Endure – Mind, Body and the Curiously Elastic Limits of Human Endurance, by Alex Hutchinson
Reviewed by Marvin Faure
I was delighted to discover this remarkable book. The mental side of endurance has always fascinated me, to the point where a few years ago I did an extensive study into the Motivations of Amateur Cyclists. My objective was to find out why some people are willing to subject themselves for long periods to punishing training regimes, all in order to take part in gruelling endurance events that they have no chance of winning. To many non-athletes their commitment may seem inexplicable, even bizarre (ask your family…).
One of the top motivations (cited by 88% of the 600 people in the study) was “I love the feeling of pushing myself to the limit (and beyond)”. Thus the notion of pushing the limits of human endurance embedded in the Olympic motto Faster, Higher, Stronger, the natural focus of all professional athletes, is also a huge factor for the passionate amateur and the “weekend warrior”.
The limits to human endurance
So what are these limits, and how does one push beyond them? This is a question that Alex Hutchinson has been asking himself for decades. Hutchinson is both an elite distance runner (competing for the Canadian national team, mostly as a miler) and a well-known writer for Outside, the Globe and Mail, and Canadian Running magazine. With a Ph.D. in Physics he has the perfect combination of athletic experience at the highest levels with an inquiring mind and knowledge of how research should be conducted.
He has spent the last decade travelling the world over and speaking to hundreds of scientists, coaches and athletes in his quest to understand the secrets of endurance, and has now written an exceptional book. I cannot recommend Endure too highly to anyone interested in human endurance. It is just as relevant to cyclists as to runners, rowers, swimmers or any other endurance activity.
The book is in three parts: Mind and Muscle, Limits, and Limit Breakers, interspersed with the account of Eliud Kipchoge’s first attempt at running the marathon in less than two hours in 2017.
PART I: MIND AND MUSCLE
Limits are both physical and mental
When we first think about limits to endurance we tend to think of physical limits. These obviously exist: human beings, at least in our current state of evolution, will never be able to run as fast as a cheetah or swim as fast as a shark. Over the past century or so a huge amount of research has been directed at finding ways to build a stronger human “engine” from a physiological point of view (VO2max, lactate threshold and mechanical efficiency). Equally, we cannot ignore the physical limits imposed by the body’s need for fuel and fluids, nor those imposed by extreme temperatures, muscle fatigue or pain.
As all endurance athletes instinctively recognise, however, this picture is incomplete. “It’s all in the head.” “No pain no gain”. “It’s a mental game”. Rule #5. These are all acknowledgements of the importance of developing mental strength alongside physical endurance. In Hutchinson’s expression: “Endurance is the struggle to continue against a mounting desire to stop”. To a considerable extent, therefore, the winner is the person who not only wants it most but is prepared to suffer the most.
The researchers have been catching up, and there is now a substantial and growing body of scientific research showing that indeed, the mind has a significant role to play in determining the limits of human endurance.
Some of the most powerful evidence for this comes in the existence of the “finishing spurt” – the almost-universal ability of athletes to speed up as the finish line approaches. This is true for any endurance event lasting more than about 3 minutes: the final lap of a mile is always significantly faster than the previous lap, as is the final lap or final few hundred metres of any longer event. From a physiological point of view this makes no sense. None of the athletes consciously slow down before speeding up again. Somehow the approaching finish line unlocks a previously-inaccessible reserve of energy.
Similarly, how come the silver medallist is not totally and utterly exhausted and unable to run another step after crossing the finishing line? In a situation where motivation is at its maximum, you would expect the athletes to give everything. And indeed they do… but the fact they can still function and even jog around the track just a few seconds after finishing suggests strongly that they must have had untapped reserves of energy, that somehow they couldn’t access when they needed it most.
More support comes from a fascinating study of over 9 million finishing times at Marathon events around the world: there are large peaks of people finishing just inside significant time cuts (3h, 3h30, 4h…). These data are impossible to explain in purely physical terms. Only the brain can respond to such abstract and arbitrary targets.
Endurance performance thus cannot be explained purely in physical terms. The physiological model needs to be completed by a “psychobiological” model, which essentially says “How hard it feels, and how much you want it, dictates how long you can sustain it”.
In this model, your endurance performance is limited by a decision-making process based on
- Your perception of effort, and
- Your motivation
This makes intuitive sense. If it starts to feel too hard, and there’s no good reason to continue, why would you do so? Conversely, if the effort feels manageable, and you are highly motivated to keep going, why would you stop?
