A hundred miles is a lifetime compressed into one day

Lex Fridman opens with a confession that running has always been hard for him, and that he loves it for that reason. The hardest part, he says, is being left alone with his thoughts for an hour or two: dark thoughts about mortality, self-critical ones about weaknesses and unrealized dreams, and a simply human loneliness. Then there are the stretches when all of that fades and he is left empty of negative thought and full of appreciation for the experience itself. Fitness, in that framing, is a byproduct. The real work is facing himself and running through it.

His guest is Zach Bitter, an ultramarathon runner and coach who has held multiple world records in the 100-mile run. Bitter once covered that distance in 11 hours 19 minutes, a pace most people would not sustain for a fraction of the day, and he was, at the time of the conversation, preparing to run across the United States. Fridman wants to know where the mind goes in an ultra: toward demons, inspiration, or no thoughts at all.

Bitter says the interesting thing about a 100-miler, or any all-day event, is that you get the full spectrum of emotion and mental process, positive, negative, and everything in between. It can feel as if you have lived several lives in a single sitting, a simulation of a long stretch of experience compressed into a short window. Early on, a negative thought is easy to slap down: the training is done, the body still feels fresh. Farther in, fatigue lets self-doubt in. Maybe one more long run was needed. Maybe the taper was too short. Left alone, that spiral runs all the way to *why am I here, this is stupid*, and then to dropping out for another race two weeks later, where the same scene repeats.

So his advice for a first 100-miler is blunt: get it done, even if the last stretch becomes what the ultra community calls a death march. You want the highs, the lows, the start, the finish, and the release of emotion at the line, so the next attempt has a template. Fridman then puts two extremes on the table. David Goggins splits the mind in two, hates the weak version of himself, and yells at it. Sam Harris observes the thought and lets it go, trusting that the moment will pass. Bitter will not pick a winner for the whole population. Extreme methods work for extreme people, he says, and most of us sit in the middle, pulling a kick in the pants from one side and a quiet reassessment from the other. At mile 40 of a race he has trained four months for, the better reply is often a calm inventory: there is no real reason to slow down; give it another mile or two and then reassess.

Fridman admits he reaches the *this is the stupidest thing I have ever done* stage faster than Bitter seems to. Excuses arrive on cue: other work would be more worthy, or he will be better prepared in two weeks, so why not start over. Bitter says the quitting voice comes with an extra disadvantage. It is narrow. It reports how you feel in this moment, not how you feel about the whole process.

In 2019, still his best season at the time of the taping, he began putting more weight on the big picture. A race is usually planned four to six months out. You get fit, you prepare for the specifics of the day, and then race morning makes the event look isolated: twelve hours, or 100 miles, as if it were a single outing. Forty miles into a hundred, scrapping the effort sounds almost reasonable inside the ultra world. It is much harder to say you are scrapping the entire last four months. He started repositioning the low: the head is in a bad place, but with the work already done he is 99 percent of the way to a goal he chose when he still had a level head. Keep a loaded list of *why this one, of a hundred possible lives, still wins*, because that questioning voice will come early, in the middle, or late.

Fridman pushes harder. Once you decide to do a thing, should you never quit, even if later, in the full context of a life, it was not the wisest project. He has quit a few things and still regrets them, because quitting opened a door. It is like a muscle. His mind is good at inventing exits, so he works to leave himself none. Bitter says the pattern is familiar in ultras. Beginners are hard to pull off the course: first 50K, first 50 miles, first 100K, first 100 miles. They do not want the first attempt to be a failure. Later, the landscape of other races appears, someone drops once, and the next time the voice arrives sooner.

If you still want the sport, he says, hold yourself to not quitting. Eventually you get a day when the engine is on and the lows still come, but you push through two or three more of them than you did after the dropout. That is when you look back. Those earlier exits were failures on paper, and also the lessons that showed you where the real threshold was. He will not, though, make never-quit a law for every corner of life. In training there are days you should stop a little before you have to, because the stress that elicits growth has already been applied, and more work only lengthens recovery. Fridman still leans the other way. At any given moment, he argues, you are in more danger of quitting than of being slightly suboptimal, and he is tired of a culture that tells him to relax. He remembers the wrestling room: pushed to the limit, not allowed to leave, and made into a better human.

