WHY LONG-DISTANCE RUNNERS DON'T BUILD BIG MUSCLES
- Koray Y.
- Oct 20
- 3 min read
When we see long-distance runners gliding lightly over miles of road, one thing stands out: their bodies are lean, efficient, and built for endurance — not size. But why don’t their muscles grow larger, even though they train intensely for hours every week?
The answer lies in how the body adapts to different types of stress. Let’s explore what really happens inside the muscles of endurance athletes — and why their strength looks different from that of a bodybuilder or sprinter.
Different Goals, Different Adaptations
Our muscles respond precisely to the kind of challenge we give them.
Endurance training teaches the body to use oxygen efficiently and keep working for long periods.
Strength training tells the body to produce more force and grow larger muscles to handle heavy loads.
A runner’s body learns one simple lesson from years of distance training:
“Be efficient, not big.”
The Science Behind It
Endurance exercise activates a cellular signal called AMPK, which helps the body build more mitochondria — the tiny power plants inside our cells. More mitochondria mean better energy production and greater stamina.
Strength training, on the other hand, activates mTOR, a pathway that promotes muscle growth. Interestingly, AMPK and mTOR work in opposite directions. When the body focuses on endurance, it naturally suppresses muscle-building signals — because larger muscles would require more oxygen and energy to maintain.
Muscle Fibers Matter
We have two main types of muscle fibers:
Slow-twitch fibers (Type I) – great for endurance, fatigue slowly, smaller in size.
Fast-twitch fibers (Type II) – powerful, grow quickly, fatigue faster.
Long-distance runners mainly use slow-twitch fibers, which adapt by becoming more efficient rather than larger. Over time, this results in a lean, toned, and highly capable body — but not a bulky one.
Recovery and Energy Balance
Endurance athletes often train for many hours each week, sometimes twice a day. This creates a large energy demand. To maintain performance, their bodies use calories primarily for recovery and repair, not for building new muscle tissue.
Moreover, carrying extra muscle mass would increase the energy cost of every step — exactly the opposite of what an endurance athlete needs.
Strength Without Size
Even though their muscles don’t grow much in volume, endurance athletes still become stronger — just in a different way. Their improvements come from:
Better coordination between nerves and muscles
More oxygen-rich capillaries surround each muscle fiber
Greater resistance to fatigue
It’s not about appearance. It’s about efficiency and performance.
What We Can Learn
This principle applies beyond running. Whether you’re cycling, swimming, or practicing yoga, your body will always adapt to the kind of stress you give it.
If you want endurance and stability, train consistently and stay aerobic.
If you want more power or tone, include some resistance work. Balance is the key.
At Waha
At Waha, I see many endurance athletes — cyclists, runners, and active professionals — who rely on their bodies every day. Understanding how your muscles adapt helps you take better care of them. Massage therapy supports these adaptations by improving circulation, reducing recovery time, and helping your muscles maintain their natural elasticity and efficiency.
Your body is always listening to what you ask of it.
Train it wisely, care for it deeply, and it will serve you beautifully.
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