During exercise, the body increases its metabolism to provide energy for muscles. With intense exercise, this increase can be 15 to 20 times the resting metabolic rate. That means there is a lot of heat produced! Sweat production with evaporation is one major mechanism the body uses to get rid of this heat.

Temperature regulation in the body depends on extrinsic (environmental) and intrinsic (personal) factors. These factors, especially if several exist together, can lead to illness or injury, perhaps severe.

Environmental factors:

Atmospheric temperature:

Humidity - in very humid conditions, body sweat can’t evaporate as easily
Location - beach or open water, no shade
Duration and intensity of exercise - longer, more intense activity produces more body heat

Personal factors

Personal health:

Age - children perspire less than adults and have a lower heat tolerance
Fitness - less fit people and obese individuals are more at risk for heat-related problems
Recent illness or injury
Inadequate hydration
History of previous heat-related illness

What is heat-related illness?

When the body’s heat production is greater than its ability to get rid of heat, a variety of problems occur. These range from mild and unpleasant to life-threatening. If you are exercising in the heat, watch for the following signs and symptoms:

Feeling very hot, thirsty, nauseated, dizzy or having headache or pounding heartbeat
Excessive sweating or perhaps no sweating
Fatigue, muscle heaviness or tightness
Clumsiness, irritability or loss of judgment (brain signs).

Types of heat-related illness

Heat cramps, muscle spasms - often in the calves or abdomen. In these cases, the body’s core temperature is normal but the individual may have lost significant body water and sodium through sweating. Treatment: If you get heat cramps, rest in a cool place and drink water or diluted sports drinks. Gentle calf stretching may be done.
Heat syncope (faintness) - This may happen when a dehydrated person stops exercising. Blood in dilated vessels drops to the legs, and feelings of lightheadedness suddenly occur. Prevention and Treatment: To avoid this, drink adequate water before and during exercise. Walk to cool down after vigorous activity. If you feel faint, lie down in a cool place, with your legs elevated and drink water.
Heat exhaustion - This is the result of even greater loss of body water. This person is very dehydrated, hot, and extremely weak and exhausted. There will be profuse sweating, a rapid heart rate and an altered mental state (confusion, giddiness, uncharacteristic irritability, maybe even delirium). There may be headache, muscle cramps, vomiting or diarrhea. This individual is very ill! Treatment: Begin with rest, cooling (fan, cool packs to the neck, underarms, groin) and offering water, if the person can drink. A person with signs of heat exhaustion should be taken to a medical facility for further evaluation and care.
Heat stroke - This is a medical emergency! The body’s heat regulation has failed. The skin is hot and dry. The nervous system is impaired; disorientation, agitation, delirium and coma are possible.

Consequences of heat stroke may include heart attack, kidney failure, brain damage or death. Treatment: Rapid external cooling should be started, but emergency transport to a hospital is essential. Heat exhaustion and heat stroke can appear very similar. Thus, any symptoms of either condition when a person has been exercising in the heat should make observers act quickly.

Heat-related illnesses can be avoided. It is important to understand risks involved. Exercise with care and good sense if any of them exist. It is best to exercise with other people, rather than alone. If you notice signs of heat-related illness in someone, tell that person, as the early warnings may not be obvious to the person. Slowing the pace of exercise, drinking extra water and cooling are all helpful suggestions.

Solar Injury

Solar injury is the damage done by sunlight to skin and eyes. It can happen immediately after exposure to the sun or maybe years later. The damage is potentially very serious.

People who exercise in the heat should take precautions about sun exposure. Fair-skinned individuals or those with previous sun-related skin damage (history of bad sunburns, “sunspots” or skin cancers) are more at risk. The very young and the very old are also more vulnerable to solar injury.

Sunburns vary from mild to severe. The chance that you will be sunburned depends on the sun intensity, the reflected or added UV radiation (water, snow, even pavement), your skin type and how long you are out in the sun. Remember, up to 80 per cent of UV radiation penetrates cloud cover and up to 50 per cent reaches swimmers through water.

Sunburns carry possible long-term health risks. The sweat duct lining cells are easily damaged by UV light. Once damaged, the ducts can become blocked, thus decreasing the ability to sweat. This can lead to higher risk of heat-related illness.

Sun exposure repeatedly over time is linked to skin cancers such as basal cell and squamous cell cancers. Blistering or short, intense sun exposure is associated with melanoma skin cancer. More rapid aging and wrinkling of skin occurs in people who have higher sun exposure. Most of the sun-related skin changes, from aging to cancers, are irreversible.

The eyes are particularly vulnerable to sun exposure. Immediate problems may include pain, tearing, redness and swelling of the eye surfaces (keratoconjunctivitis, corneal damage). This can be very painful and result in decreased vision. Long-term eye damages related to sun exposure are cataract formation and retinal degeneration.

Children - Special Heat Considerations

Children are not small adults. When they exercise in the heat, they have special risks because of unique physical and psychological characteristics. For every kilogram of body weight, children produce more heat during exercise than adults. Also, they do not sweat as much as adults.

