The limits of the human endurance performance: is it all in your head?


There are limits to the human endurance. But what role does our brain play in it? As Alex Hutchinson, a Canadian scientist and journalist for renowned American magazines, will tell us in this interview: a big one!

Alex Hutchinson is himself an experienced runner and regularly publishes articles in the well-known endurance magazine Outside (after several years of writing for Runner’s World), where he covers a wide range of topics in the field of endurance sports. In his book Endure, he looks into the limits of human endurance performance and investigates influencing factors. According to Hutchinson, the role which our brain has in this is underestimated, while it is actually able to influence our performance considerably. We wanted to know how…

You write in your book that the limiting factor on our performance is not physical or mechanical, but pyschological. Do you mean by that that mental barriers prevent us from unravelling our full potential?

That’s a fair summary of what I wrote in Endure, but it’s maybe worth clarifying what I mean. To say that the limits are psychological doesn’t mean there are no physical or mechanical constraints and you can just “decide” to do whatever you want! It’s more subtle than that.

Imagine you’re running a 10K race. Is there any point during the race where, if someone pointed a gun at your head, you wouldn’t be able to accelerate? Maybe very close to the finish, but otherwise you’re always pacing yourself. If so, what is the physical or mechanical “limit” that’s holding you back during the first 9.9K? If often feels like you can’t go faster, but that’s because you know from experience that you shouldn’t go too fast early in a 10K or you’ll pay the price. So when you put it that way, I think pretty much everyone would agree that the limits to endurance are in some sense psychological. Who among us can really claim that their race execution was so perfect that they were right at the limit of their sustainable pace for every metre of the race?

Whether our body’s “full potential” really is a lot greater than we know is another tough question, but we’ll get into that below!

What exactly is the process in our brains tricking us into thinking we can’t go faster and how did you find out about this?

Nobody really knows the final answers at this point, but in the 1990s a scientist named Tim Noakes proposed that our brains act as what he called a “central governor” that prevents us from pushing to our true physical limits, presumably to protect us from serious damage. Since then there has been lots of scientific debate over how and why this might happen, and whether it’s really true.

The current theory that I find most convincing is that we’re guided by our subjective perception of effort. All the physiological signals we hear about—core temperature, lactate levels, heart rate, and so on—contribute to our general sense of how much effort it takes to continue. When that effort level gets too high relative to what we think we can sustain to the finish, we slow down. This is why on a hot day, we slow down very early in the race, long before we’re actually overheating: we’re responding not to the actual temperature, but to the perception of effort that is affected by the temperature.

How can we try and counteract this and learn where our actual limits are?

I think the question of “actual limits” will always remain hypothetical. There’s no such thing as the perfect race. So it’s more a question of learning to fight against our brain’s desire to slow down, so that we can get a little bit closer to a goal that we’ll never reach.

To some extent, I think just knowing the role of the brain in setting our apparent limits can help. In the middle of a race, if you feel that you’re slowing down, you might blame this on elevated lactate levels or something. If that’s what you think, then there’s nothing you can do but accept the slowdown, because it’s an unavoidable physical truth. But if you believe that you’re slowing down because the elevated lactate levels are making the race feel harder, then maybe this helps encourage you to keep fighting.

More generally, I think the type of positive mindset exhibited by runners like Eliud Kipchoge can make a difference, helping to alter your perception of effort. There’s been some fascinating research demonstrating this over the last few years.

So, are you saying that we can somehow “battle” the lactic acid?

You can’t use your mind to change your lactate levels. But perhaps you can change how you respond to those lactate levels. The thing to remember is that during a race or workout, we’re almost never running at a true “10 out of 10” effort. It would be physically impossible to run like that all time. Instead, we’re always trying to sustain a lower effort that gradually increases so we only hit 10 at the end of the race.

Maybe you’re at 8 halfway through the race, and then rising lactate levels make it feel more like 8.5. But maybe that subjective assessment of 8.5 is partly because you haven’t done a lot of anaerobic training this season, so it’s an unfamiliar sensation and you’re overreacting to how it feels. If you’re able to mentally reframe that feeling of lactate in the legs, perhaps your subjective assessment of effort goes back down to 8.3, and you’re able to sustain a slightly quicker pace to the finish.

Of course, no one actually calculates these numbers midrace! I’m just trying to illustrate what sort of calculations you’re constantly making, without even being aware of it, when you race.

How big an effect do you think it has on the performance of people if they get rid of those mental limits? For example, how much faster do you think the marathon World record could be in the future?

To be honest, I suspect the potential improvements are biggest for recreational athletes, and smallest for elite world-class athletes. One of the traits that enables an athlete to reach the top is the ability to push through discomfort. That said, I do think that even the best athletes can sometimes reach another level. When Eliud Kipchoge ran his 2:01:39 world record last year, I think that performance was partly enabled by the confidence he got from running 2:00:25 under artificial conditions at the Breaking2 race the year before. It changed his perception of what was possible, freeing him up to be aggressive in the second half of the world-record race.

