Kenneth Gardner

Dear: Mr. Gardner,

Your article, 'Work up a sweat', September 21, 2006, was very informative and indeed well written. I wish, however, for you to shed light on a few concerns in regard to the deliberate attempt by some individuals to induce sweating during exercise.

It is my opinion that some 'gym goers' are convinced that increased sweating is a clear indication that fat is being burnt. To facilitate this sweating process, I have seen persons exercising in full sweat suits and even plastic sauna suits in a misguided attempt to burn fat.

Scientific evidence suggests that such a practice is imprudent and even dangerous given that most people exercise in environments with the ambient temperatures averaging some 88 degrees (F).

In your article, you noted that sweating is indicative of an increase in the use of energy that results in weight loss. While there is some truth in this, the uninformed individual may construe this information as more sweat, more fat burned, while scientific evidence informs that such weight loss is predominantly water and has very little indication on actual fat burnt.

I would, therefore, be grateful for further insights into these concerns as they relate to health and fitness.

Sincerely,

John O.Campbell

Deputy Programme Manager

Sports Development

CARICOM Secretariat

Turkeyen, Greater Georgetown

Guyana

Response to John Campbell

When continuous or intermittent exercise is performed for a prolonged period of time, this can lead to increased sweating and a reduction in body water. If exercise is performed in a hot or humid environment, the potential for dehydration is increased. In addition, the heat that is generated by the exercise combining with the heat from the environment can also increase the risk of excessive body heat. This excess heat can cause the development of complications for our heart and brain and difficulties in performing our exercise.

Changes in our body temperature during exercise are influenced by the chemical activities in our body, the environmental temperature and our effectiveness in heat loss via evaporation. In many environmental heat stress conditions, the change in our body temperature is not influenced by the environment, but mostly due to exercise.

As the intensity of exercise increases, our body temperature rises. Our body temperature during exercise is influenced by the function of our heart and lungs and the degree of our acclimatisation to heat exposure.

The loss of large volumes of fluid from our body also has a detrimental effect on sweating. As our body loses more water, our sweat rate decreases and our body temperature increases. If our fluid loss becomes severe, our sweat response can dramatically decrease and increase our risk for heat injuries. Submaximal exercise performance is also impaired in a hot environment. Exhaustion occurs at a faster rate as well as at a lower body temperature when we are dehydrated during exercise in a hot environment.

Given the devastating results of dehydration to exercise tolerance, fluid ingestion during exercise is vital to decrease the rate of exercise-induced dehydration. Our body can acclimatise to hot or humid environments or be acclimated to tolerate exercise in such conditions.

When sweating occurs naturally as a result of our body's response to the exercise being done, some energy would have been utilised during the process. However, sweating can also occur because of how we manipulate the changes in our body temperature as you mentioned with plastic sauna suits. This would certainly not be due to the use of fats by our body.

During prolonged exercise, we use energy from a variety of areas to carry out the routine. The relative priority of these energy sources changes for different intensities and duration of the exercise. During low intensity, endurance exercise fats predominate as the primary source of energy. On the other hand, the reliance on carbohydrates increases as the exercise intensity increases. When the body's stores of carbohydrates are low, there is an increased use of fats and protein as the source of energy. The longer we are able to maintain our exercise at a submaximal level, the greater are our chances of using fats as a fuel.

However, soliciting increased sweating artificially, that is, without physical work or increasing the environmental temperature, will result in water loss and certainly not at the expense of fat.

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