The Neurobiology of Effort: What Was Your Hardest Race?

Endurance Mindset — Saturday, October 3rd Edition

Eight days until Grant Park. If you're reading this on a Saturday morning without your usual long run weighing on your legs, you've probably already noticed something strange: more free time, and less peace of mind than you expected.

This is the classic taper phenomenon. You cut volume, the body starts to feel fresh — sometimes even odd, with phantom twinges and fatigue that made no sense three weeks ago — and the mind, no longer needing to manage physical tiredness, fills that space with something else: projections. What if I didn't train enough? What if it's hot on race day? What if mile 20 breaks me the way it did two years ago?

That hypervigilant brain isn't malfunctioning. It's doing exactly what it evolved to do: scan the future for threats whenever it detects spare bandwidth. The problem is that, in the absence of real information about what's going to happen on Sunday the 11th, your mind fills the gaps with the worst-case scenario. It's easier to imagine failure than to trust something that hasn't happened yet.

So this week I want to suggest a different exercise: instead of projecting forward, look back.

What the Science Says About the Memory of Effort

There's a principle in cognitive psychology called the peak-end rule, first described by Kahneman and colleagues: we don't remember experiences as a continuous timeline — we remember them by their most intense moment (the peak) and by how they ended (the end). This applies directly to how we store the memory of a brutal physical effort. You don't remember every mile of the marathon that wrecked you two years ago. You remember the hardest moment — and you remember that, somehow, you finished.

That's not a trivial detail. It's operational information. Your nervous system holds a literal, physiological record that you've already crossed the limit and come back. When you consciously retrieve that memory — when you force yourself to reconstruct in detail what it was like, what you thought, what you did with your body and mind at the hardest point — you activate the prefrontal cortex, the region responsible for emotional regulation and deliberate decision-making. That activation, in turn, downregulates the response of the hypothalamic-pituitary-adrenal axis, the system that releases cortisol when the brain detects an anticipated threat (in this case, the marathon that hasn't happened yet).

In plain terms: recalling a past difficulty in detail isn't a nostalgia exercise. It's a concrete neurological intervention against the anticipatory anxiety of the taper.

There's another piece of evidence that supports why this mental work matters as much as the physical kind. Endurance exercise — especially sustained efforts like a long run or a marathon — consistently raises brain-derived neurotrophic factor (BDNF), a protein that strengthens neural plasticity and is linked to better mood regulation and lower stress reactivity [PMID:25455510]. Every long run you completed in this cycle didn't just build your aerobic capacity. It literally reinforced the brain hardware you now need to manage the nerves of the next eight days.

This matters because the physiological stress of the taper is real and measurable. We know, for example, that prolonged exercise produces acute cardiac responses — transient changes in cardiac biomarkers and ventricular function — observed in both young and masters athletes, and that the trained body adapts and recovers these parameters over time [PMID:40667749]. Your heart already knows how to handle the stress of sustained effort; it's done so dozens of times this cycle. And exercise biomarkers — from lactate to inflammatory markers — confirm that physiological adaptation to repeated stress is cumulative and measurable, not an act of faith [PMID:41922043]. You're not blindly gambling on marathon day. You're activating a system that has already proven, with data, that it can handle the load.

The Evidence Is Already in Your Nervous System

Here's the central point of this edition: you don't need to convince yourself you can run 26.2 miles on Sunday the 11th. You need to remind yourself that you already have the proof.

Every athlete who has completed a serious training block has had, at some point, a session or a race that pushed them to the limit. A tempo workout that felt unbearable by mile four. A past race where the final stretch was pure pain and stubbornness. An interval session where the body wanted to stop and the mind didn't.

That moment — however uncomfortable it felt at the time — is now an asset. It's hard data on your own capacity for tolerance, stored not in a spreadsheet but in your own nervous system. Neuroscience tells us that deliberately accessing that memory, reliving it in detail, reduces anxious anticipation because it gives the prefrontal cortex something concrete to work with, instead of letting the amygdala improvise with raw fear.

This Week's Question

Eight days out from Grant Park, I'm asking you directly, coach to athlete:

What was the hardest race or workout you've ever completed?

It doesn't need to be elegant or dramatic. It could be your first 10K, a long run in freezing rain, a race where you walked the last two miles but crossed the finish line anyway. What matters is that you remember it in detail: what went through your mind, what you did with your body, how it ended.

Reply to this email. Seriously — take five minutes this weekend and write it to me. I'll be saving these responses (anonymously, if you prefer) for a special December edition where we'll look together, as a community, at everything we were able to get through this year.

For now, save the mental energy for what actually matters: running strong on Sunday the 11th and sending me your time the moment you cross the line. That's the only forward projection you need to make this week.

Talk soon. Run with what you already know about yourself.

— Coach Henri

References

• Szuhany KL, Bugatti M, Otto MW. A meta-analytic review of the effects of exercise on brain-derived neurotrophic factor. J Psychiatr Res. 2015. [PMID:25455510]
• Frandsen J, Aaroe M, et al. Cardiac Effects of Prolonged Endurance Exercise in Young and Older Athletes. Scand J Med Sci Sports. 2025. [PMID:40667749]
• Siebers M, Bizjak DA. Exercise biomarkers. Adv Clin Chem. 2026. [PMID:41922043]