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These are the user uploaded subtitles that are being translated: {143}{222}NARRATOR: Too often, | we take our bodies for granted, {227}{297}but under pressure, | our bodies can show us {302}{385}how extraordinary they can be. {390}{438}This complex machine grew {443}{524}out of millions of years | of evolution. {529}{591}So intricate, | we're still mystified {596}{686}by many of the things | that go on inside us. {751}{793}A hidden world, {798}{923}but one we can now explore | in 3-D as never before. {928}{971}Most of us don't realize {976}{1072}our bones and muscles | have superhuman power. {1077}{1182}But in a crisis, | we can accelerate fast' {1187}{1278}survive a crunching fall | from the sky, {1283}{1333}lift unimaginable weights, {1338}{1432}and drive ourselves | mile after mile. {1487}{1530}Muscles. {1535}{1580}Thousands of fibers. {1585}{1642}Millions of filaments. {1647}{1724}The microscopic engines | that power us all. {1790}{1833}Ready for action {1838}{1935}when the human body | is pushed to the limit. {2381}{2477}A tornado rips | across the Missouri plains. {2482}{2547}Winds over 1 50 miles per hour {2552}{2640}shred everything | in the twister's path. {2792}{2875}When it smashes a trailer home, {2880}{2971}one man is sucked | into the heart of the storm. {3041}{3101}Spun and shaken horrifically, {3106}{3211}his limp body | drops out of the sky... {3216}{3285}a quarter of a mile away. {3337}{3386}SUTER: | lt was crazy. {3430}{3511}l knew that l wasn't | where l was supposed to be. {3532}{3654}And it took me a minute | to realize what was happening. {3770}{3862}NARRATOR: Matt hasn't broken | a single bone. {3887}{3937}How could that be? {4141}{4211}Scientists estimate | Matt hit the ground {4216}{4298}traveling at least | 30 miles an hour. {4440}{4509}Yet his bones protected | his internal organs {4514}{4561}from being smashed. {4758}{4820}-Matt' the door! | -Got it. {4861}{4968}NARRATOR: Our skeleton | is made up of 206 bones. {5031}{5081}From the largest | in our legs and arms {5086}{5169}to the tiny bones | in our toes and fingers. {5210}{5280}They give us the tough, | flexible frame {5285}{5359}that lets us push and pull | on our world. {5386}{5458}Bone is incredibly strong. {5773}{5874}Pound for pound, | bone is stronger than concrete. {6010}{6064}lt has | a strength-to-weight ratio {6069}{6157}found in no other | natural material on Earth. {6219}{6338}The secret to bone's strength | and lightness lies inside. {6430}{6493}lt is a matrix of hollow cells. {6498}{6556}lts walls are as thin as paper. {6561}{6661}Bone gets its rigidity | from calcium and phosphorous, {6666}{6751}materials found in seashells | and teeth. {6756}{6787}But astonishingly, {6792}{6894}almost half of our bone mass | is soft and alive, {6899}{6966}allowing our bones to bend. {7251}{7288}Every seven years, {7293}{7421}a healthy human body completely | replaces every single bone cell. {7444}{7480}[ Creaking ] {7485}{7579}This renewal keeps our bones | incredibly strong {7584}{7639}and uniquely adaptable. {7661}{7766}The beauty of bone | is that it can change, {7771}{7827}in terms of its patterns, {7832}{7994}depending upon the stress that | it sees in that particular area. {7999}{8092}And there are geometric designs | in the bone {8097}{8224}that prevent the bone | from breaking with torsion, {8229}{8340}with compression, | with different types of loads. {8405}{8461}NARRATOR: | You are your bones, {8466}{8543}and they are as unique | as your fingerprint' {8548}{8637}always adjusting | to suit your needs. {8656}{8756}A runner grows stronger | leg bones than a swim mer. {8783}{8893}And a tennis player has bigger | bones in their racket arm. {9002}{9090}Bone is like no other material | in the world. {9201}{9307}Strong enough to be pushed | to unbelievable limits. {9392}{9473}KELLEY: l didn't see anything. | lt was so black. {9478}{9549}And l thought' | "Oh, God, this is it"' you know? {9554}{9605}lt was really scary. {10230}{10339}When l looked up, | there was just nothing -- {10344}{10451}no walls, no furniture, | no nothing. {10456}{10685}Matt! {10718}{10808}l just went back to the end | of the trailer where he was. {10813}{10889}lt was just all gone. {10894}{10937}So... {10989}{11048}l