by Graham Averill

How Far Can We Go?

Eight days—that’s how long you can live without water. You can go five weeks or more without food. You can last ten days without sleep.

Throughout the past two centuries, scientists have poked and prodded the human body in order test the limits of these complex machines we inhabit. Some barriers we know, others are still a mystery. Now, a growing number of athletes are concerned with one of the more fundamental barrier of the human body: How far can a human being run?

Ultra athletes are testing the limits of the human body. Some are running 300+ miles without resting, while others are pushing single-day distance records. Meanwhile, ultra races continue to expand in both length and field, pushing “average” runners beyond limits previously thought impossible. Today, more than ever, ultra running is the “wild frontier” of sport, where athletes push themselves further, faster, and longer than any human has ever pushed themselves in the past. In the midst of the expanding race distances and broken records, some sports scientists and runners are starting to wonder about the underlying health effects of long distance running. In the pursuit of these vast distances, are ultra runners doing permanent damage to their bodies?

From the Cubicle to the Couch

Is running itself bad for you? Some doctors believe so. It can destroy your joints and do irreparable damage to your shins, hips, knees, and back. Dr. Sanja Gupta, resident physician for CNN, has even suggested that running could weaken your immune system to the point that you’re more likely to suffer from cancer.

“Dr. Gupta went on the air and said what I was doing was going to kill me,” says ultra runner Sam Thompson. “He said that I had no idea the sort of permanent damage I was doing to myself.”

CNN was airing a story on Thompson, an ultra runner from Mississippi who was at the time, in the middle of an attempt to run 51 marathons in 50 days. If that sounds familiar, ultra running superstar Dean Karnazas did a similar feat this past summer. Thompson just did it first, and with less fanfare. Thompson, a Mississippi native, also ran the entire Appalachian Trail solo in 2003, averaging 37 miles a day. It is these great distances that worry Gupta and many others in the medical field.

Recently, many respected doctors have been speaking out about the potential long term damage running could do to an athlete’s body. Some doctors are concerned with everything from organ failure to increased cancer rates, but most are troubled by the frequency of “cumulative trauma,” when a runner wears down the joints and ligaments in the lower half of his body from the repetitive pounding that running requires.

Every running stride places three times the weight of your body on your foot, ankle, knee and hip joints. According to a study performed by the Rocky Mountains University of Health Professionals, high school cross-country runners experience more injuries than athletes playing any other sport, including football.

If running five miles a day could lead to hip, knee, and ankle injuries, then certainly running 100 miles in a day has to be catastrophic on a runner’s body, right? Surprisingly, it’s not as cut and dry as the math would suggest. It may not be the running that’s causing so many injuries with runners. It may be the desk job, cable TV, and the all you can eat buffets.

According to a 2004 Harvard study, the human body is actually designed for long distance running. In fact, the ability to run great distances was critical to our species’ survival. The study shows humans have elongated tendons which provide spring in our running stride. The same tendons are much shorter in chimps and apes, our evolutionary cousins. Meanwhile, the arches in our feet and the broad surface areas of our joints disperse the shock from impact when running, and our gluteus-maximus, which is much larger than that of our evolutionary ancestors, provides running strength and speed. The biggest edge we have on other species, though, is our ability to sweat through millions of pores in our skin, a unique attribute that allows us to regulate our body temperature while running great distances at high speeds.

“Running is the most primitive form of transportation,” Thompson says. “Just look at history. We used to cover vast distances just to find something to eat.”

A cursory look at history supports the notion that humans are natural distance runners. Before the Spanish brought horses to America, running was an important aspect to Native American culture and a key form of transportation and communication. Running was a revered activity and a tribe’s runners were treated as heroes. The long distance run itself was almost a religious experience. Runners were often celibate and many carried a dried buffalo heart with them during their runs. According to the book Indian Running, Native Americans were legendary runners before and after European settlement. In the 1680’s, the Mesquakie tribe’s messenger runners ran 300 miles to warn outlying Hopi tribes of an impending enemy attack. In 1903, Native American Charlie Talawepi ran 72 miles in 36 hours to deliver a message. Tales of these running feats pervade native American history.

