A teenager whose collapse and death spurred a reckless homicide prosecution of his coach likely had a temperature of 109 degrees when he went down, a heat stroke expert testified Thursday.

Douglas Casa, an associate professor of heat and hydration issues at the University of Connecticut, said 15-year-old Max Gilpin's temperature stayed dangerously high for more than an hour before he began to cool down.

Casa also told jurors in the trial of former Pleasure Ridge Park football coach David Jason Stinson that eight to 10 players were showing signs of heat stroke during the 40 minutes of sprints the players ran on Aug. 20, 2008.

"No coach in American should have 40 minutes of conditioning without a mandatory break," Casa said. "How could you get water? They'd miss repetitions. The coach has to implement the guidelines."

Stinson is also charged with wanton endangerment stemming from the way he ran practice the day Gilpin, a sophomore offensive lineman, collapsed. Gilpin died three days later at a Louisville hospital. Stinson has pleaded not guilty to both charges.

Doctors at Kosair Children's Hospital in Louisville took Gilpin's temperature more than an hour after he collapsed and measured it at 107 degrees. Casa said any extended period with a body temperature over about 105 degrees can be harmful.

Generally, to save someone's life, their temperature must be brought down quickly, said Casa, who did not examine Gilpin, but reviewed medical records and statements made by other players to police.

"You have this 15 minutes you can save a life," said Casa, who is assisting Gilpin's family in a civil suit against Stinson and other school officials.

Jefferson Circuit Judge Susan Schultz Gibson ruled that Casa could speak generally about heat stroke and its causes, but could not say what caused Gilpin's heat stroke, nor give an opinion about the teen's cause of death.

Gilpin collapsed at the end of practice as players ran "gassers" — sprints from one side of the football field to the other — at the end of a three-hour practice. Players have testified that Stinson was angry about a lack of effort during practice and initiated the sprints as punishment.

Defense attorneys have described the practice as hard, but not outside the parameters allowed by the governing body of high school sports in Kentucky.