"but under pressure, our bodies can show us how extraordinary they can be." "This complex machine grew out of millions of years of evolution." "So intricate, we're still mystified by many of the things that go on inside us." "A hidden world, but one we can now explore in 3-D as never before." "Most of us don't realize our bones and muscles have superhuman power." "But in a crisis, we can accelerate fast' survive a crunching fall from the sky, lift unimaginable weights, and drive ourselves mile after mile." "Muscles." "Thousands of fibers." "Millions of filaments." "The microscopic engines that power us all." "Ready for action when the human body is pushed to the limit." "A tornado rips across the Missouri plains." "Winds over 1 50 miles per hour shred everything in the twister's path." "When it smashes a trailer home, one man is sucked into the heart of the storm." "Spun and shaken horrifically, his limp body drops out of the sky... a quarter of a mile away." "SUTER:" "It was crazy." "I knew that I wasn't where l was supposed to be." "And it took me a minute to realize what was happening." "NARRATOR:" "Matt hasn't broken a single bone." "How could that be?" "Scientists estimate Matt hit the ground traveling at least 30 miles an hour." "Yet his bones protected his internal organs from being smashed." "Matt' the door!" "Got it." "NARRATOR:" "Our skeleton is made up of 206 bones." "From the largest in our legs and arms to the tiny bones in our toes and fingers." "They give us the tough, flexible frame that lets us push and pull on our world." "Bone is incredibly strong." "Pound for pound, bone is stronger than concrete." "It has a strength-to-weight ratio found in no other natural material on Earth." "The secret to bone's strength and lightness lies inside." "It is a matrix of hollow cells." "Its walls are as thin as paper." "Bone gets its rigidity from calcium and phosphorous, materials found in seashells and teeth." "But astonishingly, almost half of our bone mass is soft and alive, allowing our bones to bend." "Every seven years, a healthy human body completely replaces every single bone cell." "[ Creaking ]" "This renewal keeps our bones incredibly strong and uniquely adaptable." "The beauty of bone is that it can change, in terms of its patterns, depending upon the stress that it sees in that particular area." "And there are geometric designs in the bone that prevent the bone from breaking with torsion, with compression, with different types of loads." "NARRATOR:" "You are your bones, and they are as unique as your fingerprint' always adjusting to suit your needs." "A runner grows stronger leg bones than a swim mer." "And a tennis player has bigger bones in their racket arm." "Bone is like no other material in the world." "Strong enough to be pushed to unbelievable limits." "KELLEY:" "I didn't see anything." "It was so black." "And I thought' "Oh, God, this is it"' you know?" "It was really scary." "When I looked up, there was just nothing -- no walls, no furniture, no nothing." "Matt!" "I just went back to the end of the trailer where he was." "It was just all gone." "So... I knew I wasn't gonna be able to find him." "NARRATOR:" "When Matt lands a quarter of a mile away, his bones don't break' not just because they're strong, but because they're flexible." "His rib cage bends as much as an inch." "A thighbone can withstand almost a ton of stress... before snapping." "One final twist saves Matt's life, something that allows his bones to use their natural strength to the maximum." "As the storm hits, it hurls a lamp across the room, knocking Matt out cold." "Matt's body goes completely limp." "All his muscles are totally relaxed." "This allows his bones to evenly absorb the shock of landing." "SUTER:" "They said that if I was conscious, then it would've probably hurt me more than what it did." "They said I was so relaxed, that's why I didn't get hurt as bad." "It was fantastic." "He had blood all over him, but he wasn't hurt' so..." "Where have you been?" "Where have you been?" "NARRATOR:" "We each have incredible strength inside, far more than we know." "A normal person can move as much as this guy... but only in a crisis." "BEvERLEY:" "It's a little steep here." "Aah!" "NARRATOR:" "Pinned beneath a 1,200-pound rock' sliding toward a cliff and certain death, a climber finds power in his muscles far beyond normal limits." "[ Screaming ]" "NARRATOR:" "The Sandia Mountains in New Mexico test many climbers." "Their granite faces are notoriously unstable." "BEvERLEY:" "It's a little steep here." "EBERLE:" "Marc was in front' and I lost my footing just a little." "And by instinct to catch myself' I reached over and put my hands on the wall." "Aah!" "And that's when all hell broke loose." "The wall essentially came off in my hands." "Sinjin!" "This thing was huge." "And how it didn't crush him to death, I don't know, but I just watched him." "And I couldn't believe he was actually still alive." "NARRATOR:" "The rock slab has trapped Sinjin." "It could crush his ribs, but with his arm muscles, he's able to hold it off' but only just." "Worse, he's