Today, the Tarahumara Indians in the Copper Canyon of Mexico keep that tradition alive. Their culture centers around long, grueling runs through the deep canyons of Northern Mexico. Runners consistently cover ultra distances well into their twilight years, never complaining about runner’s knee, and living free of the heart disease that plagues so many Americans.

Still, the question remains: If the human body has evolved into a long distance running machine, and cultures from the ancient Native Americans to the Tarahumara of today are natural born ultra runners, then why does it hurt so much when I run a 5K? And why are doctors so concerned about the “cumulative trauma” ultra runners and weekend warriors may be putting themselves through?

One explanation is that Americans have simply forgotten how to run. While running long distances was a key to our survival for millions of years, it is no longer a part of our daily lives in America the way it is in places like Kenya or the Copper Canyon, Mexico. In our increasingly comfortable and sedentary culture, where we predominantly walk from the cubicle to the couch, running has become a lost evolutionary art, just like other formerly pertinent skills like trapping or food gathering.

“The problem is our sedentary life,” says Mike Bur, a long-time ultra runner from Maryland. “In the last 200 years, we’ve gotten comfortable and sedentary. We live in the land of plenty. Why run?”

Bur argues that the average man has actually devolved, losing the natural running technique that served our ancestors so well during the previous two million years. Case in point: People naturally walk heel to toe, transferring the weight and impact from the back of the foot to the front of the foot. Most of us carry that same heel-to-toe strike pattern into our running gait. Today, sports scientists have concluded that this heel to toe strike is the cause of the majority of the cumulative trauma injuries many runners endure. By striking our heels against the ground with every step, the impact bypasses our natural shock absorbers (muscles and tendons) and instead is shot directly into our bones and joints. The natural running strike, the one employed by the Tarahumara Indians and most likely our ancestors, is limited to the forefoot and toes.

“I watch people running all the time and I think, damn, that looks painful,” says Christopher Bergland, a long distance world record holder and author of The Athlete’s Way: Sweat and the Biology of Bliss. “I learned very quickly as an ultra runner that you need to stay on your forefoot and toes. When I run, it’s more like a shuffle. It looks like I’m falling forward and catching myself with my toes.”

This simple shift in a runner’s gait can take months to get used to, but it’s something that most ultra runners come to adopt sooner or later, a fact that helps keep the frequency of common running injuries down in the elite field of long distance running.

“If you run ultras, you have to figure out ways to reduce the impact,” Bergland says. “You become robotic in your technique. I was injured more my first two years running shorter distances than I have been since running ultras.”

Running shoe companies have recently begun trying to introduce the notion of the “natural foot strike” to the masses. Nike introduced the Free, designed to minimalize the affect of the running shoe on the runner’s gait, a couple of years ago. More recently, Newton Running Shoe company introduced an entire line of shoes designed to keep a runner’s strike on the forefoot, eliminating the heel from the process and promoting the body’s natural shock absorption.

It’s ironic that the running shoe companies are making such progressive strides to improve the runner’s form since, by many accounts, running shoes are part of the reason we’ve forgotten how to run in the first place.

“A lot of people think running shoes are the reason why so many runners get injured,” says Dr. Scott Murr, an Ironman distance triathlete and sports scientist with Furman University’s Institute of Running and Scientific Training.

In the pursuit to make running easier through technology, shoe companies developed bulky, over-cushioned shoes that have actually led runners away from their natural gait towards the more destructive heel-toe technique.

“I think some of the injuries we see are more of a phenomenon of running shoes than anything else,” Murr says. “I run barefoot twice a week in order to let my body do what it’s naturally supposed to do. There’s a lot of value to running barefoot. It’s the way humans are supposed to run.”