Bitter's own *why* has evolved. He found the events he loves, runnable 100-milers, and then wanted to know how fast he could cover that distance in a controlled environment: no weather, no elevation, no long waits for crew. That is how you end up on a 400-meter track for 100 miles. He could, he thinks, pick three flat hundreds a year, prepare, race, recover, and repeat. What 2019 also taught him is that the mental energy required to keep chasing that mark fades if you never step away. He took roughly half a year off runnable racing and pointed himself at the San Diego 100, a technical trail race with far more climbing, part of it on the Pacific Crest Trail. He finished in just under 17 hours. On a flat surface he can run 11:19. The environment alone added more than five hours.

He sat in second most of the day and took the lead around mile 91 or 92. The deeper gift showed up afterward. He had learned something about pacing the two halves of a hundred, and once he recovered and pointed back at a flat race, the specific workouts were fun again. Back-to-back 30-mile days on a 400-meter track felt like progress rather than a rerun of last year's homework. Enjoyment in the months before the gun, he argues, is one of the best protections against quitting on the day.

Zoomed out, people overestimate what it takes merely to finish 100 miles. The marathon went through the same shift, from a distance you supposedly could not complete without perfect training to a thing people finish in five hours instead of three. Bitter has spoken with people who have almost run 100 miles off the couch. The body, he says, will tolerate far more than it has been exposed to if it has to. Performance is a different game. Then every variable comes to the table: fueling, hydration, pacing, aid-station transitions, whether a pacer is allowed, where a bottle can be handed off. You still cannot account for all of them. Take care of the big ones, then get into a mental space where an unplanned problem is answered with the next sustainable pace, not a ten-minute rumination. At 100-mile speed you have plenty of time to fixate on a mistake. That is usually the wrong use of the time.

Ultra running is a scatter of islands more than a set of exact distances. Bitter names three events that dominate the modern map: the Western States 100, the most competitive trail hundred in the United States, actually 100.2 miles; Ultra-Trail du Mont-Blanc, now perhaps the most competitive hundred on the planet and closer to 105 miles than 100; and the Comrades Marathon in South Africa, 56 miles on the road and still, in his view, the most competitive ultra of all. Americans grumble if a "100-miler" turns out to be 103. In Europe the route often matters more than the number. Jim Walmsley, Bitter's pick as the best male ultra runner going, is the most versatile athlete up to 100 miles, and even he treats some "records" as belonging to a different event after the trail and the season have changed.

Chasing a world record on a track means sweating details that sound tiny and are not. Pass on the outside. If the same oval also hosts a six-day race, you may spend turns in lane two or three and run extra distance all day. Non-moving time has to be in the plan. When Bitter ran 11:19 he stopped three times, maybe three or four minutes in total. The record he was chasing sat at 11:28. Pace for 11:27:30, forget the bathroom, and you can run the splits you wrote down and still miss. It took him almost six years from the day he decided to chase that time. Along the way the goal changed: first break the record, then how fast can I run this, then what would it take for a human to break 11 hours. That barrier, he thinks, is coming, at roughly 6:35 per mile, fast enough to hurt and still slow enough to think.

Lithuania's Aleksandr Sorokin had just taken the record in 11:14:56 or so, about 6:45 per mile against Bitter's 6:47 and a half. Sorokin had also won the 24-hour world championships and the 153-mile Spartathlon. For a hypothetical perfect 10:59, Bitter would want a slight positive or slight negative split; a little fast or a little slow in the first 50 would not change the outcome much. His own second 50 was two minutes faster than the first, and some of his quickest miles came at the end. The oval that day was an awkward 400-plus-38 meters, so he ran the math off that length. Strip out the bathroom laps and the splits were tight. Most races switch direction every four hours: finish the lap you are on, loop around, and go the other way.

Would he like to be the first under 11 hours. He would be lying, he says, if he said no. He is more motivated, though, by seeing it done. Records get broken. If holding one is the reason you live, you need to inspect the rest of your mind, because a 10:50 tomorrow is unlikely to still be the world record in ten years. Each time you break a record you move the sport forward. That was the contribution. Whether you contribute again is beside the point. What he wants is for the performance to pull new people in, people who can make their own mark, so the sport can finally see how fast a controlled 100 miles can be. New shoes, new nutrition, a new generation with advantages the old one lacked: it is easy to sulk that you would have run X with product Y. He would rather not live in that loop. The caveman, he jokes, does not get to claim he would have ruled the world if only he had had a car.

