What if the biggest limiter on your next run isn’t your legs, your lungs, or your lactate-but your mind?
Two dominant models attempt to explain what makes endurance athletes stop:
- The Central Governor Theory, popularized by Dr. Tim Noakes, argues that your brain acts as a protective mechanism-shutting you down before your body incurs damage.
- The Motivational Intensity Theory, championed by Dr. Samuel Marcora, says you stop when the effort simply no longer feels worth it. Not because you’re unable, but because you’re unwilling.
These ideas aren’t just academic-they show up on every long run, every race, and even in training.
The Central Governor Theory (CGT):
Developed in the 1990s, CGT proposes that the brain limits physical exertion by reducing muscle activation once danger signals arise (like overheating, glycogen depletion, or acidosis). It does this subconsciously, to keep you alive and injury-free.
You might feel like you’re slowing down due to fatigue, but CGT argues it’s your brain’s calculated decision based on perceived threats to homeostasis.
👨⚕️ Further Reading:
The Lore of Running – Tim Noakes
An Interview with Dr. Noakes – Marathon Training Academy
The Motivational Intensity Theory (MIT):
Dr. Marcora’s model, in contrast, centers on conscious motivation. His research showed that cyclists could perform maximal sprints immediately after claiming to be “exhausted” from a submaximal time trial.
The implication? Physical reserves still existed-they just chose to stop because the effort no longer seemed worthwhile.
🔬 Key Study:
Marcora et al. (2009) – “Mental fatigue impairs physical performance in humans.”
Journal of Applied Physiology
How This Played Out in My Training
During my August 3 long run, I felt a wave of fatigue roll in at the 80-minute mark. Heat, elevation, and cumulative effort were adding up.
But something shifted:
I told myself, “Only 30 minutes left. That’s three 10-minute chunks.”
Then I started calculating my pace per segment…
And wouldn’t you know it-I surged.
My HR didn’t spike disproportionately. My legs didn’t collapse. In fact, I got smoother. Maybe it was the final gel kicking in. But maybe-just maybe-it was the Marcora effect: I re-engaged.
Real-World Takeaways for Runners Over 50:
✅ Train the Mind, Not Just the Body: Discomfort tolerance is a skill. Mantras, visualization, and reframing can keep you in the game longer.
✅ Monitor RPE Alongside Metrics: If your watch says you’re fading but you feel okay, maybe you’re not truly out of gas-just unmotivated.
✅ Beware of the False Stop: Ending a session doesn’t always mean you’re “done.” It might just mean your reason to continue lost the internal debate.
Conclusion:
Both theories offer insight. Your body has real physiological limits. But you also carry an untapped reserve, waiting to be called upon when the moment (and motivation) is right.
Next time you feel yourself backing off, ask:
Is this really fatigue-or am I just done trying?