System Failure

Christopher Bergland remembers exactly when he started peeing blood. It was mile 110 during his world record treadmill run in 2004.

“I got off the treadmill to pee and this red sludge came out and hit the side of the toilet,” Bergland says. “It looked like Heinz 57.”

Bergland got back on the treadmill and ran 43 more miles for a total of 153.76 miles. The feat earned him the Guiness World Record for distance run on a treadmill in 24 hours.

It also almost killed him. The blood in Bergland’s urine was a sign that his kidneys were failing. He was suffering from athletic induced rhabdomyolysis, or renal failure.

“I didn’t even know that sort of thing could happen,” Bergland says. “I thought you could get dehydrated, but that was about it. I didn’t know you could run so far that you could kill yourself.”

After Bergland set the world treadmill record, he was rushed to the hospital, but he still couldn’t fathom the gravity of his situation. “I was feeling cocky, eating a Big Mac. All the doctors were telling me I was on the verge of dying, but it didn’t really register at the time.”

Rhabdomyolysis is a result of muscle protein infecting the kidneys. Your muscles contain a protein called myoglobin that helps the muscles use oxygen. When muscles break down after consistent stress like a long distance run, the myoglobin leaks into the bloodstream and is carried into the kidneys. Once the protein infiltrates the kidneys, the myoglobin can create a toxic reaction, cause a tubular obstruction, or decrease the oxygen supply to the kidneys altogether. Regardless of the process, the end result is the same: kidney failure.

Obviously, Bergland’s case is one of extremes. He was pushing his body further than it had ever been pushed before, going for a world record. But studies show mild cases of rhabdomyolysis are common with endurance athletes. According to a study published in the American Journal of Sports Medicine, most triathletes have unusually high levels of myoglobin in their bloodstream after a competition, even though none of the athletes studied suffered from renal failure. Kidney failure is common enough in ultra circles that runners have a name for it: runner’s rhabdo. Troll the runner’s forums long enough and you’ll come across a number of first person accounts of rhabdo.

In order to treat rhabdo, doctors pump several gallons of water into your body, water your kidneys can’t process, which sits beneath your skin until it is slowly absorbed into your system. If that doesn’t work, it’s on to the dialysis machine, which functions as a substitute kidney.

While kidney failure can lead to death, in Bergland’s case and in the case of most ultra runners, the damage wasn’t permanent. After time, the kidneys begin functioning again. But the fact that runners are beginning to run themselves into the hospital, and potentially to the grave, has raised some concerns. Every year, seemingly healthy people die while running long distance races. Studies show one in every 50,000 marathoners dies suddenly during a race. Many ultra marathon and Ironman triathlon finish lines are occupied with medical tents, where IV fluids flow like bottles of water after a 5K.

Dr. Kenneth Cooper, founder of the aerobics movement during the ‘60s and grandfather of the running boom, now believes running these extreme distances is simply too much for our bodies to handle. Dr. Cooper has recently begun speaking out against running, proposing a theory that suggests extreme exercise like marathons and ultra marathons suppress the immune system, leading to greater rates of cancer later in life. If you’re exercising more than five hours a week at high intensity, Dr. Cooper now says, there’s a possibility you’re doing more harm than good. Other theories propagating the notion that running could be catastrophic pervade the medical industry. One Harvard study suggests anaerobic exercise (short bursts of intensity) reduces the risk of heart disease 100% more than aerobic exercises like distance running. Some doctors are using this study and the occasional case of marathon-induced sudden death to suggest running actually makes you more vulnerable to heart attacks.

Furman’s Dr. Murr says that Cooper and other critics of running aren’t looking at the whole picture.

