dehydration and heat injury
PAPA DOC, WINDY CITY ROLLERS
“No sweat” means “it’s good,” right? Not the case, when exercising in hot, humid weather, when it means danger. Sweating may be a social problem, but it is a life saving process for you on the track.
The core temperature of your body is maintained in a narrow range (about 97°–100°) in a wide variety of environments. This is necessary because at too low a temperature, bodily functions slow down and cease. At too high a temperature, the body essentially cooks.
The body gains heat from several sources. The major contribution is from metabolism and muscle activity: under most conditions, about 70–90% of total heat production. Radiation from hotter objects in the environment – such as the sun and hot pavement – is variable. High air temperature adds heat, especially with high humidity and no air movement.
Achieving heat loss involves two sets of activities: behavioral and physiological.
The behavioral responses are:
- Altering the amount of muscle activity
- Reducing clothing
- Quenching thirst
- Seeking shade
The physiological processes are:
- Conduction to colder objects (usually a small loss)
- Convection which is dependent on air movement and an air temperature lower than the skin temperature (90°–92°)
- Radiation heat loss dependent on clothing and on the heat of surrounding objects
- Evaporation (usually the major means of heat loss when the air temperature is the same or higher than the skin temperature)
Sweating accounts for the main evaporative loss of heat; respiration contributes a small amount. The ability to lose heat by sweating depends on the ability to sweat efficiently both in volume and in the water content of the sweat, the delivery of blood flow to the skin (i.e. circulation must be adequate), the sweat actually evaporating (limited in humidity > 60%), air movement and clothing and equipment (the extent of body covered and the type – e.g. non-breathing fabric).
Your ability to lose heat is reduced by poor physical conditioning, high body fat, certain medications, inadequate hydration, alcohol and caffeine, sunburn (reduces the ability to sweat), fever, clothing and equipment, and lack of acclimatization.
types of heat injury
When heat loss is impaired, the body suffers heat stress and eventually actual injury in one of several forms: heat cramps, heat exhaustion or heat syncope and heat stroke. Heat cramps are the mildest form of injury. More severe is heat exhaustion or heat syncope. Heat stroke, when the body’s heat loss functions fail, is the most dangerous. Heat stroke can be fatal. Although the milder forms may warn of impending heat stroke, heat stroke may occur without the less severe stages. Therefore, you must be alert to the warning signs and symptoms.
Heat cramps are just that: cramps in the limbs and/or abdomen. If there are cramps all over the body, this is a more serious symptom.
Heat exhaustion and syncope occur when the body is still coping with the excess heat, but is under major stress. The symptoms are weakness, exhaustion, dizziness, confusion, fainting, excessive thirst, cool sweaty skin, cramps, headache, and chills. The pulse will be rapid. The blood pressure will be normal to low. The body temperature is up to 104°. The confusion can interfere with the behavioral activities to reduce heat. Therefore, it is imperative for teammates to watch out for each other.
Heat stroke is a true medical emergency. The body’s protective functions have failed. The symptoms of weakness, dizziness, confusion, headache and/or fainting are present, but the skin is now dry and hot. Nausea and vomiting occurs. Collapse with coma and seizures may occur. The pulse is very rapid and weak. The blood pressure is low. The body temperature is 104° or higher. Death is a distinct possibility when the body temperature is over 107°.
treatment of heat injury
Heat cramps are treated by moving the skater to a cool, shaded environment with cooling measures such as fans or cold wet towels. Removing clothing, stretching the cramped muscles and providing cool electrolyte-containing fluids should relieve the cramps. Your medical team must evaluate the skater.
When you are dealing with heat exhaustion or syncope, cooling measures (fans, cold towels and ice packs) are essential as are electrolyte-containing fluids (if the skater is alert enough to swallow). Medical evaluation and treatment are required.
Heat stroke is an absolute medical emergency. Call 911 while moving the skater to a cool, shaded environment. Immediately begin cooling with fans and ice packs (if available, provide an ice bath) until the emergency medical help arrives. The skater will not likely be able to take oral fluids and will need intravenous (IV) fluids.
prevention of heat injury and dehydration
Acclimatization is conditioning the body to cope efficiently with heat, achieved by slowly increasing the amount of activity in a given climate over one to two weeks. This improves sweating capacity to allow more efficient evaporative cooling with less mineral loss. Acclimatization will reduce the body’s core temperature, improve the thirst response, and increase blood flow to the skin as well as improve the capacity of the heart to respond to the increased demands. You can lose acclimatization “progress” if you are inactive for more than a few days.
Environmental factors can be controlled by reducing or changing clothing, getting to a cooler or shadier area, reducing the physical activity and by reducing the ambient temperature and humidity with fans and air conditioning.
Maintaining adequate hydration is critical, not only for coping with heat, but for physical performance in general. Pre- hydration is a must: drinking 24 oz of fluids two hours before and another 8 oz right before exercise. The type of fluid is important and should be non-caffeinated, non-alcoholic fluids that supply water and electrolytes. Water is the best choice for the first hour or two of exercise. After that, electrolyte- containing, low sugar fluids such as non-caffeinated sports drinks and coconut water are good. During moderate to heavy exercise, about 3/4 to one quart of fluids per hour (usually 8 oz every 20 minutes) is needed in temperatures over 78°. Breaks for water also allow for moving to cooler areas.
The most important electrolytes to supply are sodium (salt) and potassium. Salt is obtained through salting foods and eating salty foods when exercising. When not exercising regularly, a lower salt diet is better. Salt tablets are not recommended. Potassium is ingested through a variety of foods: vegetables, nuts and fruits (especially bananas, cantaloupes, tomatoes and coconut water). Sports drinks should have 15–30 meq/liter of sodium and 2–5 meq/liter of potassium. Lower sugar concentrations (5–10%) are advised, because of weight gain concerns and because higher levels of sugar can induce diarrhea. The maximum daily fluid intake should be no more than 12 quarts.
You can “measure” your level of hydration in two simple ways. First, your urine should be clear to pale yellow. Second, weigh yourself before and after exercise. With adequate fluid intake, you should not lose more than 2% of body weight. You should replace any weight loss by drinking about 24 oz of water for each pound lost.
Other factors in body heat maintenance can be controlled. Improving general physical conditioning will reduce your level of body fat as well. Check with your doctor about any and all medicines you take (both OTC and prescription) and their effects on heat tolerance. Avoid alcohol and caffeine before exercise. Don’t exercise if you have a fever. Avoid sunburn – this also protects against skin cancer. If you are ill, reduce or avoid exercise until you are well. Wear the minimum clothing needed and use moisture-wicking and breathable fabrics.
Sweating can save your life, so “bathe” in it. Wearing deodorant and washing your pads is still OK.
- from fiveonfive #8, Summer 2010