knew l wasn't | gonna be able to find him. {11097}{11179}NARRATOR: When Matt lands | a quarter of a mile away, {11184}{11292}his bones don't break' | not just because they're strong, {11297}{11363}but because they're flexible. {11368}{11483}His rib cage bends | as much as an inch. {11561}{11702}A thighbone can withstand | almost a ton of stress... {11707}{11760}before snapping. {11876}{11985}One final twist | saves Matt's life, {11990}{12040}something that allows his bones {12045}{12131}to use their natural strength | to the maximum. {12217}{12330}As the storm hits, | it hurls a lamp across the room, {12335}{12397}knocking Matt out cold. {12552}{12621}Matt's body goes | completely limp. {12626}{12701}All his muscles | are totally relaxed. {12875}{12997}This allows his bones to evenly | absorb the shock of landing. {13322}{13406}SUTER: They said | that if l was conscious, {13411}{13554}then it would've probably | hurt me more than what it did. {13657}{13705}They said l was so relaxed, {13710}{13761}that's why l didn't get hurt | as bad. {14002}{14051}lt was fantastic. {14056}{14163}He had blood all over him, | but he wasn't hurt' so... {14168}{14253}Where have you been? | Where have you been? {14321}{14421}NARRATOR: We each have | incredible strength inside, {14426}{14490}far more than we know. {14545}{14669}A normal person can move as much | as this guy... {14674}{14738}but only in a crisis. {14900}{14952}BEvERLEY: | lt's a little steep here. {15024}{15065}Aah! {15193}{15259}NARRATOR: Pinned beneath | a 1,200-pound rock' {15264}{15345}sliding toward a cliff | and certain death, {15350}{15413}a climber finds power | in his muscles {15418}{15486}far beyond normal limits. {15583}{15643}[ Screaming ] {15954}{16034}NARRATOR: The Sandia Mountains | in New Mexico {16039}{16096}test many climbers. {16126}{16224}Their granite faces | are notoriously unstable. {16280}{16336}BEvERLEY: | lt's a little steep here. {16524}{16633}EBERLE: Marc was in front' and | l lost my footing just a little. {16638}{16686}And by instinct to catch myself' {16691}{16750}l reached over | and put my hands on the wall. {16768}{16794}Aah! {16840}{16897}And that's when | all hell broke loose. {16997}{17075}The wall essentially | came off in my hands. {17080}{17102}Sinjin! {17107}{17148}This thing was huge. {17153}{17249}And how it didn't crush him | to death, l don't know, {17254}{17306}but l just watched him. {17311}{17422}And l couldn't believe | he was actually still alive. {17475}{17541}NARRATOR: The rock slab | has trapped Sinjin. {17546}{17627}lt could crush his ribs, | but with his arm muscles, {17632}{17745}he's able to hold it off' | but only just. {17762}{17833}Worse, he's on a sloping ledge. {17838}{17937}He's sliding toward | a high cliff and doom. {18072}{18128}He's stunned and in shock' {18133}{18204}but his body | has gone into overdrive. {18259}{18323}Sinjin's survival | depends on what's locked {18328}{18435}in the muscles of his arms, | chest' and shoulders. {18594}{18707}But how can mere muscles | move something that massive? {18781}{18850}Muscle tissue works | by contracting, {18855}{18948}pulling on bone, | using it like a lever. {19009}{19102}These contractions | occur microscopically. {19176}{19332}Each of Sinjin's muscles has | thousands of individual fibers, {19337}{19421}bundled like wires in a cable. {19450}{19548}As we age, muscles | may get bigger or smaller. {19553}{19650}But we're born with every | muscle fiber we'll ever have. {19655}{19754}Within each fiber | are yet smaller filaments. {19759}{19803}To activate the muscle, {19808}{19910}chemicals trigger neighboring | filaments to ratchet together' {19915}{19986}intermeshing | like locked fingers. {19991}{20117}As they slide past each other' | the whole muscle fiber shortens. {20122}{20234}These contractions drive | all our muscle movement. {20262}{20338}Yet the big surprise | is that most of us {20343}{20451}use only about a third of our | muscle fibers at any one time, {20456}{20524}even when we feel | we exert ourselves. {20529}{20630}lt's the way our muscles | deliver power most efficiently. {20635}{20700}But if Sinjin's | going to stay alive, {20705}{20755}he has to do something different {20760}{20852}and move a rock weighing | more than half a ton. {20977}{21086}He's