Asked what is most beautiful about running, Bitter offers three timescales. In the moment there is the run that clicks, the endorphins, the so-called runner's high. He and his wife, both competitive ultrarunners, still need rest days, and those days feel as if the morning never started. Non-runners cannot parse that; for them, getting out of a run is the good day. Then there is the medium term: start at this fitness, do these workouts, watch a three-minute interval cover more ground by week four. It is the elementary-school gold star. The star may not mean much. Receiving it still feels great. People love to see improvement.

The cherry on top is the race, the day the work is expressed and judged. Fridman reaches for a frame he also uses in grappling: training is science, competition day is art. He does not want a number so much as a whole performance he can be proud of, taking big risks, refusing to stall, pushing cardio and technique to the edge. Chess has systematic players and players who allow a moment of genius that either pays or does not. That, to him, is art. Bitter likes the frame even when the day goes wrong. An opponent hits a move you were not ready for, or you eat something that costs more time than it returns. Then the enjoyment becomes the drawing board. Mistakes, Fridman says, give us meaning. A day in which you cannot find a flaw would empty the thing out. Bitter looks at his own 11:19 and still sees places to clean up. Sit back and say *that was perfect, let's copy it*, and you will probably run 11:19 again.

Bitter's year-round philosophy is to work first on weaknesses and on qualities that are least specific to race day, then shift toward the specific and the strong as the event nears. Endurance, especially the 100-mile kind, adds a caveat: you want a huge aerobic foundation before you get clever. For him that often means getting very fit at aerobic-threshold pace, what many runners call maximum aerobic function. Short intervals, longer intervals or tempos, and race-pace work nested in long runs are the small puzzle pieces. About 80 percent of the labor sits under them as easy aerobic volume he calls micro-stressing: right up to the threshold, not over it.

Phil Maffetone popularized a still blunter rule: 180 minus your age as the aerobic heart-rate cap. Fridman compares the neatness of it to a physics equation. Bitter treats it as about as good a universal line as you will find, a bell curve whose middle is a decent starting point, not a lab measurement. Check it in the field. If breathing is labored and you cannot finish a sentence, you are probably already above a true aerobic threshold, where you should be able to run for hours and talk. Another governor: breathe in through the nose and out through the mouth. Lose that, and you are going too fast. The advantages are real: you can train a lot of volume with low injury risk, less muscle damage, and more fat metabolism, the direction researchers such as Jeff Volek and Dominic D'Agostino have argued is cleaner for recovery.

Fridman, when fitter, often could not even reach the MAF number. He ran 10 to 20 beats lower, smiled, and liked the pace. Hit the formula and the run became a real workout he could not hold for long. Bitter says the MAF answer would be that the skeletal system cannot yet tolerate the load, or that some sprint work is missing. Come back to 20 miles a week, get comfortable, then inch to 25 and 30. The formula's hidden gift is that it collapses the variables. You are no longer mixing half-right intervals with a half-wrong long run and wondering which one moved the needle. The limit appears when the race lives far outside that zone. A 12-minute event demands practice at race pace: the mechanics, the feel, the judgment. A trail 100 may sit well below MAF. Between a 5K and 100 miles, the target band is enormous.

Ready-made plans, Bitter is honest, always sacrifice individual context. People who want the weeds get one-to-one coaching. The canned versions still follow the same order of operations: eight to twelve weeks of aerobic base, then specifics. He currently offers 5K, half marathon, marathon, 50K, 80 to 100K, and 100-mile plans. The same workouts show up in different places. For a 100-miler, short intervals of 30 seconds to four minutes arrive after the base; their target often comes from a 12-minute time trial. Two minutes on at that intensity, two minutes jog or walk, repeat. If the first two reps are much slower than the last two, the intensity is not dialed. Even splits, then improvement over four to six weeks, is the signal. Level one is four days a week, level two five, level three six with one day off. Do not copy Olympians who wake up and breathe one race four years away, he says, if you work ten hours and have kids. Those constraints are what make coaching non-elites interesting.

