By Dr. Marni Wesner, Sport Medicine Consultant. Glen Sather Sport Medicine Clinic
During the dog-days of summer, our pursuits turn toward a variety of outdoor activities and fun in the sun. While we have our fun, we should pay attention to the potential perils of exercise in the sun and heat.
Generally, 70 to 80% of energy the body produces is heat. With strenuous activity, heat production can increase 15 to 20 times. This could mean an increase in core body temperature of 1°C every five minutes unless there is an efficient way to dissipate heat. As your body temperature rises, the ability to regulate temperature is affected and, if you’re not careful, this can result in significant medical issues and injury.
The human body regulates heat through four different mechanisms:
- Conduction, such as heat loss with wet clothing or contact with surfaces
- Convection, such as heat loss with wind chill
- Radiation, such as heat loss due to flow of heat from hot to cold objects
- Evaporation of sweat
In the heat, your body relies primarily on radiation and evaporative cooling. When you are active, your body temperature rises, causing blood vessels in the skin to dilate. This results in an increase in blood flowing to the skin and an increase in sweating. With the evaporation of the sweat, the skin is cooled, which cools the blood and the body.
If you don’t drink enough water (dehydration), your body may have problems regulating heat. Dehydration results in less volume of blood circulating in the body, which causes the blood vessels in the skin to constrict and directs blood away from the skin. This can cause a heat-related illness. Your body is well hydrated if you urinate at least four times a day, the urine is a very pale yellowish color and you do not feel thirsty.
Heat cramps are the result of dehydration. The body temperature increases, causing painful muscle cramps and spasms (sometimes referred to as a “Charlie-horse”). This happens primarily in the large muscle groups such as the calf and thigh, but can occur in any muscle, including the diaphragm. Heat cramps can be prevented by paying close attention to proper hydration when exercising in the heat. Water is the key to maintaining hydration and is more important than sport drinks full of sugar and electrolytes. Drinking plenty of water before and during exercise is important.
Treatment of heat cramps involves rehydration, rest, cooling the skin, application of pressure to muscle and gentle stretching. Low and progressive acclimatization to exercise in the heat helps prevent heat-related illnesses.
Heat syncope is a more serious form of heat illness associated with feeling weak, fatigued, dizzy or faint; a weak but rapid heart-rate; and heavy sweating. Heat syncope results from more advanced dehydration and occurs when the body fails to dissipate heat.
To treat heat syncope, stop all activity and remove the person from direct sunlight. Apply iced towels or other forms of direct cooling such as fans or a cool water bath. It’s very important to replace water loss with plenty of cool fluids/water.
If heat syncope is not recognized and treated, it can lead to a more serious medical condition called heat exhaustion.
A person with heat exhaustion may have a headache, tingling in arms/legs, extreme weakness, exhaustion, profuse sweating, normal or slightly elevated body temperature, thirst, decreased urination and giddiness. It can progress to unconsciousness.
Urgent treatment of heat exhaustion involves cooling the body, providing intravenous replacement fluids and electrolytes, and hospitalization if the person is unconscious or vomiting.
If untreated, heat exhaustion can lead to heat stroke, which is a life threatening emergency.
Heat stroke causes headaches; convulsions; loss of consciousness/coma; a rapid pulse; and very hot, dry, red skin because the body has lost the ability to sweat. When a person’s body temperature is greater than 40°C (normal is 37.5°C) the body loses its ability to regulate heat loss and a crisis is created.
Heat stroke requires urgent treatment—rapid cooling of the body with ice packs, iced towels and/or a cold water bath is vital. The person requires hospitalization and rapid fluid replacement, and must be closely monitored to ensure the heart and kidneys don’t fail.
The most important risk factor for heat-related illness is dehydration. Other risk factors for heat injury include:
- High temperature
- High humidity
- Increased sun (i.e., no cloud cover)
- Absence of wind
- Illness or injury
- Lack of acclimatization to exercise in the heat
- Sunburn (diminishes the ability to sweat)
- Excessive sun block (diminishes the ability to sweat)
- Excessive or tight clothing, dark clothing, rubberized clothing
- Low level of fitness
- Alcohol abuse
- Age (Under 15 years, over 40 years)
PREVENTION is better than treatment of heat injury:
- Avoid activity at the hottest time of day.
- Use shaded areas for activity whenever possible.
- Ensure adequate and continual fluid intake.
- Be aware of early signs of heat injury and respond appropriately
- Ensure appropriate level of fitness and acclimatization.
- Wear lightweight, loose fitting, light colored clothing.
This information is provided for your knowledge only and does not replace the medical advice of your personal physician. Talk to your doctor for more specific medical advice tailored for your health needs.