“Every athlete is different and genetics play a large part in how running will affect our bodies,” Murr says. “Many of these doctors who say running is bad for you aren’t runners themselves, and they’re talking about the overweight masses. Given the obesity problem in this country, most Americans should probably start walking instead of running. But to say running is bad while pointing to one or two cases of heart attacks or kidney failure isn’t fair. Runners simply have to be smart about their training. I would never suggest someone decide over the weekend to run a 50-mile race without having run a 5K, but if a person is consistent and smart with their training, and if they know their family history in regards to heart problems, then I don’t think these distances are as extreme or crazy as people think.”

In fact, studies show that as an athlete’s fitness level improves, the risk of rhabdo declines, suggesting the human body is more adaptable than most of us realize. But to what extent can the body adapt?

Given the proven possibility of kidney failure, the slight risk of sudden death, a potentially weakened immune system, and the growing frailty of the human body, have we realized mankind’s running potential? Dean Karnazes has run 350 miles without sleep. Is that as far as a human will ever run without sleep? The human body may be designed to run long distances, but have we reached the limit of those distances?

The answer, it turns out, may not be in the legs or the kidneys. It may be in the mind.

Mind over Matter

“I stepped up to the starting line and I realized that I simply did not want to be there,” Mike Bur says. “Usually, at the beginning of a 100-mile race, you’re pumped up and looking forward to where this race is going to take you physically and mentally. But I was already exhausted, physically and mentally. I had to convince myself that I wanted to do it. That’s not a great mindset at the beginning of a 100-mile race.”

Bur is talking about the final leg of “The Last Great Race,” which combines six of the better-known 100-mile foot races into one challenge. In order to complete “The Last Great Race,” you have to run all six races essentially back to back, with only three weeks of recovery time between events. Only 28 runners in the world have completed the challenge. Bur is one of the few.

“I’d fly out Thursday night, register for the race on Friday, start running Saturday morning, finish some time on Sunday, catch a red-eye home and be back at work on Monday. Somewhere in there, I ran 100 miles.”

Bur did that six times in under four months, a pace that is virtually unheard of, even in the ultra world.

“Think of it as a battery. You start the first race with 100%. At the second race a few weeks later, you’re 85%. Each time you start a race, you have less of a reserve,” Bur says. “Everything considered, I felt I had done all that I could, mentally, physically, and emotionally. But that was the point. I wanted to take myself there, to that point where I had nothing left.”

It is this same urge that prompted Bergland to run himself into the hospital. The same urge that prompted Sam Thompson to run 51 marathons in 50 days. The same urge that prompted Pam Reed and Dean Karnazes to run 300 and 350 miles (respectively) without sleep. On some level, this is the same urge that pushes your “average” ultra runner to step up to the starting line of a 100-mile race.

“Ultras tear away the layers you have,” Bur says. “It gets you to a very raw point that you can’t get to in our normal, comfortable lives. In a marathon or a 50-miler, you’re not getting to that same raw place. Running 100 miles is like entering a whole other realm.”

There was a time when people spoke the same way about running 26.2 miles. Not too long ago, the marathon was a near-religious experience that defined a person. Now, your average CPA can train for 16 weeks and finish a marathon. Today, the ultra has become the new marathon, with more and more runners itching to try these 50 and 100 mile distances. The Massanutten Mountain Massochist reached its 160-runner limit in under two hours. In order to run the Hardrock 100 in Colorado, you first have to qualify, then you have to enter a lottery because the demand is too high.

Meanwhile, the elite ultra marathoners are pushing the distances further and further. There’s a 200-mile race in Florida called the Wickham Park Marathon. So far, only one person has finished the two-day stage race through the sands and sun of Florida, but every year, people attempt it. There’s a new 200-mile ultra in New England. The time limit is 72 hours. Meanwhile, runners like Karnazes are contemplating a 500-mile continuous run. Or consider the Million Mile Ultra, an ongoing race created by Matt Mahoney to see who can run one million miles in their lifetime.

“Nobody has ever run one million miles and nobody ever will,” Mahoney says. “The leaders right now are on pace to finish in 160 years, and the cutoff is 100 years.”

