The third leading cause of death in athletes is heat illness.
It can be difficult to prevent because sometimes players show no signs of a problem until it's too late.
Now technology invented for NASA is helping players on the football field. It's a coach's job to push hit athletes, but how do you tell when a good practice turns dangerous?
Overheating can be fatal. It killed NFL player Korey Stringer and a freshman football player in Florida in 2001. That's why Coach Jim Leavitt from the University of South Florida had his players test a new technology to reduce heat illness in athletes.
Ten players, the bigger, at-risk guys, swallow a capsule about two hours before practice. The pill which contains a battery and an electronic transmitter, travels into the intestines, so it isn't affected by the cold water players drink.
At practice, trainers hold an electronic sensor close to the players' backs and crystals inside the pill sense body temperature.
Through a radio-frequency signal, the pill transmits information, which is tracked on a laptop.
NASA developed the technology, called Cortemp, in the 1980s and doctors hope it will help them better understand how to keep athletes out of trouble in the heat.
The pills are taken daily and last in the players' system for about 24 hours, and each pill costs about $40.