Summer can be especially brutal for athletes who push themselves despite the rising heat index. As we head into summer, athletes and their coaches need to be on the lookout for the three most common types of heat illness: heat syncope, heat exhaustion, and exertional heat stroke.

Heat exhaustion is the inability to continue exercise in the heat. Symptoms include fatigue, nausea, vomiting, chills, diarrhea, heavy sweating, irritability and headache. Heat syncope is dizziness caused by heat.

Exertional heat stroke, which is caused by elevated core temperature, can sometimes be fatal. The Minnesota Vikings' Korey Stringer died from an exertional heat stroke during training camp in 2001.

For Douglas Casa, the chief operating officer of Korey Stringer Institute and professor in the department of kinesiology at the University of Connecticut, there are five important steps all athletes should heed as the mercury rises:

1. Acclimatizing to heat. Give your body 7 to 14 days of gradually intensifying workouts to grow accustomed to the heat.

2. Proper hydration. During intense exercise in the heat, every additional 1 percent body mass lost in fluid makes the body a half degree hotter. Just a 2-3 percent loss can mean visible impairment.

3. Body cooling strategies. For instance, be prepared to take shelter when it gets too hot.

4. Add more rest breaks in warmer conditions.

5. Sleep. If you're well-rested, you're better able to tolerate heat.

"Athletes who are sick to begin with or who don't take appropriate time to acclimatize are at risk,'' said Sandra Fowkes Godek at the Heat Institute of West Chester University. ''It is important to listen to your body if it is telling you to slow down or stop."

Drink up, but ... Recognize that just drinking too much fluid after a too-tough practice can lead to hyponatremia, a low concentration of sodium in the blood.

Work it out: Start your training well hydrated, keep fluid loss at a minimum during the training and then replace any lost fluids afterwards. Calculate your sweat rate to determine what your body needs.

The Korey Stringer Institute provided this formula to calculate sweat rate: Every 2.2 pounds (or 1 kilogram) lost equates to 1 liter of fluid loss (sweat loss). Lose 5 pounds in 1 hour? Your sweat rate is 5/2.2 = 2.27 liters/hour.

Fowkes Godek says replacing about two-thirds of the loss right away is appropriate.

In an emergency:  An athlete with heat illness ideally should be immersed in ice water within 10 minutes of collapsing, according to the Korey Stringer Institute. If that's not possible, place the person in a shower, hose him off, or apply cold, wet towels to cool off as much of the body as possible. Once the cooling process has been started, call 911.

Read more Sports Doc for Sports Medicine and Fitness.