Fridman offers himself as a case. After a stretch of stress in Austin he had given himself a pass: carnivore or keto, eat as much as he wanted, whiskey included, and less training. Now he wants grappling competitions in about three months and a run with David Goggins that will be a marathon plus an unknown extra. His constraints are stubborn. He wants to stay carnivore. He likes eating once a day. He feels best running every day, usually the same way, no rest. Bitter does not fight the grain. That combination is a good candidate for MAF, whose trademark is that you never trash yourself so badly that tomorrow is impossible. The key is the starting dose. If an hour a day is a hard rule but 30 minutes at MAF is all the body will take, split the hour: 15 minutes below threshold, 30 at the target, 15 back down, strides at the end if you want them. After four weeks, when the middle 30 is no longer wrecking you, make it 40. The calendar stays intact.

Wear a heart-rate strap early, Bitter says, not as a tyrant but as a translator. On long efforts cardiac drift, dehydration, and heat make the number messy, so he steps away from it more than some coaches do. Fridman's perceived-effort sense is weak; that is exactly the job of the watch. Run, then look. Guess first. After a month or two you can play the game of how close you got. Bodyweight work complicates the picture. Fridman loves push-ups and pull-ups and often does them after the run, sometimes at a heart rate higher than running. Bitter's conclusion: keep the running aerobic. Grappling and the calisthenics already check the high-intensity box. There is no big-picture need to double down on that in the miles.

A marathon and a 100-miler differ most in intensity. MAF feeds the longer race a bit more cleanly. For Fridman, who does not need to be the best possible marathoner or 100-miler, overall time on his feet, plus bodyweight and grappling, is the preparation. The battle will still be physical breakdown, and the mental muscle of doing the slightly unpleasant thing anyway. Bitter's warning is not to make running itself the daily punishment. If every run is misery, you train the association *running equals miserable*, and you will be miserable on the start line. Mix the flavor even when the physiology is the same: one week, one-minute intervals plus threes; the next, a different combo. Put the extra ten push-ups on Tuesday. Put two unwanted sprints on Thursday. Cold showers and hard conversations count. Just do not let the same task stay ugly until you hate the whole process.

People want one answer for what endurance athletes should eat. Bitter will not give it. Endurance is a wide range of intensities, and the individual is the variable most often ignored. Olympic medalists from 3K through the marathon tend to eat moderate-to-high carbohydrate, so the culture concludes that everyone who wants potential at those distances must do the same. Jeff Volek, he notes, works in both health and performance and is one of the main figures at Virta Health, which has reported about a 60 percent success rate helping people reverse type 2 diabetes with a low-carbohydrate protocol. That number is startling against how poorly most diets work at population scale. The difference, Bitter thinks, is coaching: someone to call when you make a mistake instead of throwing the whole thing in the air. That picture, he says, belongs in running too.

The Olympic pipeline may simply be filtering for people who thrive on a carb-heavy training culture. Put the gold medalist on low carb and he probably would not get faster; you already selected him. The more interesting person is the equally talented athlete who got weeded out because the prescribed diet and mileage were unsustainable, or who could eke out a few good years and never become the 38-year-old still on the team. Bitter has eaten what he calls a low-carbohydrate diet for ten years, periodized: some carbohydrate in parts of the season, very low or strict ketogenic in the offseason. He has ranged from mostly plant-based keto to mostly animal-based, rarely more than two weeks of anything 100 percent strict, peaking around 95 percent. The macronutrient profile stayed consistent. Between meat and plants, meat won for him. His highest meat intake was 2019, also his best racing season. He refuses to hand that season to food alone. It also came with two decades of endurance training, and hyper-focusing on one or two variables puts everything else in the least charitable light. The nutritional shift did, he thinks, improve sleep and recovery. A ten-year placebo would be a long placebo.

Clients keep him honest. Some arrive strict keto, raise carbohydrate, and feel better. Some come from a moderate-carb diet, drop it, and nail workouts Bitter expected them to miss. His gut always wants to say they should have responded as he would have. They are not him. Fridman adds his own anomaly: he can go 20 or 24 hours without food and then have a hard two-hour jiu-jitsu session, intellectually sharp and physically fine, which contradicts everything he used to believe about loading carbs three hours out. Self-experimentation is dirty because you cannot rerun the same day the other way, and food is delicious, which makes the science worse. Bitter's line is the one he lives by. We only get one shot at each thing. He does not really care whether a parallel path would have worked just as well.

