When we break past what seem(ed) to be the extent of our physical limits, interesting things happen. Small groups of elite endurance athletes know all about this. When it comes to running, the 42km marathon has become passé in some circles. They now participate in ultra marathons that far exceed the paltry “normal” marathon distance.

This is just one example of new generations of athletes that are pushing themselves beyond what has been previously considered possible. The bodies of members of this elite contingent are forced to adapt in ways as of yet relatively unknown to science.

Long distance endurance events have recently become the topic of much research; teams of scientist want to understand how our bodies can adapt to cope with the extreme challenges presented to our bodies. How can a human run or cycle for 22 hours a day for 12 to 64 days? What happens when they do? The answers will surprise you. Let’s take a look.

Ultra-endurance events take years to train for. To develop the skill and stamina necessary to complete an event, many hundreds, if not thousands, of hours of preparation are necessary. All this exercise, one might think, must be doing great things for these athlete’s health. That is not necessarily the case, however.

On the run

There is a certain point at which exercise can be unhealthy in the long term. People running standard marathons are at slightly higher risk of cardiac arrest. A 2013 University of Hamilton, Ontario study put this figure at almost 1 per 100,000 people running a marathon. It doesn’t sound like a such a big risk, right? Well, those numbers get a lot scarier when we talk about something like an ultra-marathon, and the danger isn’t always during the event itself. Research has begun to show that extreme exercise can have a serious toll on our cardiovascular health. A 2012 Mid-America Heart Foundation study showed that, compared with moderate exercise (which is possibly the greatest thing we can do for our heart) the extreme exercise required to complete long-distance endurance events multiples the risk of cardiac arrest by five. Such athletes are also regularly left with scarring on their heart.

Although hydration is a major risk factor in endurance events, there is a much more dangerous risk associated with over-drinking. The compulsion that an athlete gets to drink more water than necessary when exhausted, causes hyponatremia, a condition that causes salt levels in the bloodstream to become extremely diluted. A 2007 University of Virginia study  discovered that the risk of hyponatremia in endurance athletes far outweighed the risk of dehydration.

There are many changes that may take place in the body to cope with endurance events. Somebody undergoing a multi-day endurance challenge will inevitably burn a huge amount of calories. So much that most people can’t actually eat enough to maintain their body weight. The average daily human calorie consumption is between 1800 and 2500 calories. Ultra-endurance athletes often burn up to four times this amount every day and can struggle to eat half of this amount to maintain their body weight. It becomes inevitable that participants lose a lot of weight by the finish line.

An ultra-marathon runner’s form changes to adapt to the repeated trauma placed on the body. A 2011 University of Lyon study found that our body naturally starts to find ways to displace the downward energy of our mass, to create less impact on landing. This is called the spring-mass system, the distribution of weight in our legs begins acting much like a spring, where the full force of impact is gradual and spread out, making our movements more elastic.

Anybody participating in an extreme endurance event will battle to reduce their weight as much as possible. Less weight means less to carry. An unsettling side of this is that the body starts to adapt in its own way, several studies have shown that ultramarathon running leads to a significant loss of skeletal muscle mass. The body works to get rid of everything unnecessary to the completion of the race.

Another unfortunate side-effect of endurance running is a temporary weakening of the immune system. A 2015 University of Coventry study noted that gastrointestinal problems and inflammation of cells in the immune system were found among 75% of ultramarathon runners who participated in the study.

A sustained risk to the ankle and foot is a significant risk in long distance running. A 2012 University of Ulm study followed 22 athletes on one of the longest ultramarathons in the world. After they had completed the 5000km race from southern Italy to the northern tip of Norway the study participants were each given MRI scans. The scans revealed that their Achilles tendons, the weakest point in the ankle, had widened in diameter. This is one of the many ways our body adapts to the circumstances to reduce the risk of injury.

Aside from changes in the body to adapt to ultramarathons, one curious change that takes place is in the runner’s brain. A 2012 Montpellier University study revealed that during an ultramarathon our brain’s shrink by around 6%. There is no consensus as of yet to explain why. The leading hypothesis according to Dr Schulz, the study lead, is that our brains divert energy from the brain, which is less stimulated during the race, and reorganises the energy elsewhere in the body. The study showed that the athletes’ brains returned to their normal size only after six months.

On your bike

While there are some unique problems associated with endurance running, it appears that cycling, on the other hand, takes less of a toll on our health with perhaps even greater benefits to our body. One of the toughest endurance races in the world, Race Across America, has cyclists racing from coast to coast across 3000 miles of terrain, with a total 50,000 metre incline over a period of 12 days. A 2010 University of Surrey study found that athletes in this race burn on average 6400 calories per day over a distance of 450km. That’s 3-4 times the average human expenditure. The race itself is so tough that less than half of athletes succeed.

The pain associated with long-distance cycling might reward you with more than just Hulk-like thighs. 2011 research conducted by The University of Valencia studied 834 cyclists who had competed in the Tour De France over a 30-year period. The study found that people who completed the race lived on average eight years longer when compared with the average population. 2013 University of Kent research also found that endurance cycling leads to some of the best-known increase in cardiovascular strength.

For men 50 years and older, one downside of long-distance cycling, however, is an increase in a prostate-specific antigen called tPSA. tPSA is strongly linked with prostate cancer. A 2013 Victorian Institute of Sport, Melbourne study of 129 men ranging in age from 50-71 years, in a bike ride of between 55-160km, found that the antigen was increased on average 9.5% post ride, with extra risk appearing in older men and in relation to distance cycled.

It is quite clear that many extreme endurance endeavours are not in the interests of our health. But they do represent something beautiful, way out there at the frontiers of physical human achievement. While us regular humans might think of exercise as something we do for the sake of our health, what’s at stake for these athletes actually may take a toll on their health. Completing such punishing events requires an altogether deeper and more profound motive than physical wellbeing and no doubt they’ll be running their ultramarathons regardless of the scientific findings. There will always be people pushing the boundaries of what is possible – leaving the rest of us to sit back and watch, popcorn in hand, wondering “why”?!


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