Doctors may never know precisely what killed open water swimmer Fran Crippen, the 26-year-old who died during a race in Abu Dhabi over the weekend, but they agree that strenuous exercise in hot water could result in fatal heat stroke.
Had a safety boat been near the elite swimmer when he lost consciousness, he might have been cooled down and been saved, they say.
"It's pretty straightforward -- he died of one of two things," said Dr. Mark Morocco, associate professor of emergency medicine at the UCLA School of Medicine.
"He drowned of a cardiac arrhythmia or he died of drowning because he passed out," said Morocco, who has never treated Crippen. "Both were directly related to over-exertion, which is a terrible garbage-can diagnosis and does not speak to what happened."
"In the age of kayaks, jet skis and outboard motors, this sort of thing should never happen to an elite swimmer," he said. "No one was there to help him up out of the water."
USA Swimming said Monday it would commission a full, independent investigation into Crippen's death.
Some earlier reports indicated that the Olympic-bound athlete died of a heart attack. The findings of an autopsy by local authorities have not been released. And even that may not give definitive answers.
Heat stroke, for example, could only be determined if doctors got an internal body temperature right after Crippen died. His body wasn't found until two hours after the race ended -- about 400 meters from the finish line.
The International Swimming Federation (FINA) said doctors ruled the cause of death as severe fatigue.
Crippen's sister Maddy, herself an Olympic swimmer, told "Good Morning America" that her brother had been voicing concerns for months about inadequate safety.
A native of Philadelphia, Crippen was "fit as a fiddle," according to his former high school coach from Germantown Academy, Richard Shoulberg.
Crippen had told Shoulberg just 12 hours before the race that the outside temperature was 100 degrees and that the water was 87 degrees. Several swimmers complained of dehydration and disorientation and three were taken to the hospital.
"l have heard lot people complaining about the water being too warm," said Bill Volckening, a former editor of Swimmer magazine for U.S. Masters swimming. "There are some dangers of hyperthermia that have not really come to light yet and I hope there is some major reform in the sport of open water swimming with regard to safety."
Volckening, who knew Shoulberg as a high school swimmer, said the coach's athletes were "extremely smart, extremely savvy and extra well prepared."
"I don't have a good opinion of FINA -- they mismanage anything that comes their way," he said.
Fran Crippen Consumed Caffeine Gel Packs
Those who trained with Crippen said he also used GU energy gel a replenishing liquid that contains high amounts of caffeine. The swimmer reportedly consumed 10 to 15 packs during a typical two-hour swim.
Michael Sabala, assistant women's swimming coach at Columbia University, attended a summer training camp with Crippen and wondered if the caffeine, combined with the heat, could have contributed to Crippen's death.
"Elite athletes push themselves to the very edge," he said. "If there is a new edge, they don't know when they are about to fall off."
Open water swimmers keep gel packs in their bathing suits and drink them at intervals during the race. They are also used commonly by marathon runners and cyclists.
"Fran even talked at camp about how many calories he would consume," said Sabala. "He would cut them on the side and roll on his back and down it and swallow it then throw it in the water."
Some flavors contain 20 to 40 milligrams of caffeine. "That's like five cups of coffee in two hours in the 100-degree heat," he said. "No one is talking about that."
Jeff Konin, an athletic trainer and vice chair of orthopedic and sports medicine at University of South Florida, said, "I have tried GU myself."
"But I've not heard of anyone taking that many before," he said. "Anything in larger doses -- even vitamins -- can be toxic to the body."
Doctors say caffeine is generally "pretty safe."
"It's probably not that likely, but certainly a possible factor in the picture," said Morocco. "Caffeine can cause arrhythmias in sensitive individuals."
The more likely cause of death was hyperthermia, which led to heat stroke.
"During physical exertion as the muscles are working, part of the byproducts is heat, like a power plant," said Dr. Ted Benzer, chief of clinical operations in the emergency department and attending physician at Massachusetts General Hospital.
"The challenge is to get rid of the heat and the body doesn't have that many ways to do that," he said. "The human body underwater is not like a fish or a whale. The primary way it releases heat is through evaporative losses like sweating."
Sweat on the surface of the body creates a cooling effect on blood just under the skin. Unlike a dog, humans can't pant to get rid of the heat.
Heat stroke is seen from time to time in marathon runners during hot weather.
"It is an intriguing concern that [Crippen] had major exertion submersed under very hot water," said Benzer. "But this is very unusual -- I have never seen this in all the years I have worked in emergency medicine."
Heat Stroke Can Cause Confusion, Delirium
When the body's temperature reaches 106 to 107 degrees, it starts to cause death of tissue and organ failure.
One of the first warning signs is confusion and delirium as the brain begins to dysfunction. If not treated by cooling the body down, it can cause death.
"It's hard to say what happened," said Benzer. "Who knows who was watching and how closely. Basically, he may have become confused and his actions might have been unpredictable. Maybe he started getting heat stroke, was delirious and then drowned."
But doctors say there are other conditions that can cause sudden death in a young athlete -- heart valve problems, an electrolyte imbalance, congenital thickening of the heart muscle, cerebral aneurysms and even undetected arrhythmias like long QT syndrome.
"He could have been kicked in the head or had a neck injury and drowned," said Dr. Eric Coris, associate professor of orthopedics and sports medicine at the University of Southern Florida.
"But the number one thing that kills athletes is cardiac," he said. "You think heart first."
UCLA's Morocco agrees that many of those medical events could have been treated had there been more attention paid to safety.
"A lot of the responsibility is on the folks who put the race together," he said. "When you are 500 feet in the water, you are as far away as being in wilderness 20 miles in Yosemite. If you don't have someone in a rescue boat, you are in trouble. Anything can happen."
"The other problem is elite athletes are not very good patients," said Morocco. "They don't want to get out of the race, even if they feel poorly. They are well-trained, but are also pressured to perform. Oftentimes a great athlete cannot advocate for himself. But those running the race should advocate for him."