Thornton said the new advice highlights the need better oversight in high schools, too. Many high schools have no athletic trainer and practices for many sports often take place without anyone trained in first aid present, he said.
"It's like dropping a kid off at a swimming pool with no lifeguard," he said.
Many of the athlete injuries cited involve a muscle-damaging condition called exertional rhabdomyolysis, rhabdo for short. Intense exertion can cause muscle cells to leak enzymes and protein into the blood. Symptoms include extreme muscle pain and dark urine. Severe cases can lead to kidney failure and sudden death.
Avoiding sudden, intense exertion and drinking plenty of fluids can help.
Reported cases include 13 University of Iowa football players hospitalized last year after a too-strenuous offseason weightlifting session and 12 Oregon high school football players treated in 2010 after an intense preseason workout.
"Working athletes longer and harder "is not exercising smart," said Holschen, the Chicago physician.
National Athletic Trainers' Association: http://www.nata.org
AP Medical Writer Lindsey Tanner can be reached at http://www.twitter.com/LindseyTanner
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