on a sloping ledge." "He's sliding toward a high cliff and doom." "He's stunned and in shock' but his body has gone into overdrive." "Sinjin's survival depends on what's locked in the muscles of his arms, chest' and shoulders." "But how can mere muscles move something that massive?" "Muscle tissue works by contracting, pulling on bone, using it like a lever." "These contractions occur microscopically." "Each of Sinjin's muscles has thousands of individual fibers, bundled like wires in a cable." "As we age, muscles may get bigger or smaller." "But we're born with every muscle fiber we'll ever have." "Within each fiber are yet smaller filaments." "To activate the muscle, chemicals trigger neighboring filaments to ratchet together' intermeshing like locked fingers." "As they slide past each other' the whole muscle fiber shortens." "These contractions drive all our muscle movement." "Yet the big surprise is that most of us use only about a third of our muscle fibers at any one time, even when we feel we exert ourselves." "It's the way our muscles deliver power most efficiently." "But if Sinjin's going to stay alive, he has to do something different and move a rock weighing more than half a ton." "He's unleashed all the power in his muscles." "Sinjin heaved a boulder weighing 1,200 pounds, 1 1 /2 times the world bench-press record." "Under normal circumstances, there's no way I would have been able to lift that rock even a little bit' let alone lift it all the way off of my body." "Sinjin, don't move." "Don't move!" "Don't move!" "You're injured." "NARRATOR:" "Sinjin could do the impossible because his brain activated all the fibers in his muscles at the same time." "The resulting power was so great' he risked ripping muscle from bone." "Aah!" "NARRATOR:" "But in a flash of instinct'" "Sinjin's brain made a lifesaving decision, triggering every single fiber in his arm and shoulder muscles." "Together' they fired in one violent push." "EBERLE:" "Aah!" "[ Grunting ]" "Most people can't consciously or voluntarily make their muscles do that." "It usually requires some unique situation." "An emergency is a perfect example of a situation where you need a great amount of force." "Your body synchronizes instantaneously, and you get this huge burst." "BEvERLEY:" "I'm gonna call for some help, okay?" "NARRATOR:" "That power carries a cost." "I n saving his own life," "Sinjin severely hurt his arm muscles." "With the level of pain that I was realizing that I was in, there was blood everywhere." "You know, things were ugly." "Aah!" "BEvERLEY:" "You're not going anywhere, all right?" "NARRATOR:" "But he survived." "We carry awe-inspiring strength in our muscles that we can sum mon when we're pushed to the limits." "But every day, every hour' our bones have to handle huge forces." "They take a ham mering from normal life." "To survive, the human skeleton has evolved a material so strong that no technology can match it." "These street gymnasts are among the world leaders at free-running a sport that tests the body's flexibility to its limits." "And it's only possible because our legs have high-performance shock absorbers." "Running puts a strain on our legs three times our body weight." "A jump can put the skeleton under stress equal to 1 0 times body weight." "But the body has ways to handle such forces." "On landing, leg muscles absorb energy... like giant elastic bands, so we don't simply collapse." "The real key to withstanding shock is human engineering that modern technology can't match." "Our knees." "The knee bones are connected by ligaments, lengths of fibrous tissue that crisscross." "As the joint flexes, they stretch." "But ligaments are twice as tough as nylon rope, with a combined breaking strain of nearly a ton." "At the joint's core, between the two bones, is a remarkable material." "Cartilage." "A mere fraction of an inch thick' it absorbs the impact's full force." "Cartilage shapes the nose and ears and is made of collagen." "But in our joints, cartilage has remarkable properties." "A weave of collagen fibers is surrounded by 80% water." "On impact' it acts like a water-filled cushion." "Knee cartilage is so strong, it can bear 7 tons before it gives way." "What's more, on the pad's surface, collagen fibers are uniquely arranged to make it almost frictionless." "The knee bones roll over one another like well-oiled bearings." "I n a lifetime, hundreds of millions of shocks pass through this tiny area -- a uniquely durable design." "The human body is an amazing machine holding hidden power and flexibility." "But what happens when we push bone and muscle beyond normal limits?" "You'd think serious injury would stop an athlete in his tracks." "I n fact' our bodies have strength to override normal reactions." "So we can ignore damage and keep going." "[ Whistle blows ]" "But we only do this by drawing on a very special series of factors." "Two rival college football teams are battling it out." "PETTYS:" "It was the first game of our season." "It was in the third quarter." "I was the outside receiver." "NARRATOR:" "Trailing in the