unleashed | all the power in his muscles. {21191}{21311}Sinjin heaved a boulder | weighing 1,200 pounds, {21316}{21422}1 1 /2 times | the world bench-press record. {21478}{21530}Under normal circumstances, | there's no way {21535}{21628}l would have been able to lift | that rock even a little bit' {21633}{21711}let alone lift it | all the way off of my body. {21728}{21827}Sinjin, don't move. | Don't move! {21918}{21968}Don't move! | You're injured. {21990}{22045}NARRATOR: | Sinjin could do the impossible {22050}{22144}because his brain activated | all the fibers in his muscles {22149}{22195}at the same time. {22200}{22268}The resulting power | was so great' {22273}{22354}he risked ripping muscle | from bone. {22391}{22435}Aah! {22560}{22611}NARRATOR: | But in a flash of instinct' {22616}{22729}Sinjin's brain | made a lifesaving decision, {22734}{22868}triggering every single fiber | in his arm and shoulder muscles. {22897}{23021}Together' they fired | in one violent push. {23026}{23074}EBERLE: Aah! {23079}{23130}[ Grunting ] {23191}{23298}Most people can't consciously | or voluntarily {23303}{23351}make their muscles do that. {23356}{23495}lt usually requires | some unique situation. {23512}{23582}An emergency | is a perfect example {23587}{23680}of a situation where you need | a great amount of force. {23685}{23758}Your body synchronizes | instantaneously, {23763}{23808}and you get this huge burst. {23813}{23870}BEvERLEY: l'm gonna call | for some help, okay? {23875}{23957}NARRATOR: | That power carries a cost. {23962}{24008}l n saving his own life, {24013}{24102}Sinjin severely hurt | his arm muscles. {24107}{24229}With the level of pain that | l was realizing that l was in, {24234}{24294}there was blood everywhere. {24299}{24348}You know, things were ugly. {24386}{24409}Aah! {24414}{24488}BEvERLEY: You're not | going anywhere, all right? {24493}{24555}NARRATOR: | But he survived. {24691}{24775}We carry awe-inspiring strength | in our muscles {24780}{24849}that we can sum mon | when we're pushed to the limits. {24854}{24904}But every day, every hour' {24909}{24995}our bones have to handle | huge forces. {25160}{25260}They take a ham mering | from normal life. {25299}{25417}To survive, the human skeleton | has evolved a material so strong {25422}{25498}that no technology can match it. {25818}{25863}These street gymnasts {25868}{25951}are among the world leaders | at free-running... {26005}{26145}...a sport that tests the body's | flexibility to its limits. {26232}{26293}And it's only possible | because our legs {26298}{26371}have high-performance | shock absorbers. {26442}{26502}Running puts a strain | on our legs {26507}{26565}three times our body weight. {26584}{26644}A jump can put the skeleton {26649}{26749}under stress equal to 1 0 times | body weight. {26856}{26977}But the body has ways | to handle such forces. {27026}{27152}On landing, | leg muscles absorb energy... {27157}{27267}like giant elastic bands, | so we don't simply collapse. {27391}{27466}The real key | to withstanding shock {27471}{27585}is human engineering that modern | technology can't match. {27634}{27700}Our knees. {27705}{27772}The knee bones | are connected by ligaments, {27777}{27852}lengths of fibrous tissue | that crisscross. {27857}{27917}As the joint flexes, | they stretch. {27922}{28022}But ligaments are | twice as tough as nylon rope, {28027}{28132}with a combined breaking strain | of nearly a ton. {28151}{28231}At the joint's core, | between the two bones, {28236}{28293}is a remarkable material. {28376}{28411}Cartilage. {28416}{28472}A mere fraction | of an inch thick' {28477}{28560}it absorbs the impact's | full force. {28565}{28637}Cartilage shapes | the nose and ears {28642}{28701}and is made of collagen. {28706}{28819}But in our joints, cartilage | has remarkable properties. {28882}{29024}A weave of collagen fibers | is surrounded by 80% water. {29029}{29126}On impact' it acts | like a water-filled cushion. {29215}{29277}Knee cartilage is so strong, {29282}{29379}it can bear 7 tons | before it gives way. {29447}{29501}What's more, | on the pad's surface, {29506}{29577}collagen fibers | are uniquely arranged {29582}{29646}to make it almost frictionless. {29651}{29712}The knee bones | roll over one another {29717}{29789}like well-oiled