The model tells us that improving your performance, from a mental standpoint, involves either finding ways to reduce your perception of the effort required, or increasing your motivation, or both. As it turns out, it is perfectly possible to do both. Hutchinson brings us back to this in Part III, Limit Breakers, but first he takes us on an in-depth exploration of the physical limits.
PART II: LIMITS
In Part II, Hutchinson devotes a chapter each to six major limits to endurance: pain, muscle, oxygen, heat, thirst and fuel. Although ostensibly physical, there’s a mental aspect to all of these…
Using the cyclist Jens Voigt as an example, Hutchinson shows that well trained endurance athletes can tolerate more pain than ordinary folk. Interestingly, the research shows they perceive pain to the same extent, but they tolerate it for longer. Furthermore, this tolerance depends on their recent training: it varies through the season, and is at its highest after doing significant amounts of high-intensity training (HIT). HIT is thus not only training the body but also the mind.
There’s an obvious question though, if pain limits performance why not take pain killers? Indeed, experiments have shown that taking Tylenol can boost performance by up to 2% in a 10-mile time-trial. Unfortunately, using pain killers preventively may also result in poor pacing (unable to feel the effort, the athletes start out way too fast, for a net-zero result), and also bring a significant risk of accident due to dulled reactions (hence the recent banning of Tramadol in professional cycling).
The IOC Consensus Statement on pain management in elite athletes is clear: “Medications should not be prescribed to athletes for pain or injury prevention” (my emphasis).
The bottom-line on pain: pain tolerance is trainable and leads to better performance. Forget the pills and do your HIT sessions to the max!
In endurance events lasting several hours or more, muscle strength is not the limiting factor. Hutchinson marshals plenty of evidence to show that “at the point of exhaustion in a long endurance challenge, the legs are merely unwilling, not incapable”. Throughout the event one is using only a fraction of one’s available muscle strength. The reserve is there for emergency use, as you would soon find out if threatened by a wild animal, but under normal conditions you can’t access it.
Oxygen is an obvious performance limiter: the reduction in athletic performance with altitude is common knowledge. It is impossible to produce the same power output near the summit of the col du Galibier as in a five minute maximum effort in the valley. Hutchinson notes that a measurable reduction in VO2max has even been found in Canberra (Australia), at only 579m of altitude. In physiological terms, the brain is protecting its own oxygen supply by limiting the availability of oxygen for the muscles. Performance at altitude is of course trainable, which is why alpinists seeking to climb Everest without supplemental oxygen spend weeks acclimatising at altitude, and why professional cyclists do something similar before the Grand Tours.
Hot conditions have a well-documented negative impact on performance and thus represent another limit to endurance performance. It turns out that the body has an in-built safety mechanism: as soon as our internal temperature reaches about 40.0-40.3°C exhaustion sets in and one is forced to stop exercising. We are not all equal: different people’s core temperatures take longer to rise (and they acclimatise more quickly), but we all have roughly the same core temperature limit. Endurance in hot conditions can be prolonged by anything that slows the time it takes for the core temperature to reach the limit: pre-cooling, ice-vests, wet towels, water sprays, drinking crushed ice… Importantly, it can also be prolonged by altering your perception of how hot you are.
Views on drinking during exercise have gone through wild swings in the last century. Until the late ‘60s, endurance athletes were advised to avoid drinking, on the grounds it would slow them down. The advice changed in the early 70’s to drink early and often to “replace all the water lost through sweating… or consume the maximal amount than can be tolerated”. It took the death of a young woman from hyponatremia* at the 2002 Boston Marathon to change the advice again. Current guidelines are much more conservative (“drink when thirsty” – USA Track and Field, quoted by Hutchinson) and tend to emphasise the importance of salt replacement.
Views on dehydration remain controversial, with the oft-quoted figure of 2% claimed to be the limit below which your performance will inevitably suffer. The real-world evidence is against this, however. Researchers in France found that the sub-3hr finishers in the 2009 Mont Saint Michel Marathon averaged 3.1% dehydration, while those who finished in more than 4hrs averaged only 1.8%. A 2013 meta-analysis in the British Journal of Sports Medicine concluded that losses of less than 4% are “very unlikely to impair [endurance performance] under real-world conditions” and recommended that athletes should be encouraged to drink according to thirst.
* Hyponatremia is a dangerous condition in which the sodium concentration in one’s blood has become severely diluted, usually due to excessive sweating combined with drinking large amounts of pure water.
Any cyclist who has experienced a “bonk” will recognise fuel as a limiting factor in endurance performance. There are three basic fuel options for your body: protein, carbohydrate and fat. For fuelling purposes during endurance exercise, carbohydrate and fat dominate. They are used in varying proportions by the body depending on the intensity of the exercise, with carbohydrate becoming increasingly dominant as intensity increases. Hutchinson quotes a study comparing the carb/fat ratio at different paces during a marathon: at 2:45 pace the carbs were at 97%, whereas at 3:45 the carbs had dropped to 68%.
