Brain Activity During Running: The Theory of Central Fatigue and the Runner's High

Introduction

Every marathon runner has experienced this moment: the body screams “stop,” but the brain (or some deeper will) keeps you moving forward. There’s also that other moment: when everything feels just right—light footsteps, a joyful mood, almost forgetting you’re running—this is the coveted “Runner’s High” that runners dream of.

These two extreme experiences point to one fact: the brain is the most important organ in running. Sports physiology research is revealing that both fatigue and the runner’s high are products of complex neural activity in the brain, not merely muscular issues.

Central Fatigue Theory

Limitations of the Traditional “Peripheral Fatigue” Model

Traditional sports physiology attributes fatigue to peripheral factors: muscle glycogen depletion, lactic acid accumulation, ATP depletion… However, this model cannot explain one phenomenon: a runner who is “exhausted” and unable to continue can often instantly sprint upon seeing the finish line. If the muscles were truly depleted, this would be impossible.

The Central Governor Model

South African sports scientist Tim Noakes’ “Central Governor” theory proposes that:

• The brain (especially the premotor cortex) continuously monitors bodily states (temperature, blood glucose, muscle damage, cardiac load, etc.)
• Based on this information, the brain actively reduces neural drive intensity to protect the body from exceeding dangerous limits
• The “fatigue” a runner feels is partly a “protective warning signal” generated by the brain, rather than a true depletion of bodily resources

This explains why marathon runners can accelerate upon seeing the finish line—the brain “calculates” that a safe distance has been reached and releases more of its reserved neural drive.

Brain Neurochemistry During Running

During running, multiple neurotransmitters in the brain undergo dynamic changes:

The Serotonin–Fatigue Connection

After prolonged running, serotonin (5-HT) levels rise, which is directly linked to increased fatigue:

• Serotonin reduces exercise motivation by inhibiting dopaminergic neurons
• Branched-chain amino acids (BCAA) compete with tryptophan (a serotonin precursor) for entry into the brain; BCAA supplementation may slightly delay central fatigue (theoretically effective, though experimental results remain debated)

The Neuroscience of the “Runner’s High”

The Endocannabinoid System: The Star of the Runner’s High

A 2021 study published in the journal Neuroscience provided strong evidence that the runner’s high is primarily mediated by endocannabinoids, rather than the traditionally assumed endorphins:

• Blood levels of anandamide (AEA, a cannabinoid receptor ligand) rise significantly after long runs
• Cannabinoid receptors are widely distributed in the brain’s limbic system (involved in emotion) and the prefrontal cortex
• Endorphin molecules are relatively large and struggle to cross the blood-brain barrier, making it difficult for them to act directly on the brain

When Does the Runner’s High Occur?

Not every run produces a high. Research indicates the triggering conditions include:

• Intensity: Approximately 60–75% VO2max (moderate intensity, not “all-out effort”)
• Duration: Typically appears after 60–90 minutes of continuous running
• State: Running after adequate rest; harder to trigger when fatigued
• Environment: More likely outdoors in natural settings than on a treadmill

Taiwanese runners jogging along the Tamsui River or in the Guandu Plain at sunrise can sometimes capture this high, enhanced by the natural environment.

Mental Toughness and Running Performance

Dissociation and Association Strategies

Research shows that runners use different attentional strategies in different situations:

• Dissociation: Shifting attention away from bodily sensations to external stimuli (music, scenery, plans)—suitable for easy runs, can reduce perceived fatigue
• Association: Focusing on bodily signals (cadence, breathing, muscle sensations)—suitable for racing, helps precisely control pace

Studies show that elite marathon runners tend to use association strategies during races, while recreational runners lean toward dissociation.

The Neural Mechanism of “Hurting but Continuing”

In the latter stages of a marathon, activity in the anterior cingulate cortex (ACC)—the brain region that processes pain and executive decision-making—increases significantly. A runner’s ability to continue through fatigue results from the coordinated action of the ACC and the dorsolateral prefrontal cortex (dlPFC): the cognitive control system continuously overrides the “stop” signals coming from the sensory system.

Meditation and Running: Integrating Brain Training

Recent research shows that mindfulness meditation can strengthen a runner’s central fatigue resistance:

• Regular meditation practice can increase gray matter density in the dlPFC, enhancing executive control
• “Mindful Running”—consciously observing bodily sensations without judgment—has been reported by some runners to delay perceived fatigue
• Taiwanese runners can try 15–20 minutes of mindfulness meditation 2–3 times per week as a training supplement

Practical Recommendations

• Positive self-talk and setting clear goals before a run can delay the subjective feeling of central fatigue
• Using music (especially tracks with a BPM close to your target cadence) can effectively employ dissociation strategies, reducing perceived fatigue during easy runs
• Deliberately incorporate practice of “continuing to run under mildly uncomfortable fatigue” into training to build the brain’s tolerance for discomfort
• Running in Taiwan’s natural environments (such as Guandu or Dajia Riverside Park at dusk) combines natural stimuli, making the runner’s high easier to trigger
• Adequate sleep is the foundation for optimal brain function during running; a sleep-deprived brain generates “stop” signals earlier

Conclusion

The brain is the true battleground of every marathon. Central fatigue theory tells us that running limits are determined not only by muscles, but also by how the brain interprets and responds to bodily signals. The runner’s high reminds us that the brain is equally the source of running’s deepest joy. While training your body, also train your brain—this is truly comprehensive road-running preparation.

Related Reading

• The Science of Fatigue in Running: How Central and Peripheral Fatigue Jointly Determine Your Limits
• Where Does the “I Want to Quit” Thought Come From? A Complete Analysis of the Central Governor Theory
• Neural Fatigue Monitoring in Running: Research on Measuring Preexercise Neural Transmission and Central Drive
• Neuromuscular Fatigue in Running: The Science of Recovery After Long-Distance Runs