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From young women hoisting vehicles in dire circumstances to powerlifters heaving unbelievable loads, fits of hysterical strength do happen, but why?

Bobsleigh pilot Kaillie Humphries, right, and brakeman Chelsea Valois take off on foot down the natural ice track before huddling into their sled during the first run of the two-women competition at the 2013 bobsleigh and skeleton world championships in St. Moritz, Switzerland.

Canadian strongman and powerlifter Tom Magee labours to raise a 350-pound stone at the 1986 Commonwealth Highland Games in Edinburgh. Zoran Milich/The Globe and Mail

At the 1983 World's Strongest Man competition, in Christchurch, New Zealand, a fresh-faced Canadian powerlifter named Tom Magee, later known as MegaMan during a brief World Wrestling Federation career, deadlifted 535 kilograms of local cheddar cheese – "enough," the television commentator deadpanned, "to fill an awful lot of mousetraps."

Thirty-five years later, that feat remains the heaviest deadlift in the books. Yet local news sources regularly report seemingly greater performances out in the real world – such as that of Nick Williams, the Newfoundland man who lifted a four-wheel-drive vehicle high enough for a young boy to be pulled from under its tires in 2015, or Charlotte Heffelmire, a 19-year-old Virginian who hoisted a burning GMC truck off her pinned father that same year. What Mr. Williams and Ms. Heffelmire may have tapped into is the stuff of legend – a well of superhuman strength that can only be drawn on in moments of crisis or extreme passion.

So could Tom Magee have put the record well and truly out of reach if there had been a helpless child trapped under all that cheese?

Over the next few weeks, we'll be pondering a version of that question as we marvel at feats of otherworldly strength and Olympian endurance on the slopes and in the arenas of Pyeongchang, South Korea. Athletes such as bobsleigher Kaillie Humphries, in search of an unprecedented third consecutive gold medal, will hope the heightened emotion of the Olympic spotlight will enable them to perform feats they couldn't possibly achieve in any other context. In sports, it's called a clutch performance; in other contexts, it's sometimes called "hysterical strength." Is it real? After more than a century of debate, scientists still aren't sure, but a growing body of evidence suggests our apparent physical limits are more elastic than they seem – and, like Olympians, we can learn to dip into those reserves.

Swimmer Penny Oleksiak competes in a women’s 100-metre butterfly heat during the 2017 world championships in Budapest. Clive Rose/Getty Images

The idea of hidden strength has a long history. Viking sagas from more than 1,000 years ago, for example, tell of berserkers whose wild fury "doubled their strength and made them insensible to bodily pain," thanks to the bear gods or, some modern scholars believe, drugs. Other tales report that people with mental illness and swimmers on the verge of drowning can wield unstoppable strength that is impossible to reproduce on demand.

However, it was only in the late 18th century, when Luigi Galvani began using electricity to make frogs' legs twitch, that the tools to test this idea became available. When the same technique was tried on humans, early volunteers were convinced electrical shocks made their muscles stronger. "Everyone who has experience having his muscles stimulated by electrical stimuli knows that it is possible in this way to obtain contractions of a force which is quite impossible to reproduce voluntarily," a pair of Danish researchers wrote in 1923.

Actually measuring this extra strength was challenging, though, because real-life human movements generally involve the co-ordination of multiple muscle groups, while electric shocks stimulate just one muscle at a time. When an eccentric British physiologist named Patrick Merton eventually rigged up an apparatus to test a single thumb muscle in 1954, his self-experiments showed that painful electric shocks could produce no more force from the muscle than his own voluntary contractions. The electrically stimulated contractions felt far stronger, but this was just an illusion, and subsequent experiments have mostly corroborated this finding.

But in the Soviet Union, meanwhile, Olympic weightlifting coaches were reaching a different conclusion for complex movements requiring multiple muscle groups. Vladimir Zatsiorsky, a biomechanics expert at the Central Institute of Physical Culture in Moscow, eventually published data suggesting that, in this context, most of us can summon just 65 per cent of our theoretical maximum strength, while elite weightlifters can squeeze out 80 per cent in practice, plus an additional 12.5 per cent – but only in big competitions.