bearings. {30023}{30092}l n a lifetime, | hundreds of millions of shocks {30097}{30233}pass through this tiny area -- | a uniquely durable design. {30328}{30405}The human body | is an amazing machine {30410}{30489}holding hidden power | and flexibility. {30494}{30573}But what happens | when we push bone and muscle {30578}{30629}beyond normal limits? {31084}{31212}You'd think serious injury would | stop an athlete in his tracks. {31366}{31419}l n fact' | our bodies have strength {31424}{31503}to override normal reactions. {31508}{31591}So we can ignore damage | and keep going. {31596}{31647}[ Whistle blows ] {31709}{31748}But we only do this {31753}{31870}by drawing on a very special | series of factors. {31898}{31996}Two rival college football teams | are battling it out. {32044}{32099}PETTYS: lt was the first game | of our season. {32104}{32184}lt was in the third quarter. | l was the outside receiver. {32240}{32282}NARRATOR: | Trailing in the game, {32287}{32389}Cerritos College are fighting | to get back on top. {32439}{32533}The play will have | Ryan Pettys receive. {32630}{32748}PETTYS: l caught what is called | an out route, inside upfield. {33139}{33215}l thought l had | gotten shot in the arm {33220}{33267}and it had gotten blown off. {33272}{33336}l thought it was | something very serious. {33341}{33400}Some of the most pain | l've ever had in my life. {33573}{33690}NARRATOR: Running full speed, | two defenders take Ryan down. {33726}{33832}lt's as if a truck hit him | going 20 miles an hour. {33930}{34054}The impact pulls Ryan's | ligaments like rubber bands, {34059}{34167}causing his right shoulder | to separate from his collarbone. {34215}{34286}l m mediately, | thousands of pain sensors {34291}{34333}in the ligaments and muscles {34338}{34441}fire signals to his brain | telling him of the injury. {34462}{34560}At this point' most of us | would collapse in agony. {34565}{34638}But Ryan has no intention | of quitting... {34643}{34718}[ Cheers and applause ] {34723}{34832}...and shuts out the waves | of pain from his shoulder. {34864}{34910}PETTYS: l played | for the rest of the game, {34915}{34964}which would be | about a quarter and a half. {34969}{35017}lt was bad -- | not anything as bad {35022}{35089}as what l experienced the | next couple days through pain, {35094}{35167}because of the adrenaline l had | pumping, but it was bad. {35201}{35302}NARRATOR: Ryan was running | on more than adrenaline. {35365}{35493}Deep in his head, training | helped rewire his brain. {35498}{35652}The way Ryan's brain cells now | connect strengthens his resolve. {35657}{35782}Damage to our bodies | causes pain we all sense. {35849}{35924}But we differ | in how we deal with it' {35929}{35989}how much pain we tolerate. {36022}{36100}Where the difference is | is not in pain threshold. {36105}{36145}lt's in pain tolerance. {36150}{36220}lt's how much | will you put up with {36225}{36281}before you say, "That's it. | l quit"? {36286}{36352}Football players have | a higher tolerance. {36357}{36435}Clearly that's a learning | component. {36440}{36475}lf you're brought up and told {36480}{36589}that it's a sign of weakness | to admit that it hurts, {36594}{36649}you won't admit that it hurts. {36677}{36745}NARRATOR: We can rewire | our brains and body {36750}{36857}to become superhuman -- | at a price. {36889}{37003}Ryan's ligaments | eventually tightened back up. {37008}{37125}But his recovery took longer | because he kept playing. {37167}{37288}For Ryan and his team, | that's the price of victory. {37317}{37388}Everybody plays through pain. {37476}{37555}NARRATOR: But sports isn't the | only place where people choose {37560}{37650}to stress their bodies | beyond their limits. {37806}{37871}One of the most beautiful | of the performing arts {37876}{37946}is also one of the most painful. {38171}{38236}MORE: | Because ballet is an art form {38241}{38323}that's meant to look effortless | and painless, {38328}{38373}l don't think we encourage | each other {38378}{38449}to go on about | how painful it is. {38544}{38633}NARRATOR: Dancing on the tips | of the toes is graceful, {38638}{38748}but it compresses dancers' | joints beyond normal limits. {38753}{38829}Amazingly, | the pressure on the toe bones {38834}{38932}amounts to three