game," "Cerritos College are fighting to get back on top." "The play will have Ryan Pettys receive." "PETTYS:" "I caught what is called an out route, inside upfield." "I thought I had gotten shot in the arm and it had gotten blown off." "I thought it was something very serious." "Some of the most pain I've ever had in my life." "NARRATOR:" "Running full speed, two defenders take Ryan down." "It's as if a truck hit him going 20 miles an hour." "The impact pulls Ryan's ligaments like rubber bands, causing his right shoulder to separate from his collarbone." "I m mediately, thousands of pain sensors in the ligaments and muscles fire signals to his brain telling him of the injury." "At this point' most of us would collapse in agony." "But Ryan has no intention of quitting..." "[ Cheers and applause ] ...and shuts out the waves of pain from his shoulder." "PETTYS:" "I played for the rest of the game, which would be about a quarter and a half." "It was bad -- not anything as bad as what I experienced the next couple days through pain, because of the adrenaline I had pumping, but it was bad." "NARRATOR:" "Ryan was running on more than adrenaline." "Deep in his head, training helped rewire his brain." "The way Ryan's brain cells now connect strengthens his resolve." "Damage to our bodies causes pain we all sense." "But we differ in how we deal with it' how much pain we tolerate." "Where the difference is is not in pain threshold." "It's in pain tolerance." "It's how much will you put up with before you say, "That's it." "I quit"?" "Football players have a higher tolerance." "Clearly that's a learning component." "If you're brought up and told that it's a sign of weakness to admit that it hurts, you won't admit that it hurts." "NARRATOR:" "We can rewire our brains and body to become superhuman -- at a price." "Ryan's ligaments eventually tightened back up." "But his recovery took longer because he kept playing." "For Ryan and his team, that's the price of victory." "Everybody plays through pain." "NARRATOR:" "But sports isn't the only place where people choose to stress their bodies beyond their limits." "One of the most beautiful of the performing arts is also one of the most painful." "MORE:" "Because ballet is an art form that's meant to look effortless and painless, I don't think we encourage each other to go on about how painful it is." "NARRATOR:" "Dancing on the tips of the toes is graceful, but it compresses dancers' joints beyond normal limits." "Amazingly, the pressure on the toe bones amounts to three elephants stacked on top of each other balancing on one leg." "Pain sensors in the toe joints trigger signals that fire along nerves in the leg and spinal cord." "I n seconds, pain messages flood the brain." "Most of us would probably faint." "Studies suggest women feel pain sooner than men, yet have a higher tolerance for it." "MORE:" "You have to keep mentally strong." "I don't think you could be in this job and do what you do." "You couldn't do self-inflicted pain, which is what ballet is, and be too delicate." "NARRATOR:" "Professional ballet dancers raise their pain tolerance with repeated training and performances." "MORE:" "Everybody's got some kind of small niggle or injury." "And the show would never go on if all we ever did was complain." "NARRATOR:" "Whether ballet's elegance or football's violence, the mind can stand tremendous levels of pain." "Besides unlocking our body's resilience, the mind can also unleash superhuman speed." "We instinctively call on that power when the brain spots a hazard too deadly to confront." "Rather than face it' we push our bodies to the limit to escape." "A wildfire blasts through the Southern California hills at terrifying speed." "Caught in its path, a policeman accelerates faster than a racehorse." "That lifesaving burst of power is from inside." "MAN:" "Strong winds have sent flames racing up tinder-dry hillsides today." "4,000 acres have now burned in ventura County." "[ Siren wailing ]" "NARRATOR:" "Officer Dan Perkins is trying to reach residents trapped by the approaching forest fire." "PERKl NS:" "It was pretty hectic." "There was a lot of fire and smoke." "visibility was pretty low." "I'm on the approach road now." "I'm gonna try to get through to them." "Trees were falling partway in the roadway on fire." "You know, fences were on fire." "The house that they were at wasn't on fire yet' but it was gonna be soon." "[ Coughing ]" "NARRATOR:" "As he gets closer' Dan's body goes on alert." "The fire could erupt at any moment." "Folks, get in your cars and follow me out!" "Quickly!" "Quickly!" "They started to go to their cars." "And that's when the fire storm came over." "It was 60, 70 feet above me when it blew over." "I thought that was it." "I thought that I was gonna die." "NARRATOR:" "An exploding fireball can outpace an Olympic sprinter and normally would engulf Officer Perkins." "But his heightened state of alert triggers a powerful biochemical reaction." "Adrenaline sends his body into overdrive, cutting loose strength he didn't know he had." "Adrenaline is a very neat hormone." "You