Endurance: beyond the limit

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Everyone knows that being able to deal with fatigue and to keep going even when the effort is extreme, at the very limit of what we can do, is a vital trait in endurance events.

Yet, most athletes don’t truly grasp this idea. Ultimately, everyone “gives up” when they clearly feel their body simply can’t keep going. Mostly, when they reach that point where the desire to continue simply isn’t enough to keep going because the end limit has been reached.  Clearly, this is our perception, but what determines this limit? What mechanism actually makes us “give up”?

What determines this limit

Physiologists focusing on exercise have long grappled with and researched this question.  Until a few years ago, all the reasons that were studied related to the muscles, heart, energy reserves and hydration. Basically, the focus was on those mechanisms that ultimately played a part in the muscles being unable to continue working at the required intensity.  In other words, seeking the limit equated to seeking the causes for the “muscular” limit of performance.

For some time now, though, there has been solid, convincing experimental evidence to show that, when an athlete “gives up” – even when that athlete feels his or her effort has reached the very limit – his or her muscles could actually keep going for a while at the same intensity.

This suggests the limit is really to be found elsewhere, in the athlete’s mind, not muscles. Does this mean all the studies and information about the muscles, heart, energy, hydration and everything else are no longer relevant? Could “everything” be in the mind of the athlete? No, definitely not. Let me be very clear here. All the work done about training, weight, body composition, nutrition and so on remains invaluable. But there is another factor, the mind factor, which has the ability to make us stop making an effort even when our body is still capable of forging on. And this seems to be a normal occurrence.

The psycho-biological model of limit

In essence, the decision whether we “keep going for a little longer” or we “give up” is based on an unconscious assessment by our mind about whether it is worth keeping at it or not. More specifically, it depends on our own personal balance between our perception of the effort (the price we have to pay) and our perception of the importance (for an amateur, I’d happily use the word “beauty”) of the result we are battling towards (the reward for our effort).


When our mind concludes the price has become too high for what we receive in return, it makes us “give up” and this normally happens before the muscles can go no further. This psycho-biological model is based on very convincing experimental evidence, such that, even though it isn’t yet accepted by all scientists in the industry, it will be.



How to move this limit

Should this really be the case, then can we do something – over and above the constant work in training and on nutrition that we have always done – to shift a touch that moment when our mind says “stop”? Definitely, yes. In practice, there are two different paths for working on this: the first is to reduce the perception of effort; the second is to increase the motivation to achieve a sporting result.

Let’s look at this in a little more detail, by analysing the molecular bases for such action. When we exercise for long periods and our energy reserves start dwindling, a substance also increases in our brain: adenosine. This substance can actually influence brain cell activity by binding to specific receptors on the surface of such cells, thus causing a change in how the mind works.

Now, adenosine causes an increased perception of effort for the same intensity of exercise. Plus, adenosinecan also reduce our motivation to try to achieve a specific sporting result. Thus, an increase in adenosine in the brain has negative effects on performance.

How to fight against adenosine

There is nothing certain about how to reduce adenosine production in the brain, but we can act such that, once it has been released outside the cells, this neurotransmitter doesn’t function properly. This can be done by making sure adenosine finds the receptors it is looking for on brain cells already occupied by another substance, making it impossible for the adenosineto act. The substance that can compete with adenosine to bind with such receptors, but without activating them, is caffeine.


As has been widely proven, caffeine improves performance for most athletes. For a long time, work has been done to try and understand why this happens, and today the main – albeit not the only – mechanism at play is that caffeine really inhibits the adenosine activity in the brain.



  • Staiano W, Bosio A, de Morree HM, Rampinini E, Marcora S. The cardinal exercise stopper: muscle fatigue, muscle pain or perception of effort?. Prog Brain Res 2018;240:175
  • Martin K, Meeusen R, Thompson KG, Keegan R, Rattray B. Mental fatigue impairs endurance performance: a physiological explanation. Sports Med 2018;48:2041

A physician and specialist in Food Science and Gastroenterology, he is also an Adjunct Professor at the Postgraduate School of Specialisation in Nutrition Science in the Medical Faculty at Milan State University. He is the Head of the Sport Nutrition Unit at Mapei Sport Service, a sports medicine clinic and research centre in Olgiate Olona, northwest of Milan. He is a nutrition consultant for many professional athletes and teams in a range of sports, including Giro d’Italia and Tour de France winners, teams in the Italian Serie A football league, national athletics champions and a female downhill skiing Olympic gold medallist. He joined Equipe Enervit in 2008.