Kenneth Gardner

Dear Mr. Gardner,

I recently purchased a sauna suit for exercising; the material is all plastic. Is it safe to exercise in this suit without clothing underneath or what? I have found that under normal circumstances, when I am exercising, I do not perspire as much, but when I use the sauna I perspire a whole lot. My main aim is to lose weight.

Response to reader

Exercising in your sauna suit will insulate your body and reduce the effective surface area for heat loss. When you are exercising it is important to minimise your clothing to provide an optimal skin surface area from which evaporation can occur.

Ideally, exercise clothing should allow your body to cool itself easily. Ordinarily we recommend that exercisers avoid clothing made from nylon or rubberised fabrics that prevent evaporation of perspiration. Thus cotton clothing is considered as an excellent material for facilitating the evaporation of sweat.

Prolonged vigorous exercise in your sauna suit can be dangerous in hot, humid weather conditions because it prevents the evaporation of your sweat which would help to control your body temperature. The hotter your exercise environment gets the more water the body loses through sweat. Likewise, the more humid the conditions are, the less efficient the sweating mechanism is at lowering your body temperature.

If you lose too much water or if your body temperature rises too high you could suffer a heat disorder such as heat exhaustion or heat stroke. The problem could be further complicated by the fact that when the environment's temperature approaches the temperature of your body, heat loss through convection and radiation stops.

When the environmental temperature is above your body temperature, the only means for heat loss is via evaporation of sweat. Radiation and convection reverse their direction and add heat to the body. Sweating then is the only avenue for heat loss at temperatures above skin temperature.

Body heat

With the use of the sauna suit the mere process of sweating is not in itself the most effective way of dissipating heat or losing weight. Sweat must be converted to a gas by evaporation before any heat loss occurs. When the air surrounding your body is not only hot but also humid, evaporative cooling is impaired. Evaporation cannot take place unless air is available to take up the water vapour that is produced. When the air is saturated and the temperature is higher than the skin temperature no heat loss will occur. Consequently our body heat will build up and our body temperature could rise to dangerous levels.

In a hot, humid environment, exercise increases our stress and dehydration levels. This is aggravated by a decreased ability to unload water vapour into an atmosphere that is already humid. This makes it more stressful for us to cope with the demands of exercise. Our level of fatigue builds up when the rate of heat loss from the body is not sufficient to balance the body's rate of heat production.

Kenneth Gardner is an exercise physiologist at the G. C. Foster College of Physical Education: email: yourhealth@gleanerjm.com.