An Australian 13-year-old who swam 4km (2.49 miles) to shore and then ran 2km (1.24 miles) to get help for his stranded family has been described as “superhuman”.

Experts say Austin Appelbee’s feat of endurance exceeded the limits of what is normally perceived as possible. So how was the teenager able to save the day, and is there any precedent for it?

What happened to Austin Appelbee’s family?

Austin and his family were on holiday in Quindalup, 200km (124 miles) south of Perth, when strong winds pushed their inflatable paddleboards and kayak offshore from Geographe Bay on Friday afternoon.

His mother, Joanne Appelbee, told him to swim ashore to seek help, telling the ABC: “I knew he was the strongest and he could do it.”

Initially setting off in a kayak, Austin had to abandon the vessel after it took on too much water in the rough conditions. About two hours into his four-hour swim, he ditched the lifejacket he was wearing.

“I was very puffed out but I couldn’t feel how tired I was,” he said.

“I just keep swimming, I do breaststroke, I do freestyle, I do survival backstroke.”

Once he had swum the 4km (2.49 miles) to shore in fading light, the teenager ran 2km (1.24 miles) to his family’s accommodation, using his mother’s phone to call emergency services at about 6pm.

“I said, ‘I need helicopters, I need planes, I need boats, my family’s out at sea.’ I was very calm about it. I think it was just a lot of shock.”

After the call, he passed out from exhaustion and was taken to the hospital. His family was rescued floating about 14km (8.7 miles) offshore. Austin was given crutches to help his sore legs bear his weight, the ABC reported.

How did the 13-year-old swim and run that far?

Prof David Bishop, a muscle exercise physiologist at Victoria University, said fight-or-flight situations can enable athletes – and ordinary people – “to go beyond what their perceived limits are”.

There have been other reports of preternatural strength. In 2013, two teenage girls in Oregon reportedly lifted a 1,360kg tractor off their father’s chest; in 2016, another US teenager was said to have lifted a car to save her father, while a 16-year-old reportedly did the same for a neighbour in 2019.

The phenomenon has sometimes been referred to as “hysterical strength”, though the origins of the term is unclear.

In a 1961 study, researchers found that people were immediately stronger at a forearm flexion task when frightened, after shooting a starting pistol next to participants’ ears without warning.

Anthony Blazevich, a professor of biomechanics at Edith Cowan University, said the release of fight-or-flight hormones had an impact.

“If you get highly motivated, if you have some fear, you’re going to be releasing adrenaline, noradrenaline, other stress hormones like cortisol, which dump a whole bunch of sugar into your blood,” he said.

“These things really help you do somewhat brief activity, from seconds up to minutes or potentially even tens of minutes.”

But for activities lasting hours – in the case of Austin’s swim – “eventually these systems do get depleted”, Blazevich said. The periods of recovery afforded by survival backstroke – a swimming style aimed at conserving energy – may have been critical, particularly in saltwater, where floating was relatively feasible.

Some experts argue that endurance is an issue of mind over matter. Prof Samuele Maria Marcora, an exercise scientist at the University of Bologna, has shown mental fatigue can impair physical performance, while other research has found endurance performance is improved by using imagery, self-talk and goal setting.

“I was just thinking in my head: I was going to make it through, but I was also thinking about all my friends,” Austin said of his swim. “I have to keep on going.”

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Teenage boy’s 4km swim to shore to save family captured in aerial footage – video

Bishop said: “[Austin] had a base of swimming fitness and physiology that allowed his strong mind to go beyond the limits”

“It’s an amazing feat.”

Was age a factor?

Blazevich’s research has shown that children can perform as well as highly trained adult endurance athletes. In a study comparing 10-year-old boys with 21-year-old men during high-intensity cycling, he found the children outperformed most adults.

“What kids do is recover incredibly rapidly, as good as elite endurance athletes,” he said.

However, adults have larger hearts and lungs, and central nervous systems that do “not seem to fatigue as fast”, he said.

“This is probably why kids play on an intermittent basis … They run, stop, run, stop, but they do it all day,” Blazevich said.

Austin told the ABC he had started swimming lessons when he was four – but had previously found it “quite tiring” to swim 350 metres without a break.

Are there similar feats of survival at sea?

Other incidents of unintended aquatic endurance have previously made headlines around the world.

In 2013, South African man Brett Archibald was found after falling overboard a surf charter in the Indian Ocean and treading water for more than 28 hours.

Austin’s remarkable swim has parallels with the story of the Syrian refugee Yusra Mardini, who as a teenager in 2015 swam for over three hours to reach the island of Lesbos – pulling with two others their migrant boat, after the dinghy began to take on water in the Aegean Sea.

And in 2024, a Chinese woman was rescued 80km off the Japanese coast, buoyed up by a rubber ring, after being swept out to sea and spending two nights in the ocean.