Exercise Fatigue Is An Emotion

Why your brain quits before your body does, and 6 ways to trick it

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This past weekend’s Two Percent New Year Challenge asked us to log anywhere from one to three total hours of exercise on a cardio machine.

Reader Jonah Losh found himself 20 minutes into a treadmill workout, having forgotten his ear buds, and summed up the experience with this comment: “This is just plain mean.”

Which brings us to today’s letter.

Here’s the big idea: How hard exercise feels is determined less by your muscles than by how your brain interprets time, environment, and meaning.

Raise your hand if you’ve experienced any of the following:

• A 30-minute run on the treadmill feels endless, or, as Jonah put it, “just plain mean” …

• … But that same 30-minute run outside feels manageable, even if you’re running a bit faster.

• Or one day your go-to interval workout feels easy …

• … and three days later, that exact same workout feels brutal.

If any of that sounds familiar, congratulations, your brain is doing exactly what it’s designed to do!

Today, you’ll learn:

• The science of your brain on exercise: How our brain works to limit our performance.

• The central governor theory: Why fatigue is an emotion, not simply a physical state.

• Why some workouts feel harder than others: How clocks and context change your exhaustion.

• 6 ways to go harder yet make it feel easier: Practical tricks to get more gains from each workout.

Quick housekeeping

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• In case you missed it:

  • On Wednesday, we revealed a hierarchy of cardio machines and ranked 9 popular cardio machines into 3 categories: Elite, good, OK in some circumstances. Learn which machines to choose for your goals, and get more from your cardio while also hating it less.

  • Friday’s Expedition post covered 16 new ideas to make you smarter and healthier, including why cancer is becoming a chronic disease, the stark mental health differences between TikTok and Instagram, and new data suggesting fitness outranks sobriety for longevity.

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The central governor theory (or why your brain determines your effort)

For most of modern history, exercise physiologists believed physical exhaustion was simple: muscles ran out of fuel, lactic acid built up, and you slowed down or quit.

But the theory didn’t seem to match reality.

No one had ever proved that muscles were getting too little oxygen or fuel when people hit a wall. What’s more, studies consistently found that even during intense exercise, people recruited only a fraction of their available muscle fibers.

In the mid-1990s, Dr. Timothy Noakes—M.D., Ph.D., director of the Exercise Science and Sports Medicine Research Unit at the University of Cape Town—had an epiphany.

Because we activate muscle through our brain, our brain must also be responsible for determining how long, hard, and fast we push ourselves.

He called the idea the “central governor theory¹,” and began conducting research.

Noakes and others have shown that fatigue during exercise is often a protective emotion. It’s your brain’s way of keeping us from pushing so hard that we hurt ourselves or burn up all our energy.

I spoke to Dr. Noakes, who told me, “Your brain sabotages your performance. When you feel fatigued [during exercise], it’s just a protective emotion. It often has surprisingly little to do with your physical limits².”

The brain uses the “unpleasant (but protective) sensations of fatigue” to pump your body’s brakes well before you come close to real physical exhaustion.

Mind-bending exercise studies

Researchers began testing the central governor theory in clever ways.

In one classic study³, researchers in New Zealand put participants on exercise bikes and told them to pedal until they were totally exhausted. The researchers also casually mentioned, “It would be great if you could last an hour.”

As the participants rode, they could see a clock counting the time they’d been riding.

But here’s where it gets devious: the clock was secretly manipulated.

• With some participants, they secretly slowed down the clock.

• With others, they secretly sped it up.

• With others, the clock was accurate.

Nearly everyone said they were exhausted and quit when the clock read about one hour—even though some had actually ridden 10 to 30% longer or shorter than an hour.

Importantly, the participants really did feel exhausted—their brains just decided when exhaustion should arrive.

Their limit wasn’t physical. It was between their ears: That early cue from the researchers—“it would be great if you could last an hour”—had given them a psychological goalpost of when to feel exhausted.

Maybe you’ve noticed something like this yourself: If you go out for a 5-mile run, you might start to feel tired at mile 4. But if you go out for a 10-mile run, you’ll feel fine at mile 4 and tired at mile 9. Your expectation sets how you feel.

