

Editor's note: This story, on the mystery of superhuman strength, was originally published on July 8, 2019. Watch "The Mountain" Thor Bjornsson, 2018's World's Strongest Man, attempt the world deadlift record of 1,105 pounds at 12 p.m. ET on Saturday, May 2, on ESPN.

HANNAH SMITH WAS a 16-year-old high school basketball player in rural Lebanon, Oregon, when she heard her father scream. She was outside with her younger sister, who was 14 at the time, walking the dogs. The date was April 1, 2013.

Given the date, her first thought was that this was a joke. The sisters walked on. Then there was another scream, desperate, real. They dropped the leashes and ran. Their father was probably 500 feet away, on the other side of a utility shed and workshop, in the vegetable garden portion of their 5-acre property, which sat "in the middle of nowhere." Though not a working farm, the Smith homestead had cows, pigs, chickens, sheds and various large machines for outdoor labor. Their father, Jeff Smith, a millwright at a local factory, particularly enjoyed performing tasks while perched atop his classic 1949 fire-engine-red Ferguson TO-20, an agricultural tractor with enormous rear tires and an exposed engine block, like what's used for hayrides.

On this day, Jeff had been using the rig to pull a tree stump out of the ground. When the Smith girls rounded the corner of the shed, they saw their father's legs sprawling from under the engine block of the Ferguson. Somehow the machine had turned upside down. It did not have a roll cage. Its motor was still running. The weight of the engine block lay across him. The steering wheel pinned his chest to the ground. According to specs listed on TractorData.com, a fully fueled 1949 Ferguson TO-20 weighs approximately 1.4 tons.

ON THE CUSP of battle, members of the Viking warrior cult known as the berserkers stripped down naked. They also chewed on the rims of their iron shields, foamed at the mouth and howled like beasts. They were, now, berserk. Then they hacked their way through opposing armies, killing until there was no one left to kill. For as long as the frenzy lasted, they were "not of human nature," in the words of one Icelandic saga; they were immune to both "fire and iron." The state they entered had a name. It was called berserkergang, and when it finally wore off, the warriors would collapse in total fatigue and sleep for days. (If you wanted to kill a berserker, that, apparently, was the time to do it.)

Not only in war could they summon berserkergang. One evening in the Norse town of Borg, a berserker hero named Skallagrim was playing a friendly "ball-game" -- the sagas give few details about the nature of this sport -- against a team composed of his son and his son's friend, Thord. Frustrated that he was not winning, Skallagrim suddenly went berserk. Whether he also went on to win the match, the saga doesn't say, but he did kill Thord by lifting him in the air and smashing him on the ground, and he would have killed his own son if a bystander hadn't snapped him out of his frenzy.

No one knows if, or to what extent, the berserkers actually existed. Some scholars believe they're rooted in fact. Others assert they're simply figures of legend. But they are part of a deep tradition. The mythologies of countless cultures include stories of altered psychophysiological states in which superhuman deeds become available to the select. Like the related search for fountains of youth, humans have for eons sought the keys that might unlock access to this mysterious matrix of mind and body.

There is anecdotal evidence that humans carry unfathomed reserves of strength. Stories abound of those -- often mothers -- who lift burning cars off trapped children. It raises the question: What would we be capable of if we could access it all?

And so the quest to find the maximal limit of human physical performance has persisted -- in the military, in sports, in science and in pseudoscience. And it has taken many, often quixotic, forms.

The CIA's lunatic studies to create superwarriors were part of the search. Ditto athletes who dose with PEDs. But the quest began long before that.

In 1747, in his lab in Lake Geneva, Swiss scientist Jean Jallabert sent bolts of electricity through the arm muscles of a patient who'd been paralyzed for 15 years. The muscles moved -- violently, strongly -- and the patient, Jallabert reported, eventually recovered the use of his arm. All over Europe, scientists were suddenly conducting batteries of such experiments, electrically stimulating muscles in animals and humans both dead and alive. Especially dead. There was a craze, a fad, of corpse animation, scientists inducing cadavers to sit bolt upright on stages in theaters packed to the rafters with thrilled, gasping audiences -- leading to breakthroughs in our understanding of human neuromuscular mechanics.