On 100-mile day, the community agrees on one thing: you want to be very good at burning fat. Intensity is low. If metabolism is skewed hard toward carbohydrate, you have to defend muscle glycogen with a torrent of intake, and that is brutally hard to do for an entire day. Even the leanest endurance athletes carry far more energy in fat than in glycogen. Bitter wants to start the race already burning a high fat share. He may eat some carbohydrate the night before, then lean into the overnight fast, skip breakfast carbs, and take something high-energy and low-volume, such as an SFuels bar built around fat and protein. About 45 minutes in, small amounts of carbohydrate start. At his 100-mile personal-record pace, about nine miles an hour, he is going through roughly 1,000 calories an hour. At that heart rate he figures 80 to 90 percent is fat, 10 to 20 percent carbohydrate. He has raced on as little as 15 grams of carbohydrate an hour and as much as 40. The middle is probably the sweet spot; 40 he can tolerate without gut trouble.

Position papers on single-day ultras still recommend a moderate-carbohydrate diet, and the same papers note that something like 60 percent of participants report a digestion problem during the event. So the question becomes whether you want to flip that coin. Moderate-to-high-carb athletes are often told to take 50 to 70 grams an hour, sometimes as many as 100. What a lab can empty in one hour is not what a stomach will do all day. Gut training is possible, and professionals who burn two or three times resting metabolic rate may have the dietary budget for it. Most people who run ultras are not training much past ten hours a week. For them, 100 grams an hour in workouts is a non-starter if they also want to stay healthy. That game, Bitter says, belongs to a tiny slice of the top one percent.

In training he likes an empty stomach. The biggest sessions are usually in the morning, and whether he eats first depends on whether he needs the calories to train again tomorrow. Show up at noon with zero intake and 5,000 calories still to eat before bed, and the next day suffers. If he lived Fridman's life, he would do almost every run fasted. The test is empirical: if the fasted run is awful and a little food makes both the feel and the progress better, eat. If food makes the workout worse and adds no visible gain, skip it. Peak performance in one narrow activity is not most people's goal. A two percent swing will be drowned by other variables. Fridman treats fasting as a trade he will take even if it costs a bit, because he can put on shoes and not think. Bitter sometimes craves that same small-house, handful-of-foods simplicity. Then he remembers that other people like stuff, and that you should not ostracize yourself out of a life with them.

Fridman names his own controlled chaos: vodka and whiskey, which he does not feel good about the next day, or the day after. Almost everything else in the conversation is optimization. Alcohol, for him, is the symbol of not optimizing, of honoring ancestors and leaving room for the wild thing that happens when you go out with friends. Pay for it for a couple of days, keep a memory for a lifetime, and maybe that is a fair trade. Bitter does not argue. Benefit now, pay later, and sometimes that is the point.

In March 2020 every race vanished. Bitter was putting the finishing touches on a track 100-miler set for mid-to-late April. He could stash the fitness and hope for a fall peak, or spend it. A treadmill was the closest thing to the flat, mechanical running he had been training for. He decided to livestream 100 miles. It became a much bigger production than a man on a belt in his house. The boredom was real, and he still cannot say whether better treadmill-specific prep would have fixed it. The deeper difference from a track was control. On an oval the environment is uniform, but tiny subconscious pace adjustments still belong to you. On a treadmill you answer the belt. You know you are hitting the number. You are also being told what to do, and that gets very frustrating.

He learned on the day that the length of a break almost did not matter. A bathroom stop helped. So did a power hiccup: so much electricity at one end of the house that the treadmill screen blacked out, forcing him to hop to another machine. A handful of seconds off the belt was enough to release the feeling of being commanded, then he could get back on. If he ever did it again, he would want to know how short a reset he actually needs. The irony is that he likes the treadmill for faster work, long intervals and tempos, because then he *wants* to hand the brain the job of holding pace. Those sessions end before the mental fatigue arrives.

