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Heat Injuries in Mountain Bikers

By Brian Fukushima, MD
NMBP Medical Advisor

Scenario:

You are riding on a difficult, exposed trail with a significant elevation gain. It is the middle of the afternoon on a muggy summer day. You come across two riders panting by the side of the trail. One of the riders complains of nausea, dizziness, and fatigue. On examination, he is breathing rapidly but without difficulty, his heart rate is rapid, and his skin feels very warm. He says he feels ok, but just needed to stop for a short rest.

What is your diagnois and what do you do next?

Introduction:

Heat related illnesses can be common injuries especially among athletes engaged in strenuous activities of long duration. Heat injuries are usually the result of a combination of factors including:

 

  • Increased environmental temperature and humidity: Ever try riding Utah's White Rim Trail in the middle of summer, or hiking the Kalalau Trail on Kauai during the middle of the day? Direct exposure to sunlight, heat, or humidity can increase the body's temperature.
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  • Increased heat production: Intense physical activity can increase the body's production of heat. Strenuous exercise can increase the body's temperature 1 degree every 5 minutes (if heat production cannot be dissipated).
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  • Decreased heat dispersion: The body may lose its ability to effectively get rid of excess heat. This is usually the result of dehydration. Another important factor is clothing choice. Most high-quality cycling apparel is designed to maximize wicking and aid in heat dispersion, but novice riders will often choose heavier cotton or other non-wicking materials that impede the body's efforts to shed heat.

A sampling of heat injuries

There are two main types of heat injuries, ranging from mild heat exhaustion to life-threatening heat stroke.

Heat Exhaustion

This common condition is usually the result of salt and water (volume) depletion. The body's temperature is usually within a range from normal (98 degrees) to 104 degrees Farenheit.

Symptoms include:

 

  1. dizziness
  2. fatigue
  3. weakness
  4. lightheadedness
  5. nausea
  6. vomiting
  7. headache
  8. muscle ache

When you examine a rider suffering from heat exhaustion you may find:

 

  1. rapid heart rate
  2. rapid breathing
  3. excessive sweating
  4. increased body temperature
  5. fainting or lighheadedness when standing from decreased blood pressure

Treatment:

 

  1. Rest. Remove the cyclist from direct heat or sun exposure into shade or shelter.
  2. Remove excessive clothing.
  3. Use cool compresses or ice directly on the skin.
  4. Provide fluid to the injured cyclist. Water is acceptable but sports drinks contain fluid plus electrolytes. Additionally, since sports drinks are flavored or sweetened the cyclist may be willing to drink more.

As outdoor athletes, many of us have suffered from the symptoms of heat exhaustion. These symptoms usually respond to rest, cooling, and hydration. While not severe, if untreated the symptoms can escalate into a serious condition known as heat stroke.

Heat Stroke

Heat stroke occurs when the body is no longer able to effectively cool itself and begins to shut down. It should be treated as a medial emergency with immediate evacuation and treatment in a hospital setting.

A patient with heat stroke will have a temperature above 105 degrees Farenheit, nervous system degradation, and a lack of sweat production.

Symptoms may include:

 

  1. All the signs and symptoms of heat exhaustion
  2. irritability
  3. bizarre behavior
  4. confusion
  5. hallucinations
  6. clumsiness

These symptoms demonstrate involvement of the central nervous system (brain and spinal cord). Many of us ride with friends with these symptoms (usually brought on by a certain beverage) but in the setting of heat and sun exposure, suspect heat stroke.

Other signs of heat stroke may include:

 

  1. Excessive body temperature
  2. Dry skin and lack of ability to sweat
  3. Abnormal body posturing
  4. Excessive weakness
  5. Shock
  6. Seizure
  7. Coma

Treatment

Cool down the body temperature!

The immediate (field) treatment for heat stoke is rapid cooling to below 104 degrees Farenheit. Ice packs placed in the armpit and groin and cool, moist compresses will help decrease the cyclist's temperature. Fanning the patient or encouraging the flow of air over the cyclist's body will also help decrease the patient's temperature. Also remember the ABC's of first aid (airway, breathing, circulation) especially when dealing with a patient with nervous system problems. Finally, evacuation to the hospital for more specialized treatment is essential.

Conclusion

Heat stroke is much more severe than heat exhaustion. It is a life-threatening emergency. Heat exhaustion is far more common on the trail and can vary in severity from a minor distraction to debilitating weakness. Usually heat illnesses can be prevented with proper hydration, clothing, preparedness and knowledge of conditions.

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