Sun sport safety - exercising in the heat

Sun Sport Safety

As summer approaches, even the most dedicated fitness enthusiasts start thinking of ways to avoid exercising in the heat. For most individuals, performing physical activity in the heat requires a great deal of effort, and performance is generally less than ideal. Overexposure to the heat while exercising not only results in decreased work performance, but also a predisposition to serious heat illness. By adequately preparing for the summer months, athletes can avoid most of the discomforts associated with exercising in the heat and prevent serious heat illness. Following are some basic guidelines and training considerations when exercising in the heat.

A basic understanding of environmental physiology, including heat balance, temperature regulation, physiological changes due to heat training and heat disorders is essential to understanding how to survive when exercising in the heat. Human beings are able to live, work and exercise relatively independent of the environment because of their ability to maintain constant body temperatures. However, because we are homeotherms - meaning internal temperatures must be regulated - a large variance from the normal resting body temperature of 37 degrees celsius can be catastrophic. Heat must be removed from the body or body temperature will climb and cause overheating.

Humans regulate body temperature through a process known as thermal balance - the regulation of the production of heat and the loss of heat. The human body gains or loses heat as a result of four heat exchange processes - convection, conduction, radiation and evaporation. Of the four processes, the greatest amount of heat loss occurs through evaporation which takes place through sweating. Profuse sweating is the most effective means of losing heat and cooling the body. However, cooling only takes place when sweat evaporates from the skin.

Evaporation is greatly affected by the relative humidity. Relative humidity is the amount of water vapor in the air, relative to the amount of air it can hold. As the relative humidity increases, heat loss through evaporation decreases. When sweat drips off the body during or following exercise, it probably means the temperature is low, but humidity is high and evaporation cooling is not taking place. Under these conditions it may be difficult to regulate body temperature since most heat illnesses occur during this time.

Four environmental factors determine the ability to lose heat, they are wind speed, humidity, temperature of the air and the amount of radiant heat. Loss of heat is increased by circulating air. Exercising in cool wind or during a slight breeze will help facilitate cooling. Heat is also lost through radiation, when our bodies temperature is warmer than the surrounding environment. Thus, running in the shade is better than running in the direct sunlight. If possible, exercise session should take place during the coolest period of the day.

The best way to avoid serious heat injuries is to prepare in advance of changing environmental conditions. Allowing the body to gradually acclimatize to the heat will improve the circulatory and sweating responses, which facilitate heat dissipation. Acclimatization is accomplished by a progressive exercise program performed in the heat for one to two weeks. Another important benefit of acclimatization is a lowered skin temperature during exercise, which means less blood flow is required to transfer excess heat enhancing performance. Some of the changes that occur with heat acclimatization include decreased heart rate, body temperature and salt loss in sweat, whereas sweat rate and the on-set of sweating increase.

For most individuals, exercising in the heat may be uncomfortable, but generally tolerable. For some however, exercising in the heat becomes intolerable, and even life threatening. Poorly conditioned, non-acclimatized and obese people have the most difficulty versus those people who live, work and exercise in hot and humid conditions. Severe thermal distress is commonly seen in endurance events, football and in highly competitive events. These types of athletic events should be well monitored, and supervised by competent individuals familiar with the treatment of thermal illness, and with the precautions that should be taken when severe environmental conditions exist.

Anyone who exercises in the heat should be familiar with four symptoms of overexposure to the heat. Heat illness can be prevented, through proper conditioning, gradual acclimatization, and adequate fluid replacement. Athletes need to think ahead, and plan for special precautions when exercising in the heat.

A. Dehydration. In an attempt to counterbalance overheating, the human body increases sweat rates. Sweat is over 99% water, thus, prolonged sweating may cause dehydration. Dehydration in excess of five percent of total body weight limits sweating and circulatory capacity, and exposes athletes to severe health hazards.

The best prevention against dehydration is adequate fluid replacement before, during and after exercise. Fluid requirements usually never keep pace with body requirements and sweat losses. However, as long as water consumption equals sweat loss, dehydration can be prevented. Athletes that train frequently in the heat should keep a record of their weight. An athlete that loses two to three percent of their total body weight after a workout should not exercise again until adequate rehydration takes place.

B. Heat Cramps. Heat cramps are characterized by painful spasms of the muscles following hard work in the heat, usually caused by inadequate fluid replacement. The most common treatment for heat cramps is to move to a cool environment and drink cold liquids. Drinking plenty of fluids prior to, during and after exercise should help prevent heat cramps.

C. Heat Exhaustion. Heat exhaustion is characterized by weakness, dizziness, nausea, profuse sweating, headaches and eventually collapse. Have the person lie down in a shaded area and administer fluids when symptoms of heat exhaustion are present.

D. Heat Stroke. Heat stroke is a life-threatening reaction to heat exposure. It is characterized by a high body temperature, usually above 40.6 degrees celsius, cessation of sweating, rapid pulse and respiratory rate and usually elevated blood pressure. Anyone suspected of suffering from heat stroke should be taken to emergency facilities immediately.

The chances of developing heat illness can be reduced and/or prevented through adequate water and electrolyte replacement, acclimatization to the heat and awareness of the limitations by the combination of exercise, proper clothing and the environment. Fluids should be consumed in frequent intervals during exercise, even when not thirsty.

The Ideal fluid therapy when exercising in the heat includes:

1. A fluid with no more than 2.5g of glucose per 100ml of water. 2. No more than .2g of sodium per 100ml water. 3. Fluids ingested in frequent intervals and in volumes of 100 to 2001. 4. Fluids should be cold - four degrees Celsius.

Numerous studies have reported that the best fluid for rapid rehydration is cold water. Fluids that contain large amounts of sugar, or are warm, slow gastric emptying. And since water is absorbed in the small intestines, and not the stomach, anything that delays gastric emptying also delays rehydration.

Other suggestions for preventing thermal

distress include:

* Splashing water on the skin. * Planning for regular water breaks

during an exercise session. * Scheduling exercise sessions during

the cooler times of the day. * Avoiding the use of salt tablets. * Drinking plenty of water prior to

exercising in the heat. * Avoiding high intensity training on

days with no cloud cover and high

humidity. * Drinking a fluid that is cold (eight to

13 degrees Celsius), low in sugar (2.5

g/dl), with little or no electrolytes. * Being well conditioned prior to

exercising in the heat.

Adequate fluid replacement is an important factor in preventing heat illness, but is only one of many. Athletes should prepare for the summer months by gradually acclimatizing to the heat. Athletes that exercise frequently in the heat should be well educated on the different types of heat illness, and their treatments. People can tolerate extremely hot climates because of a well-developed ability to control body temperature. There are limits however, to the ability to regulate temperature, and each athlete must find that delicate balance between adapting to exercising in the heat and overexposure to the heat.

COPYRIGHT 1990 Aerobics and Fitness Association of America
COPYRIGHT 2004 Gale Group