Jokichi Takamine, a Japanese chemist and inventor -- the scion of an ancient samurai family -- was among the first to isolate adrenaline, squeezing it from the glands of sheep and oxen, in 1900. His patents on the technique made him as rich as a robber baron. At Harvard, some 20 years later, the scientist Walter Cannon surgically altered the nervous systems of lab cats and dogs, stressed them out, and was thus able to discern that a blast of adrenal hormones in moments of emergency taps into hidden "reservoirs of power" and induces a "violent display of energy." For this crisis response, he coined the phrase "fight or flight."

During the Cold War, the Soviet Union poured money into finding the maximal limits of athletic performance. From the sport-research labs of Moscow came some of the first performance-enhancing drugs. From the same institutions came strength-training techniques still in currency today.

Vladimir Zatsiorsky was a champion competitive Russian acrobat. But while earning a doctorate in biomechanics from the renowned Central Institute of Physical Culture -- where his roommate was powerlifter Viktor Bushuev, future gold medalist at the 1960 Olympics in Rome -- Zatsiorsky found himself hanging around a group of Soviet muscle heads. "They respected one quality in people: strength."

Zatsiorsky went on to become chair of the biomechanics department at the Central Institute, where he would lead the Soviet Union's research into maximal strength. Among other things, he wrote that most people are able to access only 65 percent of their total theoretical muscle potential, while the best weightlifters can approach about 95 percent. He also observed something strange about heart rates. "If you test marathon runners, their highest [heart] rates will be somewhere close to finish line." But the elite Soviet weightlifters Zatsiorsky studied achieved maximal heart rates, in excess of 180 beats per minute, before performing any physical act. They knew how to "bring themselves to this condition, the huge emotional excitement. They don't do anything, no running around. They're just preparing mentally in these extreme ways."

In 1990, Zatsiorsky came to the U.S. and stayed, teaching for 25 years at Penn State. He's now 87 years old and retired in California. His treatise Science and Practice of Strength Training, he said, will soon go into its third edition. Like all the other editions, it will contain a photograph of Zatsiorsky from way back in his Soviet acrobat days. "You will see I have good six-pack."

But one thing Zatsiorsky's work does not contain? The secret to harnessing the outermost reaches of human strength.

At 16, Hannah Smith and her sister faced a life-or-death challenge: Could they find the strength to lift a 1.4-ton tractor off their father? Toni Greaves for ESPN

THE FIRST THING Hannah Smith thought to do was dig. Just the day before, her father had tilled this patch of garden in preparation for planting. The ground, in other words, was soft. Hannah -- all 5 feet, 3 inches and 125 pounds of her -- dropped to her knees beside him and clawed at the earth with her bare hands, screaming at her sister to do the same. Hannah clawed so frantically that only later did she notice that she'd torn some of her fingernails off and that her fingers were covered in blood. "There was no pain," she says.

When she realized that digging wouldn't work, she stood up and looked around. Leaning against the nearby shed were a bunch of two-by-sixes. She took one of them, wedged it under one of the front tires nearest her father's chest and, using two cinder blocks as a fulcrum, tried to lever the tractor off him. The wood bowed under the strain but did not budge the Ferguson. She tossed the lumber aside.

Her father, meanwhile, was struggling to breathe; at one point she thought he'd lost consciousness. Hannah took out her cellphone and dialed 911. "But we're out in the middle of nowhere and it's a 30-minute drive just into town. I knew we didn't have time to wait."

SINCE AUGUST 2006, a term called "hysterical strength" has enjoyed its own Wikipedia entry; its etymology is unclear. The entry, regardless, contains a list of 10 incidents, anecdotal evidence of the phenomenon the term is supposed to describe.

In an Inuit community in northernmost Quebec, near the Arctic Circle, a woman sprints and "tackles" and fights off a polar bear that is predatorily eyeing her 7-year-old son and a friend as the boys, unaware, play hockey, reported the Nunatsiaq News in February 2006.

"There is evidence that humans carry unfathomed reserves of strength. What would we be capable of if we could access it all?"