The brain appears to use time, distance, and environmental cues as part of its internal cost-benefit calculation (“how long have I been at this?”).

Emotions matter

The Brazilian researcher Eduardo Fontes, Ph.D., studied cyclists’ brain activity using fMRI while they pedaled to exhaustion.

As their intensity increased, the activity in their limbic system—the brain’s emotional center—increased too. The more emotion cyclists attached to exertion, the more they slowed down.

Fontes told me that our mental state is behind much of the variation in our day-to-day performance. “Anyone who works out knows that training performance can differ drastically from one session to the next,” he says. “Physiologically, you might not have changed; what may have changed substantially is your mental state.”

This explains why the same workout can feel wildly different from one day to the next. Time cues, your environment, the meaning you get from a specific exercise, and your mood all feed into how hard exercise feels—even when your physical fitness stays the same.

“Your biology sets your true limit, of course, but how close you get to it is determined by what you believe,” Dr. Noakes told me.

Now that we know our brain can hold us back or push us closer to our true limit, here’s how you can use that information.

The point isn’t to override your brain—you can’t do that. But you can work with it. Here are 6 tips and tricks to make doing more exercise easier so you can get closer to your real limits.

1. Get Zen

Fontes found that people who can detach from their emotions during exercise—for example, not thinking about their panting breaths or burning legs—almost always perform better.

“When you exercise or compete, you have to mentally process what’s happening to your body,” he told me. “But the key is to not judge it as positive or negative; that’s when your brain sets limits.”

Dr. Larry Shapiro, who wrote Zen and the Art of Running, gave me this advice: “Let’s say you’re heading up a big hill,” said Shapiro. “Instead of giving some negative valence to the experience, think about what’s happening to you internally without judgment, how the elevation is affecting your breathing, how your legs feel.”

I.e., Notice the sensations without labeling them as bad. And if you do want to slap on a label, make it a good one. Like, “my legs feel this way because they’re getting fitter.”

2. Use distance rather than time

Running a distance often feels easier than running for a certain amount of time.

There are a variety of reasons for this, but they generally come down to the fact that distance gives you progress while time sits there watching you.

• Our perception of time slows when we exercise⁴. A clock only reinforces that dragging feeling, making exercise feel like it “goes on forever.”

• People will often slow down to “get through” a duration—but that limits the amount of work they do. For example, if you decide to run for 45 minutes, you can slow down to get through it more easily. Distance guarantees the same amount of total work.

If you’re on a cardio machine, put a towel over the clock and just go. That’ll prevent you from feeling like time is dragging.

3. Go outside

There’s this thing called the “green exercise” effect⁵. It states that outdoor exercise often feels easier and passes by quicker—even when we’re exerting the same effort or more.

This is likely because nature offers three ingredients that humans love: freedom, variability, and novelty.

• Freedom is the number of things you can do in a given environment.

• Variability means that things change often.

• Novelty refers to things that are new and original.

No matter the circumstances, the more freedom, variability, and novelty we have, the better we’ll generally feel.

In the context of exercise, those three things pull our attention outward—and when attention moves outward, effort feels lighter.

The view and terrain change with every step, new challenges arise, we can turn left or right, and we see new things along the way. This gets you out of thinking about your discomfort and into paying attention to the outside world.

Cardio machines offer basically no freedom, variety, and novelty: You move in one direction and nothing much changes.

Researchers in the UK looked at the research and wrote:

Outdoor natural environments may provide some of the best all-round health benefits by increasing physical activity levels with lower levels of perceived exertion, altering physiological functioning including stress reduction, restoring mental fatigue, and improving mood and self-esteem and perceived health.

4. Make it less boring

I’ve written at length about the benefits of boredom in our screen-driven world, where the average person spends more than 12 hours a day engaging with digital media.

In daily life, resisting the easy fix for boredom (more screens) and sitting with it for a moment can lead to creative ideas and productive tasks.

But when you’re exercising, boredom often just magnifies discomfort and makes you slow down, quit, or suffer more—so please feel free to ignore my typical advice.

