Frederick Mueller of the University of North Carolina at Chapel Hill says in 2007 two reported cases of high school football players dying of heat-stroke were two too many.

"There's no excuse for any number of heat stroke deaths," Mueller says in a statement.

Mueller, author of Annual Survey of Football Injuries -- a long-running compilation of statistics for 1.8 million middle school through professional team football players.

The symptoms of heat illness are nausea, incoherence, fatigue, weakness, vomiting, muscle cramps, weak rapid pulse and visual disturbances, but Mueller warns -- contrary to popular belief -- heat stroke victims may sweat profusely.

Mueller advises a medical examination for each player. Players with heat-related illness history are more susceptible to heat-stroke, as are overweight players. He suggests weighing players before and after practice. A 3 percent loss in body weight through sweating is safe. Five percent is in the danger zone.

Players need time to acclimatize to the heat when the season starts. Before, during, and after play, cold water as well as shaded cool down areas with circulating air should be provided.