How did the Soviets come up with these figures? When I contacted Dr. Zatsiorsky in 2016, he was 83 years old and retired from Penn State, but still actively publishing research. He couldn't, however, fill in any details about his much-quoted maximum-strength numbers. "Unfortunately," he told me, "I do not remember who mentioned these facts first."

Still, the performance-boosting effect of big competitions rings true to experienced lifters such as Tom Magee. "These big lifts were done with extreme passion and emotion," he explained when I reached him in Los Angeles recently to ask about his record-setting cheese lift. "I could lift far more that way, but it took a lot out of me."

As for the news stories about people lifting cars, Mr. Magee pointed out that they're not as far-fetched as they may seem – and he himself had sometimes performed the feat. Depending on the weight distribution of the car, the axle design, the suspension stiffness and other mechanical factors, you can hoist one end while lifting considerably less than half the car's total weight. "The edges of cars are usually very handy to hang onto," he added. "This helps."

Physics aside, Mr. Magee said, the key to these lifts was the "mind-endocrine link," his term for the connection between mental processes and kid-trapped-under-a-car hormonal responses: "I cultivated the ability through certain thought rituals to naturally release adrenalin into my system." That's consistent with a notorious 1961 study in which researchers saw a 6.5-per-cent increase in strength following injections of adrenalin – comparable, as it happens, with the 7.4-per-cent boost they saw when one of the experimenters snuck up behind the subject and fired a starter's pistol in his or her ear immediately before the lift.

In Pyeongchang, that mental component may be most important in longer events such as cross-country skiing and speed skating, according to research by physiologist and former elite skier Guillaume Millet, who heads the University of Calgary's Neuromuscular Fatigue Laboratory.

Dr. Millet has studied competitors in some of the longest and most gruelling endurance races on the planet, using sophisticated modern versions of Prof. Merton's muscle-twitch apparatus that can distinguish between fatigue in the muscle itself and fatigue in the central nervous system. When you get tired, the signals travelling from your brain along your spinal cord and then to your muscles get weaker – even if you're still trying as hard as you can. The longer the race, he has found, the greater the role of the brain.

American Bob Beamon is seen breaking the record for men’s long jump at the 1968 Olympic Games in Mexico City. Mr. Beamon’s gold-medal jump was the first to surpass 28 feet. Tony Duffy/Getty Images

For example, competitors in the Ultra-Trail du Mont-Blanc, a 166-kilometre ultramarathon race through the Alps, typically lose 35 per cent to 40 per cent of the maximum strength in their legs by the end of the course. But only about 10 per cent of that loss is attributable to muscle fatigue; the rest is a result of weakened signals from the brain.

Puzzlingly, in the even more extreme Tor des Géants race, which covers 330 kilometres in the Italian Alps, competitors only lose about 25 per cent of their prerace leg strength. "Okay," Dr. Millet jokes, "so, if I run 200 miles, I'm less fatigued than if I run 100 miles!" The limits these competitors are facing, in other words, aren't simply a matter of maxed-out muscle.

For Olympic athletes, all of this adds up to the conclusion that mastering the mental side of performance involves more than just conquering nerves or staying focused – it's also about learning, as Tom Magee did, to dip into normally inaccessible reserves of strength and endurance. That can be as simple as controlling your internal monologue through self-talk training, so the words echoing through your head when the stakes are highest are, "You're ready for it!" rather than, "This hurts!"

The self-talk doesn't slow your heart rate or make your muscles any less tired, but it alters how your brain interprets these signals – and, as a result, your brain remains willing to keep sending strong signals to your muscles. In a 2016 study by Brock University physiologist Stephen Cheung, just two weeks of self-talk training boosted endurance time from eight minutes to 11 minutes in a cycling test in a heat chamber.

This is an approach that we can all implement – and that the best athletes in the world have already mastered, either intuitively or through hard work. After all, Ms. Humphries's answer to the prompt "If I weren't an athlete, then I would be …," in a pre-Pyeongchang get-to-know-you questionnaire administered by the Canadian Olympic Committee, was no coincidence: "sport psychologist."

Adapted from Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance, by Alex Hutchinson (HarperCollins, Feb. 6, 2018).