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Heat Alert! Exercise and Hyperthermia

Posted on 29 April 2015
Heat Alert! Exercise and Hyperthermia

As the summer moves on, many of us continue to enjoy the blue skies and warm temperatures. Whether its jogging, rollerblading, cycling, golfing, or just going for a walk, exercising in hot climate can do more than make us hot, exhausted and thirsty. Exercising in warm weather is safe if you know how to manage your exercise program and adjust your workout to the conditions. This article discusses the concept of hyperthermia as it relates to exercise, lists some key features of the various heat stress related disorders, and provides some tips for prevention of heat related injuries.

While exercising you are exposed to both external and internal heat. External heat comes from the combination of environmental temperature and humidity. Humidity increases the effect of heat by limiting the effectiveness of sweat evaporation to cool you. Heat radiation from certain surfaces such as pavement, concrete or sand may make you feel hotter. During intense exercise, muscle activity increases internal heat production 15 to 20 times more than at resting levels. Exercise intensity and duration, body size and shape, fitness level, acclimatization, state of hydration and type and color of clothing also affect internal heat production.

The body is always attempting to maintain a constant internal temperature of approximately 37°C. Once this balance is disrupted, the body will activate various mechanisms to achieve temperature balance. As the brain senses a rise in body temperature, the immediate response is vasodilation (opening) of cutaneous (skin) vessels, which increases blood blow to the skin where heat can be dissipated. When blood flow is directed more to the skin, less blood becomes available to flow towards the visceral organs. This pooling of blood in the extremities may lead to symptoms of headache, dizziness and exhaustion. If external temperature exceeds the body's internal temperature, the ability to lose heat is diminished, and heat must be lost by evaporation of sweat.

Severity of heat illness progresses as described below; from the mild stages of heat cramps and heat fatigue through more serious heat exhaustion, heat stroke and hyponatremia. The latter two conditions can be fatal.

Heat Cramps:  Painful spasms of muscles caused by electrolyte imbalances and dehydration secondary to sweating.

Heat Fatigue:  Symptoms include weakness, dizziness and headache, accompanied by signs of dehydration such as rapid weak pulse and lowered blood pressure. To recover from this stage of heat illness, stop your activity; get to a cool place, apply ice packs to your groin and armpits, and aggresively replace fluids with a balanced electrolyte solution.

Heat Exhaustion: Worsening symptoms of weakness, dizziness, mental confusion and dehydration. Sweating continues but is accompanied by an elevation of body temperature. Dehydration has impaired the body's ability to regulate heat, and body temperature rises to as much as 40°C. Hospitalization and intravenous fluids may be required. Aggressive cooling measures are also needed.

Hyponatremia:  This condition arises from inadequate replacement of sodium, an important electrolyte lost in sweat. Symptoms of hyponatremia include muscle cramps, nausea, headache, dizziness, exhaustion, stomach upset, delirium and coma. Some cases of hyponatremia are fatal. Treatment may include administration of high sodium containing fluids, and hospitalization is required in certain cases.

Heat Stroke:  The body loses its ability to sweat due to profound dehydration, and body temperature continues to rise, above 40°C in some cases. Symptoms include hot dry/red skin, disorientation, and strong rapid pulse. Immediate cooling and hospitalization are required.

If you encounter symptoms of hyperthermia, stop exercising, drink something cool, relocate yourself to a cooler/shaded area, put cool compresses on your armpits and groin and loosen your clothing.


Steve Wong  BHK, BSc PT, MCPA
Physiotherapist  Printed: September 2002
Copyright ©2002 SEMI

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