Blog post from our board member Dr. Stephen Black, M.Ed., P.T., A.T.C./L., C.P.T. : TAKING THE HEAT: Hydration, Heat and Exercise.
By understanding the causes and symptoms of dehydration, you can help your clients to ensure they remain adequately hydrated in all situations.
Modern life is like a marathon: It includes sustained activity punctuated with opportunities to drink water. Unfortunately, many people tend to forego those opportunities, and a lot of people walk around in a state of mild dehydration. For example, after taking a two-hour plane flight, drinking a cup of coffee and heading to a meeting in an airtight office building, people can lose as much as 1 percent of their body weight. This fluid loss is significant enough to affect the body’s internal thermostat. Also, a 1 percent loss of fluid can increase the heart rate an average of 5 beats per minute.
You can help your clients and members stay healthy and hydrated by encouraging them to drink plenty of fluids, and by educating them about the dangers of dehydration and exercising in the heat.
Dangers of dehydration
Dehydration is one of the most common heat diseases, and few people go through life without being dehydrated at some time or another. It might be dismissed as a minor irritation, but dehydration is indeed something that deserves full attention and warrants timely treatment.
Dehydration can be defined as the loss of water and essential body salts (electrolytes) that are needed for normal body functioning. Lack of adequate fluids can hinder the body from carrying on normal functions at an optimum level. Water makes up about 60 percent of a man’s weight and 50 percent of a woman’s weight. This proportion has to be kept within a narrow limit to attain a proper balance in the cells and body tissue.
Water is the most important nutrient in the body. It makes up 70 percent of muscles and 75 percent of the brain. Oxygen is the only thing the body craves more than water. Through daily exhalation, an average of 2 cups of fluid are lost per day. Also, water evaporates invisibly from the surface of the skin at an average rate of 2 cups per day. Through urination, 2 pints are lost per day. During the course of a regular day, a healthy adult can lose 8 to 10 cups of water, not accounting for the loss that occurs with any type of physical activity.
After a failure to replenish these losses, a physiological chain reaction is initiated. Reading a “water shortage” message, hormones tell the kidneys to conserve water by urinating less, and the urine passed is amber-colored (healthy water intake produces light-tinted urine). Along with contributing to constipation and bloating, dehydration trips up the body’s systems. At a 3 percent loss of body weight, muscular endurance diminishes. At 4 percent, dizziness occurs and physical labor capacity declines by as much as 30 percent. At 5 percent, problems with concentration, drowsiness, impatience and headache occur. At 6 percent, the heart is racing and the body’s temperature regulation system starts to fail (athletes will notice that they stop sweating). At 7 percent, there is a significant chance of collapse. Moderate dehydration is said to set in when there is up to a 10 percent loss of body fluid. This is of great concern and immediate steps should be taken to rehydrate. Severe dehydration is said to set in when there is up to a 15 percent loss of body fluid. This should be treated as a medical emergency and might even require hospitalization to bring about normal electrolyte balance.
Causes
One of the main causes of dehydration is overexposure to high temperatures and/or the sun. This holds true for anyone who spends time in places of high temperature and relative humidity. Health clubs are a prime target for the development of dehydration and associated maladies. Dehydration is basically caused when the body loses water content and essential body salts such as sodium, potassium, calcium bicarbonate, and phosphate.
Adults older than 60 who drink only when they are thirsty probably get only about 90 percent of the fluid they need. (People older than 60 are especially susceptible to dehydration.) Developing a habit of drinking only in response to the body’s thirst raises an older person’s risk of becoming dehydrated. Dehydration in children usually results from losing large amounts of fluid and not drinking enough water to replace the loss. An infant can become dehydrated only hours after becoming ill. Keep this in mind if your facility offers childcare, preschool, etc.
Apart from overexposure to sun, high heat, and humidity, dehydration might also be caused by persistent vomiting, diarrhea, high fever, drugs (mainly from diuretics, which cause depletion of body fluids and electrolytes), alcohol and caffeine use, appetite loss associated with acute illness, excessive urination (polyuria), bacterial or viral infection or inflammation, and other causes, such as diseases.
Symptoms
Symptoms of dehydration at any age include cracked lips, dry or sticky mouth, lethargy and sunken eyes. A person who is dehydrated cries without shedding tears and does not urinate very often. The skin is less elastic than it should be, and is slow to return to its normal position after being pinched. An infant who does not wet a diaper in an eight-hour period is dehydrated.
Dehydration can cause confusion, constipation, discomfort, drowsiness, fever and thirst. The skin turns pale and cold, and the mucous membranes lining the mouth and nose lose their natural moisture. The pulse sometimes races and breathing becomes rapid. Blood pressure will decrease with dehydration. Significant fluid loss can cause serious neurological problems and hypovolemic shock.
Prevention
To prevent dehydration, make sure your clients and members start drinking water early in the day, and then drink it often. Make sure they drink plenty of fluids, especially when the environment dictates (during periods of high heat, humidity, excessive sun, etc.). The typical recommendation is to drink six to eight 10-ounce glasses of water a day, but determining water intake is not an exact science.
Advise your members to keep bottled water on hand in containers that fit into the bottle holders on the equipment at your facility. Make sure water fountains function appropriately (adequate flow) and are cleaned regularly. Recommend drinking regularly at work, home and the gym. Tell your clients to think of drinking as akin to breathing, and water as the purest, most replenishing oxygenated air — a critical element of life.
For your members to find out how much fluid they lost during exercise, they can weigh themselves nude and dry prior to exercise, and nude and dry after activity. For every 1 pound of fluid lost, 1 pint of fluid must be replaced. Have them drink 4 to 8 ounces every 15 to 20 minutes during exercise, in addition to at least 8 ounces before exercise. For exercise lasting less than 20 minutes, water is the best fluid replacement.
