cold environment or a hot one. Therefore, just because we don't sweat as much in the colder environment does not mean our exercise session was less productive. Remember, for more caloric burn, focus in our intensity (heart rate zones) and/or duration of exercise, not in the amount of sweat.