Although professional sports people have experience in trying to get as close to their limit as possible, they still have to learn and relearn every season. There’s some great data showing pain tolerance increases in elite swimmers over the course of a season, maxing out as they approach their goal race. It takes constant practice to suffer well.

Does it work only for endurance sports or also for others?

As a rule of thumb, I’d say the longer the event, the greater the role of the mind. But there are some great experiments showing that mental factors do a play a role even in short bursts of activity. There was one famous study from the 1960s where researchers snuck up behind their subjects and fired a starter’s pistol in their ear right before they did a maximal lift. The fear boosted their strength by 7 or 8 percent!

We hope that some of the thinks Alex mentioned here will also help you to improve your performance in the future!

 “The difference only is thinking. You think it’s impossible. I think it’s possible.” – Eliud Kipchoge before he ran his World record in Berlin


Photo: Florence Tsui

Alex Hutchinson is a science journalist who specialises in writing about endurance sports for Outside Magazine and other publications, and he is the author of the New York Times bestseller Endure. In his own running career, Alex ran for the Canadian national team as middle-distance and cross-country runner. His best times were 3:42 (1500m), 8:00 (3000m), and 13:52 (5000m). These days, Alex still runs most days and competes occasionally in road and cross-country races.





Edited by: Marion Aebi

Carbohydrate periodisation for improved performance


Periodisation of carbohydrate intake in endurance sports – a possibility to efficiently enhance performance and to burn fat.

Several pieces of a puzzle contribute to your running performance as a whole. When you first start running, progress will come quickly. However, one day you will reach a point when it becomes difficult to set new and efficient stimuli. This does not only apply to competitive sports people. Everybody starts working on particular pieces of the puzzle in order to imporve general performance. Nutrition is one of them. In this contribution, sports and nutrition scientist Dr. sc. Nat. Joëlle Flück explains the influence of carbohydrate periodisation in endurance sports on performance and fat reduction.

Carbohydrates are necessary for maximum performance capacity

In endurance sports especially, competition weight is an evergreen. However, weight loss during competition season, in most cases, is not reasonable. The loss of performance due to lack in energy is too big. Another evergreen is the question of what the ideal nutrition looks like. The selection of different forms of nutrition such as, for example, the «ketogene», «low carb» or «paleo» diets is almost too exhaustive, which makes it difficult to keep the overview and to choose a suitable and sensible way for yourself. There is scientific evidence for the necessity of carbohydrates for maximal capacity under intense or maximal pressure or stress. Thus, a low carb diet during intense competition phases is probably not sensible.

Combining low carb and high carb diet

Sports scientists have engaged extensively with the topic of nutrition for optimal increase in performance. They have, amongst others, looked at the effects of a low-carb-high-fat diet on performance. A lot of studies have shown that, in the short term, this form of nutrition can increase fat burning. However, in the long run, it has shown to be rather unfavourable in terms of performing at the maximum of your capacity and to improve generally. Nevertheless, these exact short-term effects can be used in training in order to maximise endurance performance even more effectively. Scientists came up with the idea of combining the low carb and the high carb diet, using the advantages of both and to apply them the best possible way. This is how the concept of carbohydrate perodisation was introduced.

Results of studies on carbohydrate periodisation

Marquet et al. (2016) conducted a study with two groups of triathletes. One group ate according to the common guidelines for sports nutrition : enough carbohydrates before intense sessions/competitions, in order to improve maximum performance, and enough carbohydrates after interval sessions to support recovery processes. The other group ate according to the principle of carbohydrate periodisation : normal supply of carbohydrates before interval training, followed by a low-carb phase before bed time. The morning after, the second group conducted a low intensity session on empty stomach, while the first group only trained after a breakfast rich in carbohydrates. After having repeated the different patterns over three weeks the group testing the carbohydrate periodisation showed greater improvement in both a cycling test (+12% longer) and a 10km run (3% faster). Furthermore, the fat mass of this group was reduced by 0.8kg. The other group, however, showed no significant increase in performance after three weeks and both body weight and body composition remained unchanged.


This study shows that it is possible to improve performance as well as body composition through optimal combination of alternating phases of low and high supply of carbohydrates. Accurate planning of training, nutrition and recovery, as well as time of implementation, are crucial. It is also recommended not to repeat such low-carb phases too many times a week, as they also drain on body resources. Further, susceptibility of infections or risks of overtraining and overloading increase. Therefore, it would be sensible to talk to a specialist and to professionally tailor individual nutrition to training and competition plans, in order to eventually achieve optimal increase in performance capacity and fat reduction.


