On a warm Tucson evening in July 2006, Tom Boyle was driving home when he saw a cyclist crushed underneath the front wheels of a car. With the 18-year-old screaming in pain, Boyle jumped out and lifted the car above the trapped cyclist before yelling to the driver, who then pulled him out.
It was only when driving home that Boyle realised he had clenched his jaw so tightly during the lift he had broken eight of his teeth.
Boyle had accessed a phenomenon known as "hysterical strength". Normally inaccessible, this force can come to the fore in life-or-death circumstances. Documented cases have been detailed in a new book Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance, which gives a gripping insight into the mind of great athletes, adventurers and peak performers to find out what gives them the capacity to push harder and achieve more.
With January in full fitness swing, author Alex Hutchinson believes we all have the potential to get more from our exercise routine than we give ourselves credit for.
Speaking this weekend to the Sunday Independent, Alex describes endurance as "the struggle to keep going against that mounting desire to stop - to hold your finger in the flame", and says many top athletes actually enjoy the physical torture: "The most successful tend to have a streak of what we call 'benign masochism'," he says. "For whatever deep dark evolutionary reason, they get satisfaction from seeing how much pain they can handle. It's hard to know how much of this is nature or nurture, but we do know there are certain genes from hunter-gatherer times, which cause people to seek out new experiences, to wander and create challenges and risks."
For those who don't have the "benign masochist" streak, Alex has a number of principles to break through to their personal best:
Limits are in your head
The four-minute mile is a classic example of how possible or impossible you view a task can directly influence success. For more than 100 years, people tried and failed to break the four-minute mile. When Roger Bannister did it, scores of runners quickly followed suit. It's not that it became physically easier to run. It was that Bannister proved it possible and allowed others to overcome the mental block in their own mind.
What the man who pushed himself to death can teach us about endurance
In January 2016, Henry Worsley died of organ failure during a solo expedition across the Antarctic. His death wasn't caused by cold, hunger or injury. He had pushed himself to death.
But what really piques scientists' interest is not that one or two people die in such circumstances - it's that the majority don't. The improbability of pushing yourself to death, in the view of scientist Tim Noakes, is evidence that our brains are hard-wired to impose protective limits.
We all possess a finishing kick
Ever notice those desperate sprints to the finish after long and gruelling races? If our limits of endurance are defined by a maxed-out heart, insufficient oxygen and fatigued muscles, why are we able to speed up? The answer, according to Noakes and others, is that this finishing sprint reveals the presence of an untapped physiological reserve, only released when the "danger" of the race is nearly over and we can try extra-hard.
Samuele Marcora tested a simple self-talk intervention and had 24 cyclists test to exhaustion. He gave half simple guidance on how to use positive self, including using certain phrases early on ("feeling good!") and others later in a race ("push through this!").
The self-talk group lasted 18pc longer than the control group, and their rating of perceived exertion climbed slower throughout the test.
Encourage others, encourage yourself
Even someone's smile of encouragement can help you push yourself harder. Researchers at Bangor University in Wales had volunteers pedal a stationary bike for as long as they could, while a screen in front of them flashed happy or sad faces in imperceptible 16-millisecond bursts. The cyclists who saw sad faces rode for less time than those shown happy faces and reported a lower sense of effort. It explains why constant encouragement and positive self-talk boost performance.
Stretching and training in a group
Researchers have found athletes who stretch alone do not perform as well as those who stretch in a group. The same can be said for working out alone.
Do it early - work-outs are harder after a long day in the office
Researchers put cyclists on a bike and asked one half to partake in a cognitively fatiguing task beforehand. After playing a computer game for 45 minutes, they performed worse and claimed the level of effort was harder than those who hadn't, even though the game was not physically challenging.
It's how you feel about the heat that counts
When athletes don ice-filled vests and drape ice towels over their necks, it doesn't alter their core temperature, but influences how hot they feel - and that dictates how hard they are able to push.
In a 2012 study, cyclists in a heat chamber were told to pedal under a thermometer that read 32C, then told to pedal again before a reading of 26C - but scientists never lowered the temperature. The result? They went faster.
As a rule athletes have a higher pain tolerance but crucially share the same sensitivity to pain. So it's not that the best don't feel it - they just develop better coping techniques.
You have to find what motivates you, learn what gives your workout meaning and learn to distract yourself by thinking about that. The challenge is to learn to tune into your body and dig into a certain level of discomfort for a little while.
Endure will be published on February 8