Regardless of the race’s impossible goals, almost 600 runners have registered for the competition so far. The leader has almost 65,000 miles under her shoes and she’s still running, even though the finish line is nowhere in sight.

“We’re seeing numbers in ultras you didn’t see ten years ago,” Bur says. “It’s human nature, really. ‘If everybody else is doing this distance, let’s see if I can take it up to the next level.’ It’s possible the sport will continue to evolve.”

But how far can runners “evolve”?

“The human body is capable of amazing things,” Sam Thompson says. “You just have to push it. I think it’s definitely possible for someone to run 500 miles in a go. There are a handful of people that could probably do it. But there has to be a line somewhere. You go from pushing your body to limits that are exciting, to just being plain crazy. There’s a gray line out there somewhere that distinguishes the two, I’m just not sure where it is.”

Matt Fitzgerald, author of Brain Training for Runners, says that gray line might be centered in the brain. Fitzgerald is a proponent of the Central Governor Model of fatigue, which in recent years has revolutionized the understanding of the role of the brain in endurance activities. The conventional model of fatigue is muscle centered, focusing on catastrophic events like lactic acid accumulation. You run a certain amount of miles, lactic acid sets in, and you’re done. The VO2 max works on a similar principal, setting a hard limit on an athlete’s performance. Fitzgerald and other believers in the Central Governor Model believe there is more to fatigue than a single catastrophic event.

“We’re learning that fatigue is actually a self protective mechanism led by the brain,” Fitzgerald says. “Running hard for a long time is a stressor. The brain constantly receives signals from the body during exercise. When a signal indicates a red flag, the brain automatically reduces the electrical output to those muscles. You haven’t hit any hard physiological limit, your brain is simply preventing you from exercising yourself to death.”

Fitzgerald says this realization is key during an athlete’s training because it could help a runner understand his limits more fully.

“There’s no such thing as running as hard as you can, only running harder than you’ve ever run before,” Fitzgerald says. “Studies show people run significantly faster when running against another person as opposed to running solo during time trials, even though the runner perceives he is running as hard as he can in both cases.”

According to Fitzgerald, if your brain is convinced from the start that you can keep a certain pace through the finish line, then there’s a higher likelihood that you’ll be able to maintain that pace. He points to the four minute mile barrier as proof of the power of the brain over limits. Before Roger Bannister broke the four minute mile, it was an unbreakable line of human performance. People had been trying to break that barrier for a decade. One day Bannister runs a sub-four minute mile and within 18 months, 16 other runners had also accomplished the feat.

“What changed?” Fitzgerald asks. “Bannister proved it could be done. That’s the only thing that changed. In a very physical way, the brains of the other runners reassessed the perceived limits of the human body.”

As the bar continues to be raised with performance, Fitzgerald says that process of reassessing our limits occurs over and over. In a very real sense, it happens with ultra marathoners time and again.

“The first thing you have to do is wrap your mind around that distance,” Bur says. “You have to understand that a human can actually run 100 miles and still be okay. Then you can begin training for it.”

In his book, Fitzgerald claims both the mind and body have to be adapted to the goal before a runner can achieve success, but he’s careful to state the brain can’t override the limits of the human body.

“There is an absolute human limit that will never change,” Fitzgerald says. “The brain and body are inseparable and the brain is a very physical thing. The Central Governor Model can’t change our limits. It only changes how we understand them.”

As to what those limits are, the hard truth remains to be seen, as do the long term health affects of runners trying to discover those limits. Will someone run 500 miles without sleep? Will ultra runners suffer permanent organ and muscle damage later in life? The honest answer is “it’s too early to tell.”

“Most of us are still guinea pigs,” Dr. Murr says. “What’s going to happen to these runners when they’re 60? We don’t know yet. The running boom didn’t hit until the ‘70s. That was only 30 years ago. To do a proper study takes decades. The next ten or 20 years will be interesting, though. We’ll start to see what the health of these endurance athletes will be when they’re older. Right now, we don’t know.”