Rather than sweating as the major means of heat loss, children rely more on convection (heat from a hot body dissipating to the cooler surrounding air). When the outside temperature is higher than skin temperature, this system fails. Children have less heat tolerance than adults. For a given level of dehydration, children have a greater increase in core temperature than do adults. When these facts are added to other risks such as dehydration, obesity or poor conditioning, certain children may become quite ill while exercising in the heat. Since children are shorter than adults, their bodies are closer to reflected solar energy from sand, water and pavement. Thus they are more prone to solar injury. In addition, children’s skin is ‘thinner’ and more vulnerable to sun damage.

Excessive sun exposure and frequent sunburn in childhood (under 18 years of age) are associated with higher risk of skin cancer in later life.

When children play or compete, they are likely to overlook good health practices. They forget to drink water before, during and after exercise. Seeking shade, cooling down, wearing protective clothing and hats and applying sunscreen also may be forgotten. Children may not feel the effects of heat as early as adults and they often recover quickly to ‘jump right back into the heat.’ This can lead to careless attitudes about safety for exercise in the heat. If children become ill, or have an injury, they become more vulnerable to heat-related illness in their usual sports activities. Parents and coaches should encourage and remind children to follow basic rules for safety in the heat all the time!

Prevention of Heat-Related Illness and Solar Injury

Prevention is simple. You need only to make smart decisions about what to drink, what to wear and what to watch for.

Hydration - what to drink

It is important to drink before, during and after exercise in the heat. This means extra water added to your usual intake. The more you sweat (depending on weather, exercise intensity and duration and fitness) the more water you should drink. Water is good fluid replacement for exercise lasting one hour or less. It is more quickly absorbed than sports drinks. Cool water is better absorbed than hot fluids.

Guidelines for amount of water to drink:

Before exercise - 2 cups, 2 hours before and 1 to 2 cups, 10 to 15 minutes before
During exercise - 1/3 to 1 cup every 15 to 20 minutes of sustained, intense exercise
After exercise - 2 cups for each half kilogram of weight lost during exercise or drink water until the urine is clear.

Remember - thirst is not a good guide about dehydration or adequate fluid replacement. Caffeine and alcohol have a diuretic action, thus increasing the body’s loss of water. A cold beer on a hot day will not help your hydration!

What to wear

Clothing - light-coloured, lightweight, porous fabrics are best. Males should wear a shirt for protection from solar injury. Malignant melanomas are common on the back.
Hat - a light-coloured hat will reflect heat from the head. Baseball caps are not enough. Hat brims should be three inches wide all around.

Sunscreen - there are two categories of sunscreen:

Chemical sunscreens absorb ultraviolet radiation. Examples are PABA (paraaminobenzoic acid esters), salicylates and cinnamates.
Physical sunscreens scatter or reflect ultraviolet radiation. Examples are zinc oxide and titanium dioxide.

Choose a sunscreen with SPF (sun protection factor) of at least 15. SPF 30 sunscreen is much better than SPF 15 to prevent early DNA damage to skin cells - related to possible cancer. Also higher SPF values compensate for sweating or loss of sunscreen in water. Use about one ounce of sunscreen for wholebody coverage. Remember to apply around your eyes, ears and mouth. If you are bald or have thinning scalp hair, also apply sunscreen on the scalp.

Reapply sunscreen hourly if you are swimming and often during exercise if you are sweating. Water-resistant sunscreens should be reapplied after 40 minutes of water exposure or with sweating. Water-proof sunscreens need reapplication after 80 minutes.

Sunglasses - choose glasses that offer good protection from ultraviolet radiation. ‘Special Purpose’ glasses give the most protection. UV radiation, especially UVB, is a risk factor for the development of cataracts, keratitis and corneal problems. ‘Special Purpose’ glasses block at least 99 per cent of UVB. ‘General Purpose’ glasses block 95 per cent of UVB radiation. For sports activities, choose lenses of polycarbonate or lexcan, which will not shatter.

What to watch for

Exercise during cooler times of the day to avoid the midday sun. UV light is five times greater during midday than at other times. Remember factors that may alone or in combination increase the risk of heat-related illness or solar injury. Being unacclimatized (not used to the temperature, humidity and altitude of a place) will increase risk. Children need special attention. Exercising when you are ill, overtired or injured is not wise - the body’s temperature regulation, endurance and strength may be abnormal.
Someone who has had any heat-related illness (heat cramps, exhaustion or heat stroke) would be wise to recognize their vulnerability and their increased risk of another occurrence of heat-related illness. The same applies for solar injury - sunburn or sun-related eye damage. Think of these things and plan for safety.

Exercise in the heat can be fun and beneficial for health and fitness. It can also be safe if done properly. It is important to drink lots of water, wear appropriate hat and clothing, use sunscreen and sunglasses and be aware of the warning signs of heat-related illness.

Exercising in the Heat Stay fit while avoiding heat-related illness

What’s risky about exercise in the heat?