One of the guests on that stream was the comedian Bert Kreischer, whom Bitter had met a couple of years earlier and invited almost on a whim. He hoped for five or ten minutes. Kreischer stayed more than an hour, sat through the next guest's slot, and kept talking. Fridman sketches the contradiction: a shirtless party animal with an elegant layer of fat, a lot of post-show drinking, and a sudden love of treadmill miles, including a goal of 2,000 miles that year. Bitter thinks Kreischer is a better athlete than the fat suggests, and that a real race time would yank him a long way from the lifestyle that makes him Bert. His prediction for the 2,000 miles: with 36 hours left in the year, they will find him 100 miles short, and it will be hilarious. Fridman pairs him with Eddie Izzard, getting off the couch to run a marathon a day. For some people the race is the cherry on the training cake. For others the race *is* the cake, taken on without the intricacies, which also reveals something about the human spirit. A switch flips from *that is not possible* to *I am just going to do it*. Kreischer, Bitter suspects, may never even pause at the first thought.

The Transcontinental Run is Bitter's way of getting back the first-time fear that a long ultra career eventually trades for repetition. The classic record route runs from San Francisco to New York. You live out of an RV, run as much as you can by day, sleep, and get up and do it again. That last clause is the whole sport. A single-day ultra lets you wring yourself dry because tomorrow, or next week, you can shut the system down. Here you have to come back for six weeks, if it goes well. Pete Kostelnick's record is a little over 72 miles a day, finished in 42 days, 6 hours, and 30 minutes. Kostelnick had kind weather and one big mistake: he went out too aggressive, had to take a full day off, and so his moving-day average sat closer to 75. Bitter's start date is September 1, the usual window for clearing Sierra passes before big storms and still reaching the East Coast before deep winter.

The hardest work, before a step, is the crew: the RV, the stops, the people who can give that much time. He will document the crossing primarily to raise awareness for Fight for the Forgotten, Justin Wren's charity. If the experience is good he will leave the door open to chase the record, but he does not want the record to become the point two-thirds of the way across the country with a broken leg and the donation button switched off. He is not especially worried about a Forest Gump crowd. There will be remote stretches and some company, not 40 people all the time, unless, Fridman teases, Joe Rogan finds out.

He is not training this as a traditional performance peak. He wants to be injury-proof. Average nine minutes a mile for twelve hours and you have 80 miles, and he will have at least that much moving time, plus walking breaks and stops. Nutrition is the other monster: 10,000 to 15,000 calories a day, a total he has hit only a handful of times in his life, now for six-plus weeks, without destroying the stomach. First step to last might be 13 or 14 hours, then rest, then try not to turn an ankle on an uneven surface among countless footfalls. A few extra pounds of lower-body muscle, a disadvantage on a 6:48 mile, could be an advantage when you never need that pace. The training has become more polarized. He is building two- and three-day simulations of the actual days. One recent week looked wrong on paper: almost 150 miles with two days off. He ran two efforts just over 20 miles, separated by a few hours and a three-mile walk, then got up and ran a bit over 36 in Phoenix in 100-degree heat. Suffer, rest, suffer again.

Veterans tell him the early days decline, bottom out, then slowly improve. He wants the simulations to clear some of that before the start, without adding an extra week of suffering to the trip. The plan is a three-day block of 70 to 80 miles each in early August, then about three weeks for the damage to settle while the adaptation stays. Live video, he learned on the treadmill, is also accountability. Courtney Dauwalter was among some 30 people who had blocked time to appear. Quitting would have meant emails to people who had been gracious. He will show the best, the worst, and the middle. The deeper fuel is the charity. Wren picked wells for a pygmy tribe that local government had long not even counted as human, because women spent entire days walking for water and the community never had surplus time to farm or build. When Bitter hits hour 12 and asks whether he really needs to go out again, he wants the counter-thought: if one of those women woke up and asked whether she really needed to fetch water, the answer would be yes. He does not have to do this. They do. That is the version of never-quit he is willing to live in, because the thing is bigger than he is.