One night in a parking lot in Tampa in 2011, Danous Estenor, then a 295-pound lineman at the University of South Florida, sees a woman and two men trying and failing to lift a 1990 Cadillac Seville off another person stuck underneath. Estenor takes action. "When I first tried, it didn't budge," he later told a reporter with the St. Petersburg Times. "I backed up. I don't know. But I felt this energy come, and I lifted it."

A year later, in Glen Allen, Virginia, a man is working underneath his BMW in his garage when the jack fails and the car crashes down. His 22-year-old daughter, Lauren Kornacki, home from college, walks into the garage, sees this and takes hold of the car's undercarriage. Like Estenor, she at first fails to lift it. Frustrated, she begins throwing her shoulder against the machine and screaming with such wild abandon that, she says, her little sister, standing nearby, "has a little bit of PTSD from it." The next thing Kornacki recalls is being on top of her father, administering CPR.

E. PAUL ZEHR, a neuroscientist at the University of Victoria, in British Columbia, is something of the go-to expert on the physiology of maximum human physical performance. "What we think are human limits," he says, "are, in fact, just soft barriers." He is familiar with the phenomenon termed hysterical strength, but, he says, "It's not an area that gets research attention." Why? Designing experiments to study it in human beings in the lab would be difficult to achieve, he explains, without also violating the norms of modern scientific ethics.

But those codes weren't always in place. Consider 1961, in Chicago, where a visiting professor of physiology from the University of Tokyo named Michio Ikai teamed up with Arthur H. Steinhaus, an American physiologist and fitness expert with a Ph.D. from the University of Chicago, to run some experiments. They recruited a group of 25 people, hooked them up to a device to measure "maximal efforts to flex the forearm" by pulling on a cable, and asked their subjects to flex as hard as they could; then they walked behind their subjects and, without warning, fired a gun -- a starter's gun! -- next to the subjects' ears. Pow! They asked them to pull the device again. When scared, the subjects overall were 7.4 percent stronger.

"What we think are human limits are, in fact, just soft barriers." E. Paul Zehr

That wasn't all. Ikai and Steinhaus also hypnotized their subjects, assuring them in pacific tones that they were really, really strong. One, two, three, flex: 26.5 percent stronger. Then they handed their subjects Dixie cups with pills inside them -- 30 milligrams of amphetamine sulfate, better known on the street as speed. Swallow, wait for it, woo! Flex: 13.5 percent stronger. Then they got their subjects drunk, or at least buzzed, on grain alcohol. Flex: no improvement. Then they took a big syringe and injected their subjects "intramuscularly" with half a milliliter of adrenaline. How did this make their subjects feel? Who knows? Those details went unrecorded. But the flex numbers were, and the results were surprising: A literal shot of adrenaline produced a statistically insignificant rise in muscle strength.

What did it all add up to? Ikai and Steinhaus thought their findings showed that "psychologic rather than physiologic factors determine the limits of performance." Which is akin to saying they had no idea. Chalking something up to "psychologic" factors is, in science, the equivalent of a shrug.

HANNAH SMITH TOOK hold of one of the small front tires, wrapping her arms around it. Her sister, Haylee, did the same with the other. Then they counted -- one, two, three -- straining to raise the tractor into the air until it felt like the capillaries in the sclera of their eyes had burst. The red Ferguson didn't budge. Their father wheezed, losing air. They tried again, urgent, desperate.

Early spring in Oregon's Willamette Valley can be balmy and fragrant, and so it was on this day. Birds sang, indifferent to the crisis. Sweat ran down from Hannah's face and forehead. She felt lightheaded. Behind her forehead, deep in her temporal lobe, twin nut-sized neuron clusters had by this point shot an electric signal over to her hypothalamus, another neuron cluster, which in turn had activated the adjacent pituitary gland, whose function it is to broadcast a portfolio of hormonal messengers throughout the body's various systems. Hormones triggering hormones, an endocrine cascade. The pituitary signals would almost instantly have reached two yellow blobs of tissue perched atop each of her kidneys like mushroom caps: the adrenal glands. These would then have brewed and spewed more epinephrine and norepinephrine, crucial chemicals and neurotransmitters, than almost assuredly they'd ever produced in Hannah's young life to date.