elephants | stacked on top of each other {38937}{38999}balancing on one leg. {39034}{39116}Pain sensors in the toe joints | trigger signals {39121}{39221}that fire along nerves | in the leg and spinal cord. {39226}{39326}l n seconds, | pain messages flood the brain. {39331}{39421}Most of us would probably faint. {39426}{39515}Studies suggest women feel pain | sooner than men, {39520}{39600}yet have a higher tolerance | for it. {39624}{39713}MORE: You have to keep | mentally strong. {39718}{39789}l don't think you could be | in this job and do what you do. {39794}{39848}You couldn't do | self-inflicted pain, {39853}{39972}which is what ballet is, | and be too delicate. {40011}{40066}NARRATOR: | Professional ballet dancers {40071}{40109}raise their pain tolerance {40114}{40188}with repeated training | and performances. {40258}{40360}MORE: Everybody's got some kind | of small niggle or injury. {40365}{40486}And the show would never go on | if all we ever did was complain. {40558}{40714}NARRATOR: Whether ballet's | elegance or football's violence, {40719}{40819}the mind can stand | tremendous levels of pain. {40882}{40960}Besides unlocking | our body's resilience, {40965}{41071}the mind can also unleash | superhuman speed. {41076}{41129}We instinctively | call on that power {41134}{41245}when the brain spots a hazard | too deadly to confront. {41328}{41382}Rather than face it' {41387}{41489}we push our bodies to the limit | to escape. {41716}{41807}A wildfire blasts through | the Southern California hills {41812}{41852}at terrifying speed. {41935}{41977}Caught in its path, {41982}{42066}a policeman accelerates | faster than a racehorse. {42127}{42279}That lifesaving burst of power | is from inside. {42402}{42449}MAN: | Strong winds have sent flames {42454}{42510}racing up tinder-dry hillsides | today. {42515}{42600}4,000 acres have now burned | in ventura County. {42605}{42643}[ Siren wailing ] {42648}{42723}NARRATOR: Officer Dan Perkins | is trying to reach residents {42728}{42816}trapped by the approaching | forest fire. {42835}{42888}PERKl NS: | lt was pretty hectic. {42893}{42949}There was a lot of fire | and smoke. {42954}{43016}visibility was pretty low. {43042}{43096}l'm on the approach road now. {43101}{43161}l'm gonna try | to get through to them. {43181}{43294}Trees were falling partway | in the roadway on fire. {43299}{43376}You know, fences were on fire. {43392}{43461}The house that they were at | wasn't on fire yet' {43466}{43537}but it was gonna be soon. {43542}{43604}[ Coughing ] {43628}{43733}NARRATOR: As he gets closer' | Dan's body goes on alert. {43738}{43809}The fire could erupt | at any moment. {43814}{43890}Folks, get in your cars | and follow me out! {43895}{43938}Quickly! Quickly! {43971}{44036}They started to go | to their cars. {44041}{44170}And that's when | the fire storm came over. {44256}{44367}lt was 60, 70 feet above me | when it blew over. {44395}{44501}l thought that was it. | l thought that l was gonna die. {44622}{44727}NARRATOR: An exploding fireball | can outpace an Olympic sprinter {44732}{44818}and normally would engulf | Officer Perkins. {44855}{44912}But his heightened state | of alert {44917}{45000}triggers a powerful | biochemical reaction. {45037}{45119}Adrenaline sends his body | into overdrive, {45124}{45219}cutting loose strength | he didn't know he had. {45254}{45386}Adrenaline | is a very neat hormone. {45391}{45427}You focus. {45432}{45523}lt heightens all senses, | from your hearing, your smell, {45528}{45629}your thought processes, | so that you can be very focused {45634}{45706}to get out | of a dangerous situation. {45775}{45828}NARRATOR: | As Dan senses danger' {45833}{45915}the disaster center in his brain | jump-starts his body, {45920}{45988}and he runs for his life. {46137}{46260}That instant response triggers | a series of critical reactions. {46302}{46354}Just above Dan's kidneys, {46359}{46465}glands inject the hormone | adrenaline into his bloodstream. {46500}{46568}The adrenaline boosts | his heart rate. {46573}{46659}Blood now races | to his muscles quickly. {46720}{46830}Adrenaline signals his liver to | flood the body with glucose -- {46835}{46901}blood sugar for fuel. {47029}{47089}But even that won't save him. {47134}{47219}What really kick-starts | Dan's