Dehydration Part 1: How It Happens
Body Heat and Hydration
If a player is dehydrated, he or she may not initially know it.
As dehydration progresses, however, the player may start to show signs like a decrease in concentration and performance.
As dehydration continues to get worse and the internal body heat starts to rise, the player may also start to show signs of illness.
Heat-related Syndromes
The heat-related syndromes that may occur (in order of severity) include:
◊ Heat cramps (muscle spasms that result from the loss of a large amount of salt and water through exercise). They occur most often in the abdominal, calf, and thigh muscles. Signs include heavy sweating, fatigue, thirst, and muscle spasms.
◊ Heat exhaustion. Signs of heat exhaustion may include: a weak but rapid pulse, faintness, dizziness, headaches, fatigue, low blood pressure after you stand from sitting, muscle cramps, nausea, irritability, and/or cool, moist skin with goose bumps or pale color (in the heat).
◊ Heat stroke (body temperatures generally greater than a threshold of 40°C/104°F, a high fever - where the body's temperature regulating abilities are impaired). These individuals may be confused, be unable to think clearly, pass out, collapse, or even have seizures. Sometimes a person even stops sweating at this stage (skin is red, hot, and dry) and he or she may start to shiver. There may be throbbing headaches, nausea/vomiting, and a strong, rapid pulse.
Heat stroke requires immediate medical attention to prevent organ failure, brain damage, or even death. These individuals should be cooled down as soon as possible to lower the body's core temperature. It's the number of minutes above the critical threshold (40°C/104°F) that can lead to cell damage.*
* It is not unusual for some athletes to experience prolonged overheating without noticeable medical impairment, especially during competition [1]. It is important to keep an eye on the player's signs and symptoms to determine if intervention is required.
Some Common Risk Factors For Developing A Heat Illness*
■ High heat ■ High humidity ■ Players playing in hotter temperatures than normal ■ Players running at faster speeds than normal ■ Players with a history of heat illness ■ Loss of salt and water without proper replacement ■ Greater body weight ■ People with medical conditions (i.e. fever) or taking medications that impair the ability to sweat (most commonly, anti-histamines and medications for high blood pressure, heart disease, and depression)*
* The body's metabolism creates heat as a by-product of normal cellular reactions during increased work levels in sports. Heat levels can dangerously rise when the heat produced by the body continually outpaces the speed at which the body releases heat into the surrounding environment.
Immediate Treatment for Heat Illness
The treatment for heat illness includes actions like:
► call for emergency assistance (heat stroke)
► sit the player in the shade or in air conditioning
► douse the player with water and blow cold air on the player (in low humidity, wrap the player in a cool, wet sheet and fan vigorously)
► put the person in a cold bath or shower (if available)
► drink cold fluids
► loosen or remove clothing
► apply ice packs to the groin, head and neck, and armpits (if ice is available).
How to Avoid Itª
1. Drink plenty of fluids (water and/or sports drinks) before, during, and after the match or practice (scheduling frequent hydration breaks during practice sessions helps)
2. Avoid beverages containing alcohol or caffeine
3. Wear proper clothing or uniforms for the environment
4. Stay in the shade as often and as long as possible before, after, and, where possible, during the match
5. Use sun block lotion on exposed body parts
6. Splash your exposed skin surfaces with water before the match and during breaks
7. Get proper rest to increase temperature tolerance
8. Consider giving teams additional breaks if the measurement of thermal stress - Wet Bulb Globe Temperature (WBGT)* - is above 31°C**
9. Know your own health problems (i.e. asthma), including the side effects of any medications that you take
ª Remember: immediately seek help if you start to develop signs and symptoms.
* WBGT requires a special measuring tool (or tools) to evaluate humidity, solar radiation, wind speed, and air temperature. WBGT helps to more accurately determine the level of heat stress placed upon a player's body.
** For FIFA, additional cooling breaks 30 minutes into each half are allowed if the WBGT reaches its critical level (31/32°C) just before the match. For example, at the final of the men's tournament at the 2008 Olympic Games in Beijing, which was played at noon, there was a WBGT of 34°C at 11:30 a.m. and an additional cooling break was introduced into each half.
Sodium (Salt) in the Heat
Studies have shown that it's also important to take in sodium (which is a building block of salt) after 60 minutes or more of play (especially in hot, humid environments). For the body to absorb water properly, sodium is a necessary element. Of course, the amount of sodium required is relative to the individual and his or her amount of sodium lost.
How Much Sodium is in Your Sweat?
There are simple ways to test if you sweat out a lot of sodium:
◊ Players with white sweat stains on dark shirts (when the shirt dries) may already know they are at higher risk for sodium loss than other players. Please keep in mind that deodorant may also leave white stains on your shirt.
◊ Players may taste salt on their lips and sometimes irritation in their eyes when they sweat.
◊ Sweat patches (patches that collect sweat samples) may help players evaluate more accurately their levels of sodium loss (it requires laboratory assistance to analyze the sweat composition).
How Does The Body Regulate Heat?*
During exercise, the body increases blood flow to the skin to decrease the body's heat at its core, the body sweats, and we take deeper and/or faster breaths to help regulate body heat.
The four main methods of body heat regulation are:
► Evaporation (where surface liquid is converted into a gas and leaves the body's surface). In fact, cooling the body down is the main reason why we sweat. Evaporation also takes place as we breathe hot, moisture-filled air into the surrounding environment.
► Conduction (the transfer of heat between objects in direct contact with each other). Some examples: a hot player against a cold goalpost, an ice pack on the neck, and drinking cold water. You become cooler as the cold object becomes warmer. The speed of heat transfer increases with:
● a larger amount of surface area contact between objects
● a greater temperature difference between objects
● a lower efficiency of insulation between objects (i.e. a thin vs. thick towel over an ice pack against the skin).
► Convection (the transfer of heat by the movement of air or liquid as it passes the body's surface). Heat transfer here too is controlled by surface area contact (i.e. the amount of exposed skin) and temperature differences (i.e. cooler outside temperatures), but it is also affected by how fast the cold object is moving (i.e. faster wind speeds)
► Radiation (the transfer of heat via electromagnetic waves). Hot objects (skin) radiate heat to cooler surroundings (environment). The more total area of exposed skin, the more "heat" energy can radiate to a cooler environment via infrared radiation.
* Heat produced during intense exercise is 15-20 times greater than at rest, and can raise core body temperature by 1°C (1.8°F) every 5 min if no heat is removed from the body [3].
1. Armstrong LE, Casa DJ, Millard-Stafford M, Moran DS, Pyne SW, Roberts WO. Exertional Heat Illness During Training and Competition. Medicine & Science in Sports & Exercise, 2007; 39(3):556-572.
2. Dvořák, Jiří, et al., eds. F-MARC Football Medicine Manual, 2nd edition (Zurich, SWI: FIFA, 2009), 132.
3. Nadel ER, Wenger CB , Roberts MF, Stolwijk JAJ, and Cafarelli E. Physiological defenses against hyperthermia of exercise. Ann. N. Y. Acad. Sci, 1997.301:98-109.
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