When nothing engages our attention as we exercise, we tend to fill the space by monitoring our burning legs and lungs and general discomfort. The more we monitor it—as Fontes taught us in point 1—the worse we perform and the more arduous the exercise feels.

There are many ways to make exercise less boring:

• Take it outside, as noted above.

• Use a cardio machine like Zwift or Peloton that has a social competition element that gives you microgoals to complete during a workout.

• Create your own microgoals. E.g., Instead of 30 straight minutes, do 5 minutes hard, 5 minutes easy for a total of 30 minutes.

• Do interval-style workouts where you switch from one exercise to another or between machines, which breaks up the monotony.

• Watch a show as you exercise. I recently put a TV in my garage gym—and it incentivized me to exercise more. Now, I’ll time my workouts to Golden Knights games. My thinking: “If I’m going to watch sports, I might as well watch them while exercising.”

5. Use music

There’s a good reason military units used to march long distances into battle with musicians in tow: Exercise ramps us up and helps lower our perception of effort.

A big chunk of research shows that music makes exercise feel easier. Good music lowers perceived effort, improves mood, and helps people keep going longer—even when the workout and real effort stay exactly the same.

What’s happening is pretty simple: rhythmic, motivating music pulls your attention away from your breathing, burning legs, and internal whining, and gives your brain something motivating. Time passes faster, and effort feels more manageable.

One thing that’s helped me is having certain songs or playlists for specific workouts: For example, I have playlist for longer runs and another for all-out intervals. Think: Grateful Dead live show for runs, punk playlist for intervals.

You can also use playlists instead of timers. E.g., run slower for one song, faster for the next, etc. It’s the same basic structure without a timer.

• Caveat: I do think people can become too reliant on music or podcasts when exercising. E.g. “I didn’t exercise because I couldn’t find my AirPods.” We don’t want that to happen, and it does make sense to train a tolerance to silence during workouts.

  • My fix: When I do trail runs, I run most of it in silence. Then, in the final quarter of the run when I’m tired, I blast music, which gives me a lift when the run is hardest.

6. Reset your goalpost (I.e., go really f*cking long)

Something strange has happened to me since I hiked the 850-mile Hayduke trail: I’m terrible at estimating how far I’ve hiked. I now underestimate by about 50 percent.

This happened during a recent trip to Joshua Tree with my friend Matt Sherman. I thought we’d hiked about 10 miles. We’d done 22.

I think this phenomenon is rather simple: Hiking the Hayduke trail—which required about 25 miles a day—trained me to be “used to” walking all day. I pushed my internal goalpost for what constitutes a long hike.

Long efforts sort of “reset” your brain’s sense of what’s reasonable. E.g., Once you’ve run or hiked 20 miles, 6 is no big deal.

The takeaway: go through periods where you work up to long durations of exercise. They’ll be hard in the moment, but they can give you a new goalpost that makes your future (regular) workouts easier.

Have fun, don’t die, don’t think,

-Michael

Audio Version

1. Noakes, T. D. (2011). The central governor model and fatigue during exercise. In F. E. Marino (Ed.), Regulation of fatigue in exercise (pp. 1–26). Nova Science Publishers, Inc.

2. Note: Not everyone agrees with every detail of the central governor model. But nearly everyone agrees on the core finding: perception, expectation, and emotion shape performance in powerful ways.

3. Morton, R. H. (2009). Deception by manipulating the clock calibration influences cycle ergometer endurance time in males. Journal of Science and Medicine in Sport, 12(2), 332–337

4. Edwards AM, Menting SGP, Elferink-Gemser MT, Hettinga FJ. The perception of time is slowed in response to exercise, an effect not further compounded by competitors: behavioral implications for exercise and health. Brain Behav. 2024 Apr;14(4):e3471. doi: 10.1002/brb3.3471. PMID: 38558543; PMCID: PMC10983804.

5. Gladwell VF, Brown DK, Wood C, Sandercock GR, Barton JL. The great outdoors: how a green exercise environment can benefit all. Extrem Physiol Med. 2013 Jan 3;2(1):3. doi: 10.1186/2046-7648-2-3. PMID: 23849478; PMCID: PMC3710158.