sprint for safety {47224}{47271}is instant energy. {47276}{47323}lt's there, in our muscles, {47328}{47408}stored for just | such emergencies. {47413}{47501}The human body | has a great resource {47506}{47563}in that it stores energy {47568}{47651}in preparation | for emergency situations. {47678}{47758}lt's kind of like | a high-energy battery. {47763}{47809}lt just stores this energy. {47814}{47856}And so, when you need to, {47861}{47936}you have this quick burst | and you utilize that energy. {47941}{47984}lt's called ATP. {48021}{48121}NARRATOR: | ATP, adenosine triphosphate, {48126}{48233}is the energy molecule | that keeps us alive. {48252}{48322}ATP fuels our muscles. {48327}{48417}lt can be made | by burning glucose or fat. {48590}{48678}We store an emergency reserve | of ATP in our muscles, {48683}{48811}available for instant action, | turbocharging us on demand. {48845}{48876}F or a few seconds, {48881}{49009}the energy burst turns Dan | into a skilled sprinter. {49110}{49166}The 1 00-meter sprint -- {49171}{49238}the ultimate test | of human speed. {49491}{49572}The event lasts | less than 1 0 seconds, {49577}{49631}time enough | for a well-trained runner {49636}{49747}to call on a surge | of high-energy ATP. {49971}{50023}For four precious seconds, {50028}{50098}his body accelerates | at the maximum, {50103}{50195}consuming its emergency | ATP supply. {50263}{50354}Now peak performance is done. {50359}{50480}F or the last 40 meters, the | runner is actually slowing down. {50485}{50591}Then, with the race over' | the body can stop. {50670}{50750}Dan's ATP battery | needs to get him out of danger {50755}{50828}and to his car' 60 meters away. {50864}{50944}PERKl NS: l didn't even think | about what l was gonna do, {50949}{50988}where l was gonna go. {50993}{51058}l just turned and ran. {51063}{51133}l don't think l've run faster | in my life. {51628}{51680}NARRATOR: | For a few key seconds, {51685}{51757}Dan has pushed his body | to its limits. {51798}{51884}Just long enough | to keep him alive. {51933}{51966}PERKl NS: | Once l backed out' {51971}{52029}that's when l realized | what just happened. {52034}{52101}l was just shocked. {52106}{52188}And then l realized | l had to go back in. {52303}{52360}NARRATOR: | With the fire storm past' {52365}{52426}Dan returns to rescue | the eight survivors, {52431}{52517}who had huddled | in a swim ming pool. {52522}{52572}By saving his own life, {52577}{52666}Dan Perkins was able to rescue | eight others. {52671}{52748}He was later decorated | for valor. {52877}{52979}The human body can move | with infinite variation, {52984}{53094}all of it powered | by more than 600 muscles. {53176}{53310}But on its own, any one of those | muscles is virtually useless. {53315}{53350}Everything we do {53355}{53455}requires many muscles | working in perfect harmony. {53571}{53699}Simply walking involves | coordinating 200 muscles. {53748}{53830}Steering a car -- 1 00. {53835}{53951}And it takes 70 muscles | just to lift a cup of coffee. {53987}{54055}SCH ROEDER: lt's really | a very simple mechanism {54060}{54130}in that we send nervous impulses {54135}{54200}through the nervous system | to the muscles. {54205}{54272}And if it's all worked together | very tightly {54277}{54347}in a very organized, | synchronized pattern, {54352}{54412}we can perform these skills. {54468}{54503}NARRATOR: | Not all muscles {54508}{54581}have the same number | of controlling nerves. {54586}{54655}The body's biggest muscles, | in our legs, {54660}{54751}take orders from 500 nerves. {54756}{54832}These muscles have | the most pulling power. {54837}{54952}Yet the real magic is not | how we control big muscles, {54957}{55007}but the small ones. {55026}{55094}4,000 nerves control the muscles {55099}{55210}in our body's most complex | and useful instruments -- {55215}{55254}the hands. {55355}{55498}Each hand has 27 bones, | 30 individual muscles, {55503}{55642}and more than 1,000 miles of | nerve fibers and blood vessels. {55755}{55881}Coordinating all this | takes a lot of brainwork. {55909}{56001}Merely controlling our hands | takes almost half {56006}{56087}of the part of our brains | dedicated to movement. {56112}{56188}A set of connections | between brain cells {56193}{56247}governs every action. {56270}{56355}But