Mitochondrial dysfunction symptoms: what your fatigue may and may not mean

Short answer

Mitochondrial dysfunction symptoms usually start with energy: deep tiredness that rest doesn't fix, low stamina, muscle weakness or pain, and slow recovery after effort. People with fatigue describe exactly this mix — low energy, mental and physical tiredness, reduced endurance and long recovery — and a review of 25 studies found signs of mitochondrial problems in several fatigue-linked conditions (2).

Mitochondrial dysfunction is not one disease. Inherited mitochondrial disease is rare — about 1 in 5,000 people — and usually affects several organs at once, such as muscles, brain, eyes, ears and heart. Much more often, mitochondria work less well because of another condition, such as diabetes, multiple sclerosis or ageing; doctors call this secondary mitochondrial dysfunction (1).

In ME/CFS and long COVID, studies do find energy-system changes — most clearly in muscle after effort — but no mitochondria drug or supplement has clearly beaten placebo yet. There is no simple home test, and no supplement has been shown to "fix" it. If your energy has dropped and won't come back, you're not imagining it — but the next step is a doctor's work-up for common, treatable causes, not a bottle of pills.

Note: this article is for general education and is not medical advice. Seizures, trouble breathing, fainting, or sudden weakness are emergencies: call 911 or your local emergency number. This guide is published by Welltory, which makes one of the apps mentioned. Welltory is a general wellness product: it helps you track and understand your data and does not diagnose or treat any condition.

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What is mitochondrial dysfunction?

Mitochondrial dysfunction means the tiny power stations inside your cells are not making energy as well as they should.

Think of each cell as a small town. Mitochondria are its power plants. They take fuel from food (sugar and fat) and oxygen from your breath and turn them into ATP — a molecule that works like a charged battery. Every muscle twitch, heartbeat and thought spends these batteries. Mitochondria produce about 90% of the body's energy (1).

When the power plants slow down, the town doesn't go dark all at once. It runs on a budget. Parts that use the most energy — muscles, brain, heart, nerves — feel the shortage first. That is why the symptoms are so often about stamina, thinking and recovery.

Two terms get mixed up online, so here they are side by side:

• Mitochondrial disease (also called primary mitochondrial disease) is a genetic condition. A change in DNA breaks part of the energy machinery from birth. It is rare and usually diagnosed