What a Marathoner Sees
In What I Talk About When I Talk About Running (2007), Haruki Murakami repeats a simple line: 'I don't run to become someone else. I run to remain who I am.' From a novelist who has logged 10 km a day for thirty years, this sentence captures the runner's high better than most exercise physiology textbooks — it is less euphoria than return to self.
Neuroscience, however, takes nothing on faith. What molecules pour out of the brain during a long run? Which circuits go quiet? What lifts depression and anxiety? Over the past two decades, PET scanners, knockout mice, and randomized trials in thousands of depressed patients have hunted these answers.
What PET Saw — Boecker 2008
Henning Boecker's 2008 paper in Cerebral Cortex gave us the first direct human evidence for the runner's high. Ten trained endurance runners ran for two hours, then lay in a PET scanner injected with [18F]diprenorphine — a tracer that competes with endogenous opioids for receptor binding. Where the tracer's signal weakens, your own opioids have been at work.
The result was clean: opioid binding dropped significantly in the prefrontal and anterior cingulate cortices — exactly where your endogenous opioids had flooded the receptors. More importantly, the magnitude of that drop correlated with runners' self-reported euphoria. Thirty years of folklore about 'endorphins' finally had human imaging behind it.
But the Real Star May Be a Different Molecule — Fuss 2015
The story did not end there. In 2015, Johannes Fuss and colleagues published a mouse study in PNAS that shook the endorphin hypothesis. They let mice run voluntarily on wheels, then administered two antagonists separately.
- Opioid blocker (naloxone): the running-induced anxiolysis remained.
- Cannabinoid blocker (rimonabant): the running-induced anxiolysis vanished.
The conclusion was provocative. At least in mice, post-exercise calm is not driven by opioids but by endogenous cannabinoids — the body's own cannabis-like molecule, anandamide. Opioids may add to the flavor of euphoria, but they are not the switch that turns anxiety off. Raichlen's 2013 J Exp Biol work added a wrinkle: humans and dogs show post-exercise endocannabinoid spikes, but ferrets — sedentary by nature — do not. The reward circuit fires only in species evolved to run.
A third hypothesis exists. Dietrich and McDaniel's (2004) transient hypofrontality model proposes that prolonged exercise actually reduces prefrontal activity. The circuits that handle self-criticism, planning, and rumination go quiet for a while, blurring time and producing the meditative 'here-now' state runners describe.
Three Hypotheses for the Runner's High
| Hypothesis | Mechanism | Key evidence | Limits |
|---|---|---|---|
| Endogenous opioids | Prolonged running releases β-endorphin etc. in prefrontal/anterior cingulate, activating μ-receptors | Boecker 2008 PET: receptor occupancy correlates with euphoria | Opioid blockers don't kill the anxiolysis (Fuss 2015). Contributes to euphoria/analgesia but not full explanation |
| Endocannabinoids | Anandamide (eCB) crosses BBB, activates CB1 receptors → anxiolysis, analgesia, relaxation | Fuss 2015 PNAS: rimonabant abolishes anxiolysis. Raichlen 2013: eCB rises in humans and dogs post-exercise | Human causal proof still limited. Not uniform across intensities/durations |
| Transient hypofrontality | Metabolic load of sustained exercise lowers prefrontal activity, quieting self-referential and ruminative circuits | Partial fMRI evidence (Dietrich 2006); fits time-distortion and flow reports | Hard to measure directly. May be redistribution rather than 'shut-off' |
Which is right? Not settled. But these hypotheses are not mutually exclusive. Anandamide turns off anxiety while opioids add the glow, and the prefrontal cortex steps back so the loop of me falls silent. The runner's high is almost certainly an ensemble, not a solo.
Can It Match a Pill? — SMILE and After
Clinically, the more urgent question is whether running can match medication for major depression. In 1999, James Blumenthal's Duke team published the SMILE trial (Standard Medical Intervention and Long-term Exercise) in Archives of Internal Medicine. They randomized 156 depressed adults aged 50+ to (1) sertraline alone, (2) aerobic exercise alone (three 45-min sessions per week, mostly running/brisk walking), or (3) both combined.