focus." "It heightens all senses, from your hearing, your smell, your thought processes, so that you can be very focused to get out of a dangerous situation." "NARRATOR:" "As Dan senses danger' the disaster center in his brain jump-starts his body, and he runs for his life." "That instant response triggers a series of critical reactions." "Just above Dan's kidneys, glands inject the hormone adrenaline into his bloodstream." "The adrenaline boosts his heart rate." "Blood now races to his muscles quickly." "Adrenaline signals his liver to flood the body with glucose -- blood sugar for fuel." "But even that won't save him." "What really kick-starts Dan's sprint for safety is instant energy." "It's there, in our muscles, stored for just such emergencies." "The human body has a great resource in that it stores energy in preparation for emergency situations." "It's kind of like a high-energy battery." "It just stores this energy." "And so, when you need to, you have this quick burst and you utilize that energy." "It's called ATP." "NARRATOR:" "ATP, adenosine triphosphate, is the energy molecule that keeps us alive." "ATP fuels our muscles." "It can be made by burning glucose or fat." "We store an emergency reserve of ATP in our muscles, available for instant action, turbocharging us on demand." "F or a few seconds, the energy burst turns Dan into a skilled sprinter." "The 1 00-meter sprint -- the ultimate test of human speed." "The event lasts less than 1 0 seconds, time enough for a well-trained runner to call on a surge of high-energy ATP." "For four precious seconds, his body accelerates at the maximum, consuming its emergency ATP supply." "Now peak performance is done." "F or the last 40 meters, the runner is actually slowing down." "Then, with the race over' the body can stop." "Dan's ATP battery needs to get him out of danger and to his car' 60 meters away." "PERKl NS:" "I didn't even think about what I was gonna do, where l was gonna go." "I just turned and ran." "I don't think I've run faster in my life." "NARRATOR:" "For a few key seconds," "Dan has pushed his body to its limits." "Just long enough to keep him alive." "PERKl NS:" "Once I backed out' that's when I realized what just happened." "I was just shocked." "And then I realized I had to go back in." "NARRATOR:" "With the fire storm past'" "Dan returns to rescue the eight survivors, who had huddled in a swim ming pool." "By saving his own life," "Dan Perkins was able to rescue eight others." "He was later decorated for valor." "The human body can move with infinite variation, all of it powered by more than 600 muscles." "But on its own, any one of those muscles is virtually useless." "Everything we do requires many muscles working in perfect harmony." "Simply walking involves coordinating 200 muscles." "Steering a car -- 1 00." "And it takes 70 muscles just to lift a cup of coffee." "SCH ROEDER:" "It's really a very simple mechanism in that we send nervous impulses through the nervous system to the muscles." "And if it's all worked together very tightly in a very organized, synchronized pattern, we can perform these skills." "NARRATOR:" "Not all muscles have the same number of controlling nerves." "The body's biggest muscles, in our legs, take orders from 500 nerves." "These muscles have the most pulling power." "Yet the real magic is not how we control big muscles, but the small ones." "4,000 nerves control the muscles in our body's most complex and useful instruments -- the hands." "Each hand has 27 bones, 30 individual muscles, and more than 1,000 miles of nerve fibers and blood vessels." "Coordinating all this takes a lot of brainwork." "Merely controlling our hands takes almost half of the part of our brains dedicated to movement." "A set of connections between brain cells governs every action." "But we aren't born with these connections." "We have to learn them." "We gain and maintain this strength throughout our lives." "Amazingly, we're learning how to unleash this power even while sleeping." "Each time a soccer player kicks a ball, his brain records and stores his muscles' strength and timing, making each successive attempt easier." "Soon, without thinking, signals fly down to the muscles at more than 4,000 inches per second." "And the move becomes automatic." "But this training continues off the field and overnight." "Coach always tells us to rest' go to sleep early and everything, 'cause if we don't sleep, it will affect us in our game." "We won't want to play or anything like that." "NARRATOR:" "Sleep brings Marco more than just rest." "While Marco sleeps, the skills he's been practicing all day are reinforced as connections are strengthened in his brain." "F or all of us, the brain's activity while dreaming could be as important in strengthening our skills as what we do while awake." "ROSEKl N D:" "We know that when you go to sleep at night' especially during REM sleep, or dreaming sleep, that's when your memories are consolidated." "That's when you learn more things." "If you're a soccer player or whatever it is you do athletically, those things will be what you