Mitochondria are the organelles inside almost every human cell that convert food and oxygen into ATP, the chemical energy the rest of the cell runs on. The shorthand “power plants” is accurate but incomplete: they also buffer calcium, produce heat, help launch programmed cell death, and act as signaling hubs under stress. Unusually for an organelle, each one carries its own small circular genome, inherited from your mother and separate from the DNA in the nucleus. The reference entry on Mitochondria works through the same material in more depth.
What it measures
A mitochondrion is a structure, not a number on a lab report. Each has two membranes, and the inner one is folded into cristae that hold the protein complexes of the electron transport chain. Electrons stripped from food pass along that chain to oxygen, and the energy released pumps protons across the membrane; the resulting gradient drives ATP synthase, the rotary enzyme that assembles ATP. Mitochondrial DNA encodes only 37 genes; the nucleus supplies the rest of the proteins. How many a cell contains varies enormously by tissue, from very few in some cell types to thousands in heart muscle.
No routine blood test or consumer panel reads mitochondrial function. Research measures it in awkward ways: respirometry on a muscle biopsy, magnetic resonance spectroscopy timing how fast phosphocreatine is restored after exercise, enzyme markers such as citrate synthase activity, and mitochondrial DNA copy number in blood cells. These methods are not interchangeable, and what counts as normal shifts with the tissue sampled, the assay, and the person’s age and training status, so treat any single published cut-off with suspicion. The closest whole-body proxy you can actually obtain is VO₂max (maximal oxygen uptake), which reflects both oxygen delivery and how much of it working muscle can use.
Why it matters for longevity
Mitochondrial dysfunction sits on every published list of the hallmarks of aging. In older muscle, mitochondrial content and respiratory capacity are on average lower, damaged mitochondria are cleared less efficiently, and mutations in mitochondrial DNA accumulate. How much of that is aging and how much is decades of reduced activity is genuinely contested, because weeks of bed rest reproduce a similar pattern in young people. Rare inherited mitochondrial diseases show the severe end of the spectrum, hitting the most energy-hungry tissues first.
The older free radical theory held that electrons leaking from the chain generate reactive oxygen species, and that the resulting Oxidative stress accumulates until it drives aging. That story has not survived intact: large antioxidant supplement trials have not extended life, and low doses of the same signal appear to act as a useful training stimulus rather than only as damage. What remains well supported is an association — people with better aerobic and mitochondrial capacity have lower mortality and less frailty — not proof that repairing mitochondria would extend a life.
What changes it
Endurance exercise is the one lever with strong, repeatable human evidence. Training raises mitochondrial content and enzyme activity in the muscles being used, in older adults as well as young ones. Easy long sessions and hard intervals both produce the adaptation, largely by different routes, so the practical answer is a mix rather than a debate. Resistance training adds the muscle that houses them. Inactivity moves the number down faster than training moves it up, which makes not stopping the underrated part of the plan.
Supplements are where claims outrun data. Coenzyme Q10 carries electrons inside the chain and has real evidence in heart failure, but not as an anti-aging measure for healthy people. NAD precursors such as NMN and NR raise NAD+ in blood, with no trial showing slower aging. Urolithin A targets the recycling of damaged mitochondria and has improved muscle endurance markers in small studies, with lifespan effects unproven. The best evidence per dollar is the training, not the bottle.
Related reading
- VO2 Max: Why Aerobic Fitness Predicts Longevity
- How to Build a Training Program for Longevity
- Coenzyme Q10 and Longevity: An Evidence Review
- NMN: What the Research Actually Shows
Disclaimer. This article is for information only and does not replace medical advice. Talk to a qualified clinician before changing anything about your health.