BALTIMORE (WJZ) — The cause of University of Maryland football player Jordan McNair was kept private until Monday. He was killed by a heatstroke.

Monday, the 19-year-old’s parents revealed the cause of his tragic death on a website for the foundation in his name.

May 29th — The offensive lineman’s final moments on the field lead to liver failure. And two weeks later, cost him his life.

On that May afternoon in College Park — temperatures reached into the low 80s — one of the hottest days of the year at that time.

Dr. Kevin Crutchfield of LifeBridge Medical says the summer heat — combined with high humidity — puts even the healthiest of athletes at risk of hyperthermia.

“If it’s 98 percent humidity, there’s nowhere for the water on your skin to go. It actually stays on your skin and acts as a thermal barrier, increasing the heat that your body retains because you can’t lose it.”  Crutchfield said.

And as workouts and practices for fall sports pick up — doctors recommend hydrating the night before — and to start slowly acclimating to strenuous activity in the heat.

“Now, in July, is the time for all these athletes wanting to play fall sports to get outside and exercise and start getting your body used to the heat.” Crutchfield said.

According to its website, the mission of the new Jordan McNair Foundation is to drastically reduce the number of heat-related deaths in athletes. His father wrote, “Our plans did not include his death. Our plans included something more. Our plans included him. But God had other plans.”

The University of Maryland hired a sports medicine consulting firm to conduct an external review of the team’s policies immediately after McNair’s death. It could take up to 90 days.

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