What are mitochondria?
Mitochondria are tiny structures inside your cells that turn the food you eat and the oxygen you breathe into energy your body can actually use.
Think of each cell as a small town and mitochondria as its power plants. When the power plants run well, the lights stay on, the factories hum and the trash gets collected. When they fail, the whole town slows down, even if nothing else is wrong.
Why it matters for aging
A typical cell holds hundreds to thousands of mitochondria. Energy-hungry tissues like your heart, brain and muscles hold the most. They make a molecule called ATP, the "energy currency" that powers almost everything your cells do, from moving a muscle to firing a thought.
With age, mitochondria tend to become fewer, less efficient and harder to clear out when damaged. Scientists count this as one of the twelve hallmarks of aging. It's a big part of why energy, stamina and recovery often fade over the years.
The good news: mitochondria respond to how you live. Training, especially endurance and interval work, is a powerful signal for your body to build new mitochondria and recycle worn-out ones.
A common myth
Mitochondria are just batteries. Take enough "energy" supplements and you'll fill them up.
Mitochondria are living, changing parts of your cells. They also send signals, help decide when a damaged cell should die, and multiply or shrink depending on how you live. The strongest known way to build more and better ones is regular exercise, not a pill.
Go deeper
Deep dives
- Why am I always tired after 40? The upstream answer
- The first part of you to break isn't in your nucleus
Related terms
Updated Nov 7, 2026 · All terms