Joëlle FlückThis is a contribution by sports and nutrition scientist Dr. sc. nat. Joëlle Flück. She works in the sports medicine in Nottwil, where she coaches athletes of all levels, including high performance athletes. At the same time, she individually conducts studies in the area of sports nutrition and she is the vice president of the Swiss Sports Nutrition Society. Being a former middle distance runner, she has won inumerous medals at Swiss championships. Today, she runs longer distances.

Performance fluctuations


Fluctuations in the performances of athletes can amount to 25% within the course of one day. This is what a study conducted by German and British bio scientists put forward recently.

The phenomenon has been known for a long time and it has already been subject to numerous scientific investigations. There are the “early birds”, the people among us who are at the top of their activation level in the mornings, while others can be put in the category of the “owls”, being active late at night but not at all in the mornings. While the former might already be happily whistling in the shower after their regular morning session, the latter are still facing the challenge of overcoming the seemingly insuperable distance between their bed and the bathroom, from where they will probably return soon after their arrival due to the discouraging sight being presented in form of their reflection in the mirror. However, those different types are not necessarily indicators for the actual state of fitness – the presumed morning grouches may as a whole be in the same shape as the happy early birds, or in an even better one. The only difference is that the two types access their performance capacity at different times of the day.

Early bird or morning grouch?

Not so long ago, the general opinion was that it was possible to shape biorhythm through discipline and a certain accommodation time. That is, theoretically, those who tend to have problems getting up early would only need to force themselves to do it for a while and to get used to it and they would soon happily join the early birds for a pre-breakfast session in the forest. Pretty obviously, this seems to be true for many owls – as strong will can move mountains. However, it has been found more recently that, even if people may force themselves into new routines, this does not change the original pattern of their physical capacity. Or, put differently: Early birds stay early birds and owls remain owls, regardless of discipline, self-control or training.

Genetics decide

The reason: A person’s biorhythm depends on genetic predispositions and it can only to a minimal degree be influenced by external factors. The “circadian rhythm”, the biological clock, is a tiny cluster of cells, situated in the diencephalon. The so called “suprachiasmatic nucleus” (SCN), placed in the hypothalamus, sends signals to the brain and it either encourages organs to work or forces them to rest, depending on the time of day and the organ in question. This process is different from person to person and it seems to be highly fixed for each individual. This makes it possible to determine the ideal time for efficient training and starting times in competitions for each athlete. The widely held assumption that athletes are especially capable of performing at their top level in late afternoons or early evenings is only true for the owl types. For the early birds, the level of their performance capacity falls significantly the later it gets.

For each individual, there are significant performance fluctuations during the course of a day

Study with hockey players

At the beginning of this year, the British biomechanic Elise Facer-Child and the German Roland Brandstaetter from the University of Birmingham published the results of a study conducted in 2014 together with (initially) over 120 top athletes. The scientists first determined the biorhythm of each and every test person. This was done by asking them about their sleeping rhythm as well as the perceived peaks in performance capacity during the day. Secondly, amongst all participants, a group of twenty athletes was chosen as a representative sample, standing, at least statistically, for a “biorhythmic average”. The study, in which the label “top athletes” exclusively comprises hockey players, may seem one-sided at first. However, hockey players are especially suitable subjects for studies in sports science, as the sport unites endurance, maximum strength and also coordination. Of course, samples from other sports would have been interesting to include in this study for purposes of comparison. Furthermore, a group of 20 people can hardly be called representative. Nevertheless, this study from Birmingham has some interesting approaches and certain points may show to be crucial for future research.

Training quality depends a lot on the hour

Differences of up to 26 percent

An interesting knowledge gained from the study is that of a varying behaviour of the activation level of different biorhythmic types. In the study, early birds or medium types reached the top of their physical capacity about six hours after getting up, that is, noon or early afternoon. The owls on the other hand reached their top level a lot later- only after eleven hours of being awake. The latter also showed the biggest fluctuations in performance capacity within a day. The levels could differ up to 26% between low (morning) and high (evening). The early birds and the medium types in comparison only showed differences of eight to ten percent within a day. Hence, early birds and medium types capable of performing more equally at all times of the day than owls. It is striking that the owl types are able to perform up to one fourth higher in the evenings than in the mornings. What can we learn from that? “We need to get away from the conventional day times and pay more attention to the inner rhythm”, Brandstaetter recommends. As Facer-Child adds, it should not be all about the clock on the wall but rather about the clock inside each individual, our “circadian rhythm”. She states that training is one thing, but knowing when one is able to perform the best is another.  This is a finding that might play a crucial role in the quality of training. Because even for the early birds, runs in the morning only make sense as some kind of stimulant or for base training, but not as an efficient key session.

This blog was written in collaboration with Fit for Life, the Swiss magazine for endurance sports.