Among other things, the epinephrine would have flooded her liver, then bound chemically with cells there to help form glucose -- giving her a burst of energy, the stressor equivalent of a sugar high.

Coursing through her bloodstream, the epinephrine would have entered her heart, found the pacemaker cells there and emboldened them to make that muscle beat harder, faster, stronger -- a myocardial turbocharge for the whole of her anatomy.

Hannah and Haylee lifted again ... and this time the tractor moved. It moved maybe an inch in the air and an inch laterally, but it moved. Then they did it again. And again. Up and down, up and down. They were oonching the Ferguson's front end across their father's chest.

Pro strongwoman Liefia Ingalls says that when it's time for extreme lifting, "the thinking goes away." Andrew Hancock for ESPN

IN THE EARLY 1960s, when Jan Todd was a 9-year-old girl growing up in Nova Scotia, she heard a story. A bad accident had left a child trapped underneath a car. The child's mother, apparently unharmed in the crash, had lifted the car and saved her child. The story fired young Jan's imagination. She determined that when she grew up, she too would be strong like this woman who'd performed this heroic feat. And so when she got older she began lifting weights. This was in the early 1970s: not an era when the gyms of America were known for their gender diversity. By the time she was 25, she could dead-lift almost 450 pounds and was profiled in Sports Illustrated as "the world's strongest woman." She eventually broke more than 60 world records.

"The trick of competitive lifting is: Your mind isn't part of the process. You want to be on some strange autopilot," Todd says. "You want to be almost blacked out. On the other hand, if you want to lift something really large, it's sort of like being a Viking berserker. He goes into battle and is some other person during that period of time."

To entertain friends, Todd would bend down and grab hold of the undercarriage of her Ford Fiesta. As she rose into a standing position, up would climb that side of the car.

"The child's mother had lifted the car and saved her child. The story fired young Jan's imagination."

Today Todd is a historian of physical culture at the University of Texas at Austin. When asked about the term "hysterical strength," she says she's never heard that locution before. But she does note that the word "hysterical" comes from the Greek for "womb" and emerged out of a kind of fearful, premodern gynecologic pseudoscience. "There was this concern that your uterus could travel, that it could move upward." It was believed that this propensity made women physically and mentally frail. In his 1615 anatomical tome Mikrokosmographia, a Description of the Body of Man, Helkiah Crooke, the king's physician, wrote of the "hysterical women ... such as are in fits of the mother." Hysterical came to mean a kind of female madness tied to a woman's very anatomy, and "hysterical strength" came to refer to the episodes of physical power that would supposedly come over women afflicted with it. Over time those gendered meanings faded but were never fully erased. Victorian novels are full of men and women -- but mostly women -- who fall into spells of mania, rage and "hysterical strength." The term even found its way into the science fiction of the Cold War, with characters capable of harnessing it at will, weaponizing it. In Joanna Russ' 1975 feminist classic, The Female Man, one of the heroines, an assassin and man hunter living in a dystopian world, does just that: "The room is beginning to sway with the adrenaline I can pump into my bloodstream when I choose; this is called voluntary hysterical strength and it is very, very useful, yes indeed."

According to Todd, it used to be axiomatic that "women could be no stronger than two-thirds of a man. But that was an era when no woman lifted weights." A strength gap still exists, but one woman, a powerlifter, recently squatted 800 pounds, which would've set the men's world record a few generations ago. "At every Olympic Games," Todd says, "it seems like there's always a trainer who will come out and say: 'We're getting close to the limit of human performance; there won't be much record breaking in the future.' But pretty much everything gets broken."

EACH TIME THE Smith sisters lifted the tractor off their father's chest, Hannah could hear him wildly gasping for air. And each time they set it back down they could hear its weight squeeze the air out. Hannah recalls being "super frustrated" by their slow pace, by their failure to remove the machine in one swoop. "I wanted to move it faster," she says. "I wanted to get it up and off of him." She recalls that frustration welling up inside her, fueling bursts of energy, what she calls the "adrenaline pumping."