Asked for the greatest endurance athlete of all time, Bitter goes two ways. Haile Gebrselassie, with 27 world records, broke and re-broke marks from the 800 meters at a national level through the marathon, including a 2:03:59 before the carbon-plated shoe era that later studies put at a 2 to 8 percent advantage. Steve Prefontaine is the other pole, less for the times than for the American male runners who still find a catalyst in his story. He could not make varsity football, fell in love with the mile, was told by a college coach that he was a 5K guy, and then popularized that distance in the United States. He raced all guts. One famous line: if you beat him, you would have to bleed to do it. Championship middles often sit and kick. Prefontaine moved early. Leading from the front is usually a bad way to run a personal best. A race, Bitter notes, is often about winning, and Prefontaine thought the front gave him the best chance. He also lived in the amateur era, on food stamps, in a trailer, turning down money so he could stay Olympic-eligible, and he pushed the sport toward a world in which you can sign a contract and still go to the Games. He died in a car accident, having taken fourth in his Olympic 5K, the first man off the podium. Tragedy, Fridman says, is what makes the triumph special. Sunshine and rainbows are a worse movie.

Shoe technology has mattered less in ultras, which still skew toward technical trail, and a lot on roads, tracks, and runnable crushed limestone. Nike's developers found a foam that returned far more energy than the old racing-flat logic had assumed. On force-plate treadmills the gain ranged from 2 to 8 percent depending on gait. Records from 5K through the marathon fell. The women's marathon moved from a 2:16 that had felt untouchable toward 2:14, after 2:18 had been world-class. A carbon plate sits in the foam. Eliud Kipchoge's sub-two project shoe, Bitter believes, never reached the market once rules arrived; the stack was enormous, perhaps with three plates. Prototypes take on the order of 18 months to hit stores, so Nike athletes had them first, and rivals could not wear a competitor's shoe even after release. Kara Goucher, no longer on Nike when the shoe appeared, ran fourth at the Olympic trials marathon, first out, with two of the three qualifiers in the new shoe and a gap inside the performance-advantage range. You can argue, Bitter says, that she was the first person in modern running to lose an Olympic spot to a technological disadvantage. The shoes cost about $250. Two to 8 percent is a huge spread when races are decided by less than a percent. Those questions are still discussable at the level of a shoe. Genetic engineering will be harder. Fridman wonders whether we are near a point where unmodified human performance stops being the pinnacle people watch.

Kipchoge's 1:59:40, with pacers and a prototype, does not settle the official two-hour question. Bitter has no doubt he is world-class, perhaps the best marathoner ever, and thinks he or an equal could go under two with current shoe tech on a very fast course with few tangents. Turns, he notes, are estimated to add about a percent of distance, a quarter-mile over a marathon, which is a decisive margin near a 2:01 certified record. Rules now cap road-shoe stack at 40 millimeters and one carbon plate. Phil Maffetone once estimated a human limit around 1 hour 42 minutes. Ultras, Bitter thinks, will keep falling as the talent pool grows; if the best endurance athletes ever make more money in ultras than in the marathon, the records would go in a couple of years. The marathon's ceiling is murkier. Today's world-record pace is a bit over 4:40 per mile, a 400-meter lap just over 70 seconds, held for 26.2 miles. Go to a track, run one lap as fast as you can, and sit with that. Kipchoge was still smiling at the end. Gymnasts look easy too. Behind that ease sit tens or hundreds of thousands of hours, and in gymnastics one slip can erase four years, or a lifetime, often from a teenager.

The obstacle Bitter is proudest of is not a race. It is the trajectory. He was good enough in high school to make the state meet, then a modest talent at a small Division III college, and he never imagined running as a job. He trained as a teacher, taught about five years at a project-based school just outside Madison, Wisconsin, and loved it. Leaving to chase running was the hardest decision of his life. A co-teacher ribbed him every morning: why are you still here. Failure, at that point, was the more predictable outcome, and that was a blessing. Kids identified as the next NBA star carry a bar that calls them failures if they are not among the best on the planet in ten years. Bitter could have failed quietly and gone back to the classroom, which gave him more freedom to become great because nobody expected it. His advice to young people is to notice the thing they would do with free time even if it never paid, because that may be what gets them out of bed. The internet can turn two or three people in a town into thousands. Look at what you are good at, the thing that sparks, and go, even if it is non-traditional. In special education he saw gifted students for whom the standard path simply did not click, and students who could not read at the usual speed but thrived with a different route. Keep an open mind about the paths forward. That path, Fridman jokes, can land you on a meat-based diet, running across the country, the incredible madman that Bitter is. Fridman will be checking in from September 1. So, he suspects, will Joe Rogan.