Earlier this year, Charlotte Heffelmire, a 19-year-old woman in Virginia, US, made headlines for a feat of superhuman strength: When her family’s garage went up in flames, she lifted up a truck to pull her father, who was pinned underneath, out of harm’s way.
It was impressive feat of strength for a woman who stands at 120 pounds (54 kg) — it’d be impressive for someone twice her size — but it’s also one example out of many. Every so often, a story will surface of a person who miraculously lifts a vehicle that no human would ordinarily be able to lift, saving someone pinned underneath.
It shouldn’t be able to happen, theoretically; a car on the smaller end of the spectrum weighs around 3,000 pounds (1360 kg), but the world record for a deadlift is just over 1,100 (499 kg), and the average man can maybe do around a fifth of that.
When people try to lift more than they can handle, one of two things happens: Either they tear a muscle or a tendon, or, more often, they do nothing — whatever they’re trying to pick up just stays on the ground.
But as the Heffelmires can attest, it happens nonetheless. In the BBC earlier this week, Adam Hadhazy broke down what scientists know about this type of superhuman strength, also known as “hysterical strength.”
The fear response works like this: When we’re faced with danger, our bodies run through a series of rapid-fire changes to make us stronger than usual. Fear stimulates production of the stress hormone cortisol, which increases blood pressure and blood sugar, giving you a burst of energy.
It activates the adrenal glands, which fill the blood with adrenaline and noradrenaline, two hormones that increase heart rate and breathing, sending more blood to the muscles and helping them to contract more easily. Adrenaline also decreases sensitivity to pain, helping us to focus on the threat at hand with minimal distraction.
But how does enhanced strength become so enhanced that you can lift something as heavy as a car? Part of it, Hadhazy explained, is that people generally possess more strength than they use on a daily basis.
Our muscles exert the minimum amount of effort necessary to perform a given action — as E. Paul Zehr, a neuroscientist at the University of Victoria, told Hadhazy: “Why use your whole muscle mass to lift up a cup of coffee?” — so when an emergency forces you to summon up a seemingly newfound level of strength, you’re actually tapping into reserves that already exist.
That being said, though, people showing superhuman strength aren’t actually lifting as much weight as they seem to be:
"Most reported hysterical strength examples describe a person lifting a portion of a vehicle several inches off the ground, and not an entire automobile. There’s the catch: three of the vehicle’s wheels – or maybe even all four, depending on the suspension – remain on the ground, distributing the total weight of the vehicle. Furthermore, a vehicle’s mass is not apportioned evenly; the heaviest part is the engine block, at the front-centre, not at the periphery where the lifting is taking place.
Put that all together – and not to take away from the courage of those who have put themselves at risk to save others – but someone in the standard hysterical strength scenario is probably lifting more on the order of several hundred pounds, not an Incredible Hulk-esque fewthousand."
Still, several hundred pounds is more than many people could pick up by themselves, and more than many have ever tried.
In his book Extreme Fear: The Science of Your Mind in Danger, author Jeff Wise explained the difference between “absolute strength,” the hypothetical amount of force your body could possibly exert, and “maximal strength,” or the amount we can actually generate if we try.
Most people, he reported, have a maximal strength that’s about 65 percent of their absolute strength. In stressful situations, he wrote, that number can rise as “the brain’s fear centers progressively remove any restraint against performance,” but there’s only so high it can go — certain situations can bring a person closer to their maximal strength, Wise explained, but the ceiling is a hard one.
These explanations likely aren’t the whole picture — there’s a lot about the phenomenon of superhuman strength that scientists don’t know, largely because the situations that inspire it can’t ethically be reproduced in a research setting.
“You can’t really design an experiment to do this in a lab and make people think they’re going to die,” Zehr told Hadhazy.
But absent further study, we do know this much: There’s something satisfying, even comforting, about the idea that heroic acts enable us to blow past the limits of our bodies.
Unfortunately, though, even in the face of something as terrifying as a loved one trapped in a burning garage, those limits remain firmly in place. They’re just different — and more human — than we thought they were.
This article originally appeared on Science of Us © 2016 All Rights reserved. Distributed by Tribune Content Agency.