At 336 pounds, Minnesota Vikings lineman Korey Stringer was a massive presence on a football field, but the size that helped him become All-Pro last year put him at great risk of heatstroke during intensive summer workouts.
The handful who have died of football-related heatstroke in recent years, say experts, have generally weighed at least 250 pounds.
"Big men have a lot more muscle, and they make a lot more heat," said William Roberts, a Minneapolis-area physician active in the American College of Sports Medicine. "A big man probably has a thicker body-fat layer, so it's harder to get rid of the heat," he said. "He was working hard in extremely hot and humid conditions."
High humidity means that sweat does not evaporate and cool the body, leaving the heat to build up internally until it damages organs. Pads and helmet also trap heat.
Sports medicine specialists questioned why the Vikings did not order Stringer off the field after he vomited repeatedly, a warning sign of heatstroke. Stringer did that three times but resumed playing each time. Only at the end of the practice did he request assistance and show his next obvious symptom, disorientation.
"You'd think the second time would be the alarm, but I don't know his workout patterns," Roberts said. "He may have been somebody who vomits off and on in practice when he is working hard. There are people like that."
But Robert Cantu, medical director of the National Center for Catastrophic Sport Injury Research at the University of North Carolina, said it was a clear-cut signal.
Doctors note that a heat stroke victim then experiences profound fatigue, headache, dizziness, irritability and muscle cramps.
Once body tissues reach 106 degrees, organs start to shut down, often starting with the brain and systems that control the body's internal thermostat and its ability to perspire to get rid of the internal heat, doctors say. In most cases, the central nervous system derails and can cause hallucinations, confusion, disorientation and coma.
Then liver and kidneys start to fail, the heart pumps inefficiently and internal bleeding can occur.
When Stringer got to training camp this year, he was at the lowest reporting weight of his career. Doctors said, though, that daily weight fluctuations are more important. A player can safely lose 3 percent of body weight through sweating each day, but a 5 percent loss is dangerous.
Sports medicine specialists said available information should have helped avoid such a death. But this summer there have been two. On Sunday, University of Florida freshman Eraste Autin died of complications six days after he went into a coma after a practice.
Cantu said coaches, doctors and players have been told to acclimatize athletes to heat gradually when practice begins, track heat and humidity, allow frequent rest, give players unlimited quantities of chilled water and encourage them to salt food but not take salt tablets.
They have been advised not to use full gear -- as much as 35 pounds -- in high heat.
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