Strenuous exercise, high temperatures and humidity can be a risky combination. This is especially true for young athletes who lack the experience to know when they need to take a break. Jay Hoecker, M.D., a pediatrician at Mayo Clinic, Rochester, Minn., offers parents and coaches insight into heat-related illnesses and ideas for preventing these events.

Some people say heat exhaustion. Others say heatstroke. What's the difference?

Three heat-related illnesses can affect children and teenagers: heat cramps, heat exhaustion and heatstroke.

The least serious of these is heat cramps, which are painful involuntary muscle spasms. These cramps are brief — usually lasting only minutes. They occur most often in the muscles being exercised, such as the calves of your legs or the muscles in your arms. Heat cramps are more likely to occur when your child hasn't taken in enough fluids before and during practice.

Heat exhaustion is more serious than heat cramps. If you have heat exhaustion, you'll experience a rapid heart rate, low blood pressure, and heavily sweating skin. You may look very pale and feel faint and nauseated. As with heat cramps, lack of fluids contributes to the problem. If your child exhibits these signs and symptoms, and seems confused or irritable, he or she may have heat exhaustion.

Heatstroke is the most serious condition. Like other heat-related conditions, inadequate fluid intake and heavy exertion in hot weather are factors. Unlike the others, heatstroke is life-threatening because your body loses its ability to sweat and regulate temperature. As a result, your body's temperature can reach 106 F or more, a point at which brain damage or even death is possible. Signs of heatstroke include rapid heartbeat, unusually high or low blood pressure, lack of sweating, fainting, rapid and shallow breathing, delirium or loss of consciousness.

Confusion about heat-related illnesses — such as not recognizing the warning signs or how serious the condition may be — can impair an athlete's judgment, causing him or her to continue rather than stop and get help. Let your children know that if they feel very hot and become dizzy or confused, they must stop playing and tell a team coach or trainer right then, rather than trying to tough it out.

How common are heat-related conditions in children? In what activities do they occur most often?

Heat-related conditions are more likely to affect preteens and teenagers who participate in organized, competitive, strenuous aerobic activities. If your child runs in hot weather or suits up for summertime football practices, for instance, a heat-related illness may be more likely.

What should I do if my child seems hot or looks ashen after practice?

You can relieve heat cramps by gently massaging the affected muscles. Giving your child a cool drink will help, too. Water is your best bet. There's no need for salt tablets for simple dehydration. Excessive salt intake can lead to hypernatremic dehydration, a condition in which the body not only is short of water but also carries an excess of sodium.

If your child looks ill, you'll want to cool him or her down and start rehydration. Bring your child to a cool room or shady area to rest. Provide cool, but not icy, water or a sports beverage containing electrolytes. If your child is dizzy or feels nauseous, have him or her lie down, with feet slightly elevated. Directing a fan onto your child also may speed cooling. If your child is experiencing heat exhaustion, he or she will feel better after cooling, resting and becoming hydrated.

Also be sure to take your child's temperature. If the temperature is unusually high, call an ambulance and have your child taken to the nearest emergency room. After calling the ambulance, you may want to call the emergency room to let them know your child will be coming in.

What can I do to protect my child from these conditions?

Make sure your child drinks fluids before, during and after physical activities. If the activity is strenuous and the weather is hot, aim for two to four glasses — 16 to 32 ounces — of water per hour of activity.

Teach your child to maintain fluids before thirst begins.

• Give your child a cold bottle of water or sports beverage to drink during practice.

• After practice, ask your child if he or she drank the full bottle.
• If your child didn't finish the water or sports drink during practice, encourage him or her to drink more water after practice.
• If your child or teen finished the bottle, have additional bottles of water or sports drinks available in case he or she is still thirsty.

If you carpool with several other parents, you may want to take turns bringing a small cooler with cold drinks. Children are much more likely to drink when cold water and beverages they like are at hand immediately after the activity.

Coaches can help prevent an athlete's dehydration by providing time out for water breaks. Drinking water is required and not just optional. Don't hesitate to ask your child's coach how he or she prevents team members from becoming overheated and dehydrated.

How can I tell if my child is dehydrated?

A rough hydration barometer can be the color of your child's urine. If it's clear or light yellow, hydration is likely to be adequate. But if the urine is dark yellow, dehydration is present. If dehydration becomes severe, other signs include:

• Lack of urination for eight hours or more
• Confusion or decreased alertness
• Muscle cramps
• Sunken eyes
• Excessive sleepiness
• Lethargy
• Weakness
• Dry skin
• Rapid breathing or quickened pulse

How soon after my child has fallen ill from the heat can he or she resume practice?

Practice may resume when your child is rehydrated. Signs of rehydration include:

• Thirst is satisfied
• Ability to produce urine returns
• Pulse is normal
• Mental state is alert and oriented
• Cramps have resolved
• Temperature is normal to the touch
• Fluid deficits have been replenished

An important note: Don't use thirst as an indicator of your child's state of hydration — it's too late. Proper hydration should be a proactive, preventive activity.