dream about." "And the more time you spend on those mentally and sending signals to your body, the better you're gonna do basically learning those, even as you sleep." "NARRATOR:" "On average, we each spend six years of our lives dreaming." "And while we dream, we're consolidating control of our muscles." "To keep our muscles working over sustained periods requires another strength, a strength you'll hardly believe you have." "This hidden strength can keep you going for hours of nonstop action." "Paul Hopfensperger is trying to swim 2 1 miles across the English Channel." "As part of his training, he gained 1 6 pounds -- of fat." "His fat cells have grown, thickening Paul's arms, chest' and belly." "It's more athletic than it sounds -- or looks." "Our early ancestors probably looked like this." "For them, fat was a vital way of storing energy." "A competitive swim mer is very much like ancient man in being constantly active and balancing their food intake with a tremendous amount of physical activity, as ancient man hunted for food." "So if we look at a swim mer' you'd be surprised to find that most of the fuel that they're using is really fat' both fat from the diet and fat that's stored." "NARRATOR:" "As Paul heads into the frigid water' his success will depend on how he manages his body's reserves." "To start with, carbohydrates from Paul's last meal, stored in the liver and muscles, quickly convert to glucose, then combine with oxygen to power him forward." "Paul's muscles are now burning 3,000 calories an hour' the same number of calories in three large hamburgers." "But after three miles, the easy-access glucose is running out." "Paul's facing a fuel crisis." "It's a critical point many athletes know as "the wall."" "It's the moment marathon runners dread." "SCH ROEDER:" "The average person has about two to three hours' worth of energy." "Once that is depleted, then you have what's called hitting the wall, where you just feel this physical fatigue and even this mental anguish like you're just done." "You need to stop." "NARRATOR:" "The brain detects low blood-sugar levels, making you feel so bad, you want to quit." "But to keep going, your brain has to trigger a new fuel source." "To get it' the body does something astonishing." "It begins to cannibalize itself' feeding off its own fat." "F or most of us, fat cells aren't created or destroyed." "They just shrink or swell according to how much fat we're carrying." "When glucose runs low, we tap fat cells for reserve energy." "But fat takes longer to process than carbohydrates." "That supply gap often stops runners cold." "The best runners endure the process so often, they're used to managing the fuel supply changeover." "That lets them make it past the wall to the finish." "But triumph for these guys is only a quarter of the time" "Paul needs to meet his challenge." "Like runners, he has to switch fuel supplies and start consuming his own fat." "Paul's extra layers add 60,000 calories to his fuel tank." "That's 1 0 times the energy of the glucose his liver and muscles used when he dived in." "But converting fat to fuel demands extra oxygen, straining his lungs." "He's sucking in 20 gallons of air a minute, absorbed through tubes narrower than a human hair and across tiny membranes whose total surface area is equal to half a tennis court." "This burst powers Paul through 1 2 miles during the first 6 hours." "But that's only halfway across the Channel." "To succeed, he'll need to keep pumping fuel to his muscles almost until nightfall." "The fact is, all our bodies are engineered like Paul's." "It's just that he's tuned his up through practice." "Paul's training focused on improving his heart's performance." "SCH ROEDER:" "The average person has a 5-liter cardiac output." "Well, someone who's trained would put out about 35 liters of blood out of the heart' which that much more blood delivers that much more oxygen." "You can make that much more energy and continue without fatigue." "NARRATOR:" "Each minute," "Paul's heart pumps seven times more blood than our hearts do, and he's been doing that for 1 2 hours." "It's propelled him 1 8 miles across the Channel, with the French coast now just three miles away." "His swim has cost Paul over 1 4 pounds of body fat." "I n a day, he's used more calories than most of us use in a week." "Yet we're all designed to store and expend huge amounts of energy at this rate." "Despite fatigue," "Paul keeps his heart and muscles going for the final push." "After 1 4 exhausting hours, Paul touches land." "He's made it." "It was... lt was a bloody experience, I think." "[ Laughs ]" "NARRATOR:" "Strange to say, challenges like this are within all our grasp, all because ancient ancestors struggling to survive the wild stored fat fuel for stamina." "It's only one of many ways we can push our bodies to their limits." "Locked inside us, a network of muscle and bone give us unparalleled flexibility, exquisite coordination, and in a crisis, brute force and the speed to escape." "When it comes to strength, a superhero lives inside every one of us, the human body."