The Science of Suffering (Part 2)

In Part 1 of this episode, we explored how discomfort shapes endurance, why the brain – not the body – decides when to stop, and how perceived effort plays a crucial role in pushing limits. We uncovered that discomfort is not an absolute barrier but a mental construct that can be trained and regulated.

Now, in Part 2, we go deeper into the science behind perceived effort and mental fatigue. Why does effort feel harder under certain conditions? How do elite athletes develop a higher tolerance for discomfort? And most importantly, how can you train your brain to push further when it matters most? Understanding these mechanisms will help you master endurance – not just physically, but mentally.

At the heart of the psychobiological model of endurance lies one key concept: the perception of effort. This is not a direct measure of how hard your muscles are working – it’s your brain’s subjective interpretation of how hard the effort feels. The psychophysical scales commonly used to monitor perception of effort are: (i) the rate of perceived effort (RPE) scale, (ii) the category ratio scale (CR) 10 (often integrated in fitness tracker) and (iii) the CR100 scale. These range from no effort at all to maximum exertion, but differ in the granularity if one subject moves from one level to another.

The neurophysiology behind this process is complex and not yet fully understood. However, research suggests that the perception of effort is closely tied to activity in brain regions responsible for driving muscle contraction. The harder and longer you push, the more these areas of the brain fire up. What you feel as effort is not the direct strain in your muscles, but rather the conscious awareness of the motor commands your brain is sending to sustain movement. In simple terms: effort is a sensation generated in the brain, not in the muscles.

This concept is critical when considering endurance limits. In constant-load exercise, the psychobiological model suggests that athletes will continue until they reach the highest level of effort they are willing to tolerate. In other words, exhaustion isn’t purely about what the body can do, but about what the mind is willing to endure. This idea is supported by studies examining athletes’ ability to tolerate high levels of discomfort. Time and time again, findings reinforce a hard truth: when all else is equal, the gold medal goes to the athlete who is willing to suffer just a little more than everyone else.

Elite endurance athletes are able to tolerate significantly higher levels of effort compared to less trained individuals. Whether this is a natural predisposition – some people simply feel less effort for the same workload – or a consequence of years of training remains an open question. However, there is increasing evidence that structured endurance training, particularly high-intensity workouts that force athletes to confront discomfort, actively increases one’s tolerance for suffering.

This means that mental resilience isn’t just a talent – it’s a skill. A trainable, adaptable quality that allows athletes to push their limits further than they once thought possible. And that’s the essence of elite endurance performance: it’s not just about physical capacity, but about the mind’s ability to endure discomfort, interpret effort, and keep going when everything is telling you to stop.

There’s a twist in the endurance puzzle – your brain itself can become fatigued. And when it does, everything feels harder. Research shows that performing a mentally demanding task before exercise can significantly impact endurance performance. Athletes in these studies quit sooner or rated the same physical intensity as more demanding when mentally fatigued. What’s particularly fascinating is that traditional physiological markers of endurance – heart rate, blood lactate, oxygen uptake, cardiac output, even VO₂ max – remained unchanged. In contrast, maximal strength, power, and anaerobic performance were largely unaffected by mental fatigue.

This led researchers to an important conclusion: the longer and more intense the physical effort, the more mental fatigue matters. And the key reason? A heightened perception of effort.

Mental fatigue and perceived exertion go hand in hand. In fact, the impact is so strong that some scientists speculate mental fatigue might be a primary cause of increased effort perception – a direct limiter of endurance performance. But unlike physical fatigue, where we can measure lactate buildup or muscle glycogen depletion, or unlike sleep pressure, where adenosine accumulates in the brain, the exact substance responsible for this effect remains unknown.

Interestingly, professional athletes seem to have a higher resistance to mental fatigue compared to non-professionals. While non-professionals show a significant decline in endurance performance after a mentally draining task, elite athletes can maintain their performance level for much longer. This suggests that years of training not only improve physical endurance but also build a kind of cognitive endurance – the ability to resist the negative effects of mental fatigue.

When we think of endurance, we often picture marathons, triathlons, or ultra-distance races. But from your brain’s perspective, endurance starts much sooner – after just 30 seconds of sustained effort. Whether it’s a 400-meter sprint, a high-intensity rowing piece, or a long climb on the bike, the principles we’ve discussed apply to any activity where effort must be voluntarily sustained over time. As six-time Ironman champion Mark Allen put it: Endurance racing is a test of you as a person on top of a test of you as an athlete. So, how do we put the pieces together? What practical lessons can we take from this knowledge?

1. Training Changes Perception – And Increases Tolerance: Training doesn’t just build physical strength; it reshapes how your brain perceives effort. The more familiar your brain is with discomfort, the less threatening it becomes. With training the same intensity is rated less effortful. In addition, elite endurance athletes can push closer to their true physical limits before they reach their psychological tolerance for suffering. From a psychobiological perspective, endurance performance is a form of self-regulation – the ability to control internal states and behavior in pursuit of a goal. This means your training should include tolerance training for high levels of discomfort. Gradually increasing exposure to discomfort builds resilience. The key? Train in conditions as close as possible to real race situations. Make your brain know the effort, so it no longer triggers an exaggerated warning response.
2. Discomfort Is Subjective – You Still Have More Left: Even when you feel like hell, your body still has more in the tank. This doesn’t make the suffering feel any less real – but recognizing this truth is a powerful mindset shift. The perception of effort is what convinces you to slow down, not actual physical depletion. Keep this in mind when discomfort peaks: your body can still go on.
3. Discomfort Is an Emotion – And Can Be Regulated: At its core, discomfort is an emotion, just like fear or anxiety. And emotions can be trained and regulated. This is where mental training becomes crucial. Athletes who develop emotional regulation strategies – through mindfulness, or cognitive training – can manage discomfort more effectively. Mindfulness, for example, helps athletes regulate their responses to other emotions, and research shows it work similarly with discomfort. The best athletes aren’t those who feel less discomfort – they are the ones whose illusionary symptoms interfere the least with their actual performance.
4. The Battle Against Discomfort Happens on Two Levels: Your fight with discomfort happens on both a conscious and subconscious level. Even if you’re not actively thinking about it, your brain is constantly managing the effort – adjusting, regulating, and resisting the urge to slow down. This mental processing is energy-intensive, and when mental energy runs low, mental fatigue sets in – making the effort feel even harder. Studies show that elite athletes are better at resisting the negative effects of mental fatigue. Their brains run more efficiently, and even when mentally drained, they can still tolerate high levels of effort. This suggests that over time, endurance training strengthens metacognitive processes – allowing athletes to manage discomfort with greater control, even when depleted.

This also highlights the importance of starting a race or key training session mentally fresh, well-rested, and properly fueled – since, unlike muscles, the brain cannot store energy and depends entirely on blood sugar to function optimally.

Discomfort isn’t a barrier – it’s a test. A test of how well you regulate your perception of effort, how effectively you train your tolerance, and how much mental resilience you’ve built. The athletes who rise to the top aren’t necessarily the strongest or the fastest. They are the ones who suffer “smarter”.