The appropriate mix of protein, carbs and fat in athlete’s diets has been controversial in recent years, with growing enthusiasm for Low Carb, High Fat (LCHF) diets. The theory is that becoming “fat-adapted” can provide an advantage because, even for a skinny trail runner, the fat stored in the body is essentially inexhaustible, whereas the carbohydrate, stored in the form of glycogen, soon runs out.
Hutchinson addresses the LCHF diet controversy in some depth. The science is not yet fully settled but tentative conclusions for all but the most ultra-distance events are that carbs are essential to high performance. LCHF diets do indeed dramatically ramp up fat-burning but they also inhibit carb utilisation and reduce sustained efforts at high intensity. This doesn’t mean there’s no place for LCHF diets in training, as part of a weight-reduction strategy or through personal preference, but most athletes would be well-advised to stick to a well-balanced diet with plenty of carbohydrate.
PART III: LIMIT BREAKERS
In Part I we saw that endurance performance is ultimately limited by the brain. In Part II we looked at the various physical limits to performance and got some glimpses into how the brain moderates physical effort to keep us safe. Finally, in Part III, Hutchinson brings us to consider the key question for all who want to push their limits: how to gain access to at least some of the emergency reserves of energy that your brain protects?
We saw in Part I how, if the effort feels easy, you can go faster; if it feels too hard, you stop. So theoretically anything that moves the “effort dial” in your head up or down should affect how far or how fast you can go, even if it has no effect on your muscles or heart or VO2max.
Increasing perceived effort
Firstly, it is worth noting that stress and mental fatigue move the effort dial UP. This is why a given intensity of effort feels harder after a mentally challenging day at the office, for example, and why it is important to arrive at key events in a relaxed, stress-free state.
Decreasing perceived effort
Without getting into some of the more complex approaches to brain training that Hutchinson writes about, there are numerous accessible ways to self-dial the effort level DOWN.
One of the most simple is to smile. It turns out that smiling releases endorphins which reduce the perceived effort. The effect is present even if the smile is involuntary, caused by holding a pencil in the mouth.
Another fairly simple technique is positive self-talk. Requiring practice and preparation to be effective, the technique has been shown to improve performance in numerous research studies and is very widely used by professional athletes. Use phrases like: “This is what you have been training for”, “Keep pushing, keep pushing”, “You can do it”, “Give it everything”, “Leave nothing behind” or “Almost there, smash it!”
Particularly for cyclists, deliberately relaxing the upper body and shoulders during a climb immediately reduces the perception of effort. Runners are often told to relax their face and jaw.
Taking a caffeine gel just in time for the final push works because it stimulates the release of endorphins, reducing the sense of effort.
Belief can have a significant impact: lucky charms work because their owners believe they do; and telling athletes they look relaxed makes them burn measurably less energy to sustain the same pace.
A boost in self-confidence can result in a break-through performance. Hutchinson relates how Canadian Olympic marathon runner Reid Coolsaet ran the race of his life in qualifying for London 2012. After gaining confidence training in Kenya with some of the world’s best, he took a conscious decision to throw his pacing plan away and just run to stay with the leaders. He finally finished in third place, just outside the Canadian national record (in spite of “atrocious conditions”).
Much more modestly, I had a similar experience on Stage 6 of the 2019 Haute Route Pyrenees. At the end of Stage 5, I was in 3rd place in my age group, 10’24” behind the 2nd place. In a professional race, this would be an unbridgeable gap. In an amateur GranFondo, you never know… Feeling good, and with nothing to lose, I decided to give it my best shot. I started fast and completed the first climb with riders who were normally far ahead of me. Boosted by this, I kept going, and after the ride of my life and in a clear victory for self-confidence I finished the stage 10’47” in front of my rival. (Read the full story here).
Hutchinson’s remarkable book Endure – Mind, Body and the Curiously Elastic Limits of Human Endurance shows that ALL physical training is also brain training, whether targeted as such or not. It has become increasingly clear however that that there are significant benefits to be gained by working very specifically on the psychological factors.
The fact that the mind, which is inherently much less deterministic than the body, has such an important role to play is perhaps what makes sport so endlessly fascinating.
About the reviewer
Marvin Faure is the author of this blog, a British Cycling Level 3 coach and owner of Alpine Cols, a cycling coaching company based in the French Alps. He runs training camps and offers coaching to help amateur athletes perform at their best in mountain sportives and Granfondos.