Don't sweat it

A friend of mine, who happens to be the best ultra-marathon runner in Hong Kong, was going through his paces when he passed a few people hiking. As he flew by, sweat pouring off him, one of the young girls exclaimed he looked like he was swimming. Anyone who has exercised knows that some people sweat buckets while others barely shed a drop. Why is that so?

One of the biggest myths about exercising is that you're out of shape if you sweat. In fact, the opposite is true. Sweating is your body's cooling system. When we exercise, heat production increases, which stimulates the body's 2.4 million sweat glands, producing sweat which evaporates on the skin's surface. Exercise also causes your sweat glands to become larger, so they can release more water, thereby becoming more effective at cooling your body down. So the fitter you are, the sooner and the more you sweat. This ensures you have less risk of overheating. However, if you don't sweat, it doesn't necessarily mean you're unfit. As your fitness increases, so will the rate at which you sweat.

Another indicator that your body is trying to cool down is a red face. This signals you're not able to keep pace with the heat your body's producing. In this case, your body directs more blood to the skin to cool you down. Of course, there could be a genetic factor that predisposes your face to go red. However, improving your fitness level will cause you to produce more sweat earlier and stop you going red.

Your body's ability to cool itself occurs regardless of where you're exercising. If you become hot, you'll sweat. Even in an air-conditioned room or ice-skating on a frozen pond, if your body starts to heat up, then you'll perspire. We can even sweat in water. When outside temperatures are high, we retain more heat, thereby producing perspiration. High humidity causes you to perspire more because it reduces the rate at which perspiration can evaporate.

The amount of sweat produced also depends on the level of intensity of the exercise. During light to moderate activity, most fit people will sweat approximately one cup every 20 minutes. That's about four times as much as a horse and almost twice as much as a camel. World-class athletes can sweat about four litres of water every hour.

As sweating affects our cardiovascular system, it's important to replace the fluids we lose while perspiring. Luckily, for healthy people there's a safety zone of up to 24 hours to replace this lost fluid. A good way to judge fluid lost through sweating is by weighing yourself. For every kilogram lost, you should drink at least a litre of fluid. All that sweat is just a healthy sign that your body's cooling system works efficiently.