we aren't born | with these connections. {56360}{56397}We have to learn them. {56402}{56519}We gain and maintain this | strength throughout our lives. {56524}{56622}Amazingly, we're learning | how to unleash this power {56627}{56682}even while sleeping. {56851}{56921}Each time a soccer player | kicks a ball, {56926}{57022}his brain records and stores his | muscles' strength and timing, {57027}{57104}making each successive attempt | easier. {57231}{57347}Soon, without thinking, | signals fly down to the muscles {57352}{57437}at more than | 4,000 inches per second. {57485}{57544}And the move becomes automatic. {57719}{57814}But this training continues | off the field... {57856}{57906}...and overnight. {57976}{58034}Coach always tells us to rest' {58039}{58076}go to sleep early | and everything, {58081}{58152}'cause if we don't sleep, | it will affect us in our game. {58157}{58236}We won't want to play | or anything like that. {58274}{58386}NARRATOR: Sleep brings Marco | more than just rest. {58550}{58592}While Marco sleeps, {58597}{58663}the skills he's been practicing | all day {58668}{58776}are reinforced as connections | are strengthened in his brain. {58795}{58904}F or all of us, the brain's | activity while dreaming {58909}{58986}could be as important | in strengthening our skills {58991}{59049}as what we do while awake. {59066}{59125}ROSEKl N D: We know that | when you go to sleep at night' {59130}{59182}especially during REM sleep, | or dreaming sleep, {59187}{59234}that's when your memories | are consolidated. {59239}{59284}That's when you learn | more things. {59289}{59329}lf you're a soccer player {59334}{59379}or whatever it is | you do athletically, {59384}{59429}those things will be | what you dream about. {59434}{59499}And the more time | you spend on those mentally {59504}{59549}and sending signals | to your body, {59554}{59611}the better you're gonna do | basically learning those, {59616}{59647}even as you sleep. {59684}{59715}NARRATOR: | On average, {59720}{59823}we each spend six years | of our lives dreaming. {59828}{59869}And while we dream, {59874}{59969}we're consolidating | control of our muscles. {60070}{60159}To keep our muscles working | over sustained periods {60164}{60217}requires another strength, {60222}{60310}a strength you'll | hardly believe you have. {60315}{60346}This hidden strength {60351}{60452}can keep you going | for hours of nonstop action. {60485}{60555}Paul Hopfensperger | is trying to swim {60560}{60652}2 1 miles | across the English Channel. {60669}{60850}As part of his training, | he gained 1 6 pounds -- of fat. {60870}{60914}His fat cells have grown, {60919}{61017}thickening Paul's arms, | chest' and belly. {61039}{61146}lt's more athletic | than it sounds -- or looks. {61214}{61310}Our early ancestors | probably looked like this. {61315}{61444}For them, fat was a vital way | of storing energy. {61449}{61540}A competitive swim mer is | very much like ancient man {61545}{61628}in being constantly active | and balancing their food intake {61633}{61690}with a tremendous amount | of physical activity, {61695}{61741}as ancient man hunted for food. {61746}{61818}So if we look at a swim mer' | you'd be surprised to find {61823}{61916}that most of the fuel that | they're using is really fat' {61921}{62004}both fat from the diet | and fat that's stored. {62080}{62147}NARRATOR: As Paul heads | into the frigid water' {62152}{62276}his success will depend on how | he manages his body's reserves. {62281}{62385}To start with, carbohydrates | from Paul's last meal, {62390}{62493}stored in the liver and muscles, | quickly convert to glucose, {62498}{62604}then combine with oxygen | to power him forward. {62729}{62851}Paul's muscles are now burning | 3,000 calories an hour' {62856}{62963}the same number of calories | in three large hamburgers. {63016}{63061}But after three miles, {63066}{63151}the easy-access glucose | is running out. {63156}{63236}Paul's facing a fuel crisis. {63294}{63429}lt's a critical point many | athletes know as "the wall." {63518}{63618}lt's the moment | marathon runners dread. {63682}{63726}SCH ROEDER: | The average person has {63731}{63828}about two to three hours' worth | of energy. {63833}{63886}Once that is depleted, {63891}{63977}then you have what's called | hitting the wall, {63982}{64069}where you just feel | this physical fatigue {64074}{64170}and even this mental anguish | like you're just done. {64175}{64233}You need to stop. {64353}{64446}NARRATOR: The brain detects | low blood-sugar levels, {64451}{64524}making you feel so bad, | you want to quit. {64569}{64614}But to keep going, {64619}{64707}your brain has to trigger | a new fuel source. {64749}{64840}To get it' the body does | something astonishing. {64909}{65039}lt begins to cannibalize itself' | feeding off its own fat. {65104}{65207}F or most of us, fat cells | aren't created or destroyed. {65212}{65248}They just shrink or swell {65253}{65330}according to how much fat | we're carrying. {65347}{65397}When glucose runs low, {65402}{65485}we tap fat cells | for reserve energy. {65563}{65660}But fat takes longer to process | than carbohydrates. {65665}{65791}That supply gap | often stops runners cold. {65899}{65970}The best runners | endure the process so often, {65975}{66068}they're used to managing | the fuel supply changeover. {66122}{66265}That lets them make it | past the wall to the finish. {66383}{66473}But triumph for these guys | is only a quarter of the time {66478}{66550}Paul needs | to meet his challenge. {66705}{66799}Like runners, | he has to switch fuel supplies {66804}{66887}and start consuming his own fat. {66990}{67139}Paul's extra layers add 60,000 | calories to his fuel tank. {67144}{67209}That's 1 0 times | the energy of the glucose {67214}{67321}his liver and muscles used | when he dived in. {67372}{67476}But converting fat to fuel | demands extra oxygen, {67481}{67534}straining his lungs. {67672}{67758}He's sucking in | 20 gallons of air a minute, {67763}{67852}absorbed through tubes | narrower than a human hair {67857}{67912}and across tiny membranes {67917}{68024}whose total surface area | is equal to half a tennis court. {68129}{68205}This burst powers Paul | through 1 2 miles {68210}{68252}during the first 6 hours. {68257}{68356}But that's only halfway | across the Channel. {68455}{68549}To succeed, he'll need to keep | pumping fuel to his muscles {68554}{68609}almost until nightfall. {68723}{68835}The fact is, all our bodies | are engineered like Paul's. {68840}{68938}lt's just that he's tuned his up | through practice. {68979}{69018}Paul's training focused {69023}{69116}on improving | his heart's performance. {69134}{69256}SCH ROEDER: The average person | has a 5-liter cardiac output. {69261}{69299}Well, someone who's trained {69304}{69413}would put out about 35 liters | of blood out of the heart' {69418}{69524}which that much more blood | delivers that much more oxygen. {69529}{69578}You can make | that much more energy {69583}{69642}and continue without fatigue. {69676}{69707}NARRATOR: | Each minute, {69712}{69837}Paul's heart pumps seven times | more blood than our hearts do, {69842}{69930}and he's been doing that | for 1 2 hours. {69935}{70033}lt's propelled him 1 8 miles | across the Channel, {70038}{70151}with the French coast | now just three miles away. {70168}{70297}His swim has cost Paul | over 1 4 pounds of body fat. {70302}{70365}l n a day, | he's used more calories {70370}{70432}than most of us use in a week. {70437}{70474}Yet we're all designed {70479}{70591}to store and expend huge amounts | of energy at this rate. {70676}{70713}Despite fatigue, {70718}{70828}Paul keeps his heart and muscles | going for the final push. {71119}{71265}After 1 4 exhausting hours, | Paul touches land. {71298}{71343}He's made it. {71348}{71396}lt was... {71401}{71447}lt was a bloody experience, | l think. {71452}{71497}[ Laughs ] {71522}{71573}NARRATOR: | Strange to say, {71578}{71681}challenges like this | are within all our grasp, {71686}{71811}all because ancient ancestors | struggling to survive the wild {71816}{71897}stored fat fuel for stamina. {71902}{71961}lt's only one of many ways {71966}{72058}we can push our bodies | to their limits. {72218}{72326}Locked inside us, | a network of muscle and bone {72331}{72427}give us unparalleled | flexibility, {72432}{72481}exquisite coordination, {72486}{72589}and in a crisis, brute force | and the speed to escape. {72605}{72657}When it comes to strength, {72662}{72786}a superhero lives inside | every one of us, {72791}{72840}the human body. 34902