Rehydration begins with water, possibly a salt-water solution, and/or a commercial sports drinks for maintaining or returning electrolyte balance. An alternative method is gelatin water for electrolyte replacement, made by diluting a 3-ounce package of gelatin in 1 quart of water, or by adding 1/4 teaspoon of salt and 1 tablespoon of sugar to 1 pint of water. A product for infants, Pedialyte, provides the right amount of electrolytes for children, but endurance athletes have used it and similar ones for years.
Exercising in the heat
To reduce the risk of heat injury, physical activity in elevated temperatures should be accompanied by preventive measures such as proper fluid intake and readily available first aid. Thermal stress during exercise can affect anyone, regardless of age, fitness level, body type or area of residence, and anyone can experience some form of heat stress while exercising. High environmental temperatures and a high relative humidity should be avoided, if impossible. Exercising in a hot environment causes a higher heart rate and reduced stroke volume. This is primarily due to two blood circulation factors: delivering oxygen to the working muscles, and delivering heated blood from the organs and muscles to the peripheral areas . The results of overstressing this system include a decrease in performance, heat injury or both. Therefore, under these conditions, either the thermal stress or exercise level must be reduced. During high ambient temperature s , body heat cannot be sufficiently lost. Heat exchange by evaporation of moisture on the skin is impaired further during humid, windless weather. (Perspiration alone does not cool the body. It is the evaporation of the moisture that carries heat off).
The ACSM Resource Manual contains guidelines for low-, moderate- and high-heat stress conditions (see Table1). Events/exercise should be cancelled or modified if they fall under the “high” heat-stress category. If not cancelled, it is vital to provide the necessary medical staff and equipment, a s well as plenty of hydration fluid.
Heat stress can creep up slowly. Larger body size and higher percentage of body fat can put a person at greater risk . Aerobic conditioning, level of acclimation and exercise intensity relative to the individual’s maximal work capacity are also factors that contribute to heat stress. Restrictive, heavy or rubberized clothing a d d weight and prevent evaporation of moisture. This can be dangerous regardless of ambient temperature. Most heat ailments can be prevented by increasing fluid and electrolyte intake, and modifying the environment. Dehydration can also significantly contribute to other heat-stress injuries, particularly if the activity is continued. Early symptoms include decreased urine output, lethargy, anxiety and/or irritability. Se v e re dehydration can cause uncoordinated gait and spastic muscle movement, as well as altered consciousness. This can lead to cardiovascular collapse and ultimately death.
Heat stroke
Dehydration can lead to heat exhaustion, which can progress to heat stroke. Common symptoms when dehydration progresses to heat exhaustion include “goose bumps” on the skin, dizziness, headache, shortness of breath, vomiting and/or uncoordinated gait. Body temperature is typically elevated, but less than 103 degrees Fahrenheit. Heat stroke symptoms are similar to those of heat exhaustion, and they are often difficult to differentiate. Heat stroke causes the body to lose its ability to therm or regulate. (It is important to note that younger, highly trained individuals may continue to sweat, but will exhibit central nervous system symptoms during a heat stroke.) It actually takes evidence of biochemical markers in the blood for an ultimate diagnosis of heat stroke.
Heat stroke is a medical emergency. For individuals directing exercise, it is not critical to distinguish between the various heat stresses. What is critical is the initiation of appropriate cooling and rehydrating procedures. Symptoms of any of these conditions (possibly with the exception of heat cramps) should be followed up with medical attention. If heat exhaustion or heat stroke is suspected, immediate medical attention should be sought by activating the EMS and your facility’s emergency procedures. For either condition, perform the following actions:
• Remove excess clothing.
• Remove the person from the heat-stress environment.
• Elevate the feet above the head.
• Wet the skin and provide fanning or total emersion in cold water. Packing the axilla (armpits) and groin areas with ice works well if total emersion is not possible.
• If conscious, provide cool fluids by mouth.
Be vigilant
Severe dehydration, heat exhaustion, and heat stroke are true medical emergencies, and the “wait and see” philosophy will spell disaster. They usually require hospitalization and intravenous fluids, and heat stroke can cause cardiovascular collapse and even death.
Education is the key to prevention. Educate yourself, your staff, and your clients on the necessity to hydrate and prevent heat-related illnesses. Consider the ambient temperature and advise clients to avoid the “high-risk zone.” Also, advise them to allow 10 to 14 days for acclimatization to hotter environments. The ability to perform exercise in heat can improve by repeated exposure. Finally, exercisers should not rely on thirst as the barometer for hydration and electrolyte loss. “Drink early; drink often,” should be followed to achieve optimal wellness. FM
References:
ACSM’s Guidelines for Exercise Testing and Prescription, 5th ed. Williams and Wilkins, 1995.
ACSM’s Resource Manual for Guidelines for Exercise Testing and Prescription, 3rd ed. Williams and Wilkins, 1998.
Casa, D.J., L.E. Armstrong, S.J. Montain, B.S.E. Rich and J.A. Stone. National Athletic Trainers’ Association Position Statement: Fluid Replacement for Athletes. Journal of Athletic Training 35(2):212-224, 2000.
McArdle, K. Exercise Physiology: Energy, Nutrition and Human Performance, 4th ed. Williams and Wilkins, 1996.
Stephen A. Black, M.Ed., P.T., A.T.C/L., N.S.C.A./C.P.T., director, Health and Fitness Institute, Stamford, Conn., and CEO of RockyMountain Human Performance Center Inc., Boulder, Colo., provides individualized programs for athletes, weekend warriors and post-rehab clients. Black has 20-plus years’ experience in the health and wellness industry, and has worked with professional teams including NFL, NBA, NHL, WNBA and ABL/NBL affiliates. He is also a presenter for the health and wellness industry.