At 16 weeks, remission rates were statistically indistinguishable. Drugs and running performed similarly; combining them did not produce dramatic synergy. The more striking finding came in the 2007 Psychosomatic Medicine follow-up: at 10 months, the exercise arm had lower depression relapse than the medication arm. The more patients continued exercising, the lower their relapse risk.
Felipe Schuch's 2016 meta-analysis in J Psychiatr Res pooled 25 RCTs. Adjusted for publication bias, the standardized mean difference for exercise on depression was −1.11 — clinically a 'large effect.' Stubbs's 2017 meta-analysis showed similar benefits for anxiety disorders.
Two caveats. First, the strongest data are for mild to moderate depression and anxiety. In severe depression or active suicidality, exercise is not a substitute for medication and psychotherapy but an adjunct. Second, although many trials used running, cycling, swimming, and HIIT show similar effects. There is no strong evidence that running is superior to other aerobic forms. Running's edge is access — a pair of shoes and the front door.
The Brain Itself Grows — BDNF and Hippocampus
The long-term effects are even more interesting. Aerobic exercise increases BDNF (brain-derived neurotrophic factor), a protein that supports synaptic growth and neuronal survival — fertilizer for the brain.
Kirk Erickson's 2011 PNAS trial went further. Among 120 adults averaging 67 years, those assigned to a year of moderate walking/running three times per week showed hippocampal volume increase of about 2%, while a stretching/balance control group shrank by ~1%. The hippocampus is the seat of memory and emotion regulation. They had effectively rewound a year of aging.
Korea's Running Landscape
Since 2022, running in Korea has become a culture, not just exercise. More than a hundred running crews now line the Han River; company-based running clubs have proliferated; trail running fused with traditional mountain hiking has its own following. Lee Byung-hak's Running and Meditation (2020) offers a Korean-flavored counterpart to Murakami — running as a training of attention: deliberately following breath, foot, and landscape.
With marathon fatalities reported every year, the Korean Society of Cardiology emphasizes: ① cardiovascular screening for first-time full-marathoners over 40; ② no surge pacing; ③ a minimum 16-week build-up; ④ avoid extreme heat and high particulate days. Pedisic's 2020 meta-analysis is encouraging: any amount of running lowers all-cause mortality, with benefits appearing from as little as ~10 minutes per day. A marathon does not have to be the goal.
The Dark Side: Overtraining and Exercise Addiction
The same molecule can be medicine or trap. Pushed to the edge daily, cortisol stays chronically high, sleep deteriorates, mood paradoxically sinks — overtraining syndrome. Berczik's 2012 framework for exercise addiction includes ① withdrawal (anxiety, irritability) without running; ② running through injury; ③ workouts that wreck work and relationships; ④ escalation to feel the same satisfaction — closely paralleling DSM behavioral-addiction criteria.
The fact that the runner's high is a real neurological reward also means it can become an object of dependence. The self-check question is simple: Do I choose running, or does running drag me?
Five Rules for Beginners
- Start with 3×/week × 30 min. For the first four weeks, walk-run intervals (run 1 min, walk 2 min, repeat 8×) are enough.
- Pace = conversational. You can talk in full sentences without breaking. Heart rate around 60–70% of max.
- Increase weekly mileage by ≤10%. The biggest cause of injury is ramping too fast.
- One pair of shoes: ~6 months / ~600 km. When cushioning dies, your knees pay.
- Five minutes of nothing right after. The strongest neurological after-effects of running peak in the 30 minutes post-exercise. Treat that window like a meditation.
Conclusion: Not Shoes Instead of Pills, but Shoes Alongside Them
Running is not the only answer to depression or anxiety. But it does something no drug can mimic — it lifts cardiovascular health, musculoskeletal strength, cognition, and mood at once; it provides social connection (a crew); it restores self-efficacy; instead of side effects it leaves byproducts (fitness).
The light Boecker saw on PET, the anandamide in Fuss's mice, the patients in Blumenthal's trial who recovered without a pill — all of it converges on one sentence. Calm of mind is evolutionarily rewarded in animals that move. Our brains were built to run. Using that design is the oldest form of self-care.
