# Mitochondrial density

Mitochondrial density is how many mitochondria you have per unit of muscle. It also covers how much space they take up. Higher density means more capacity to burn fuel with oxygen. So you can burn more fat and pyruvate aerobically. That improves endurance and metabolic flexibility. Aerobic and Zone 2 training build new mitochondria. They do it via a master regulator called PGC-1α. Age and inactivity reduce density. Keeping yours up is considered central to healthy aging. It also matters for heart-and-lung fitness.

## Sources

- Holloszy JO. (1967). Biochemical adaptations in muscle: effects of exercise on mitochondrial oxygen uptake and respiratory enzyme activity in skeletal muscle. Journal of Biological Chemistry. https://doi.org/10.1016/S0021-9258(18)96046-1

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_Canonical: https://longevity-switzerland.com/en/glossary/mitochondrial-density · Part of Longevity Cities · Updated 2026-06-22_