The girls bent down and hugged the tires and lifted again. It was a kind of positive feedback loop. Feelings of frustration causing energy bursts causing little lifts, which caused more frustration and more energy bursts ... until finally, the tractor came off their father's chest. The girls had moved it about 3 feet. He could finally breathe. His life was no longer in danger. When he was ultimately freed, Jeff stood up and looked at his daughters. "When your mom calls," he said, "don't tell her anything."

Jeff Smith suffered only minor injuries, a broken wrist chief among them. As for Hannah, she collapsed that night in total fatigue. "I did not feel any pain until the next day." She basically couldn't move. She'd strained every muscle in her body from the neck down. She was bedridden for two weeks and never played competitive basketball again.

IN ICELAND, ON a farm in the village of Husafell, a boulder called the Kvíahellan, or the Husafell Stone, has beckoned strongmen for more than 200 years. It is one of the world's most famous tests of strength. These often take the form of boulders, often called "lifting stones" or "strength stones" or, sometimes, "manhood stones." The Husafell Stone reportedly weighs 409 pounds. Legions of confident, burly men have grunted over it and, hours later, dejected, have left it where it lay. No woman had ever gotten it off the ground. Few, if any, had ever tried.

In April, Liefia Ingalls arrived in Husafell from her home in Orange County, California. She is not only a professional competitive strongwoman but a trainer of professional competitive strong people. Just a month before traveling to Iceland, she'd set the world record on monster-dumbbell press at The Arnold, Schwarzenegger's annual extravaganza of strength, for the second time. She'd been planning the Iceland trip for a year with her powerlifting friend Sandra Bradley. "The Husafell is sort of regarded as the archetype of strength," Ingalls says, "and, specifically, male strength."

In some ways, Ingalls says, she prefers stone lifting to other, more technical, strength challenges. She has called herself "overanalytical" and "a highly anxious kind of person." "I'm more of a stoic lifter, a thinking lifter," she says. "But when it comes time to lift stones, that's when I need to tap into all of my energy and all of my power and just be explosive and violent and go. You're talking about maximal capacity. It's just grit. It's just pain tolerance. There's something fatalistic about pushing yourself to the extreme. In that moment, there's nothing else you can do. You can't make a different choice. You can't go back in time and train differently. It's like freedom from analysis. All the thinking goes away. All the worrying goes away. All that matters is that one simple task. Pick up the thing."

The heaviest stone she'd lifted previously was a 340-pound "atlas stone" -- a rock cut into a perfect sphere. The Husafell Stone is shaped like a wedge. It's also dense and smooth and thus difficult to grab and difficult to balance. She wore no gloves. In jeans, a fleece and a green knit cap over shoulder-length hair dyed a shocking pink, she paced around the stone, looking at it, thinking. She squatted down and embraced it. She tried once and failed. She tried again and dropped it. On the third try, she rolled the thing into her lap, stood up ... and walked with it for 30 feet. She felt pride but at the same time frustration. She hadn't carried the stone far enough. "I didn't make it all the way around the pen," she says, which is the traditional Husafell task. "That's going to have to be for later."

Later that day, her friend Sandra also lifted the stone.

As Ingalls learned on this trip, a little-known legend lies behind the Husafell Stone and its origins as a test of strength. The stone sits in a sheep pen adjacent to a 12th-century church. The pastor of this church 200 years ago was also a sheep farmer. He had three sons and four daughters and employed them all on his farm. But he paid his daughters less than his sons. One day, one of the girls challenged this arrangement, agitating for equal wages. Her father replied with a challenge of his own. The wedge-shaped boulder wasn't just a random slab sitting in the yard. The pastor and his sons, all brawny, used it as the pen's gate. When the herd went out to graze, someone lifted the rock out of the way. When the animals came back, back went the 409-pound door. Inefficient, yes, but a good workout. If the daughter could lift the stone and put it back in its place in the gate, well, then she could receive the same wages as her brothers. The father's challenge: Pick up this rock.

Liefia Ingalls finishes the story: "And so she did."