"It's remarkable, but it's also explainable," said Mike Tipton, a professor of human and applied physiology in extreme environments at Britain's University of Portsmouth.
"If I was going to design somebody to be able to swim in cold water, I would get somebody who is big, [with] lots of muscle [and] lots of subcutaneous fat."
In short, a retired professional fullback is "the right size, the right shape" and "he was in reasonable water temperature".
Konrad's story has provoked expressions of disbelief. The Florida Wildlife Commission is investigating. If it corroborates Konrad's account, there are lessons here for us all.
It's pretty easy to imagine some aspects of Konrad's predicament when, as he tells it, a wave hit his 11m vessel as he was tending to a fishing line about 12.30pm local time last Wednesday and threw him overboard. He had no lifejacket, no water, no food, no way to keep warm and nothing with which to signal rescuers. His boat, which was on autopilot, headed off toward Grand Bahama Island. (It was later found on Deadman's Reef. Not making that up.)
He swam to Palm Beach, covering 43.5km before ringing the doorbell of an oceanfront home for help at 4.30am the next day.
While at sea, Konrad faced challenges most people wouldn't think of. For example, going in the right direction is difficult even for experienced open water swimmers.
"Nobody in the world swims straight," Munatones said. "That's why there are black lines on the bottom of the pool."
Konrad may have been able to get his bearings from buildings on shore, if he could see them, he said. And once the sun set, onshore lights would have helped guide him in.
Then there's the initial shock to the heart and uncontrolled breathing that result from plunging unprepared into cold water. "Sixty per cent of those who die [in water] below 15C die in the first minutes of immersion," Tipton said. But at 20C, it was easier for Konrad to avoid that.
Conventional wisdom is that someone in Konrad's predicament should stay still rather than try to swim if the water is colder than 25C to preserve core heat and ward off hypothermia, Tipton said. But a big, fit person with both muscle and a good layer of subcutaneous fat was probably better off going for it, he said.
Ideally, he would use a slow stroke that generated some heat but not too much. (Konrad said he alternated between breaststroke and backstroke). A swimmer's chance of survival in 20C water for eight to 10 hours is about 50 per cent, he said.
"There's a balance between heat generated and heat lost," added Mark Harper, who studies survival in extreme situations with Tipton. "Using your muscles does generate heat. However, using your muscles also sends much more heat [away] from the [vital body] systems."
Dehydration and lack of food would be survivable for 16 hours, Tipton said, though, according to Munatones, people trying to swim the English Channel normally take in fluids about every half hour. Also, salt in the water would have burned his eyes, mouth and nasal passages.
Favourable seas were essential.
"There's no way an untrained person could swim for that long," Munatones said.
And then there is the psychology of survival. Interviews with survivors show they maintain the conviction that they're going to make it and avoid "learned helplessness" that can overwhelm someone clearly facing death, Tipton said. Many, he said, conjure mental images of their children -not their spouses or any other family.
"They're swimming as if they're going to rescue their kids," he said.
"It's a remarkably powerful motivator."
Konrad nailed that one, too. He spent time thinking about his 8- and 10-year-old daughters and resolved to get home alive.
"After some time I just said, 'Look, I'm not dying tonight, I'm going to make it to shore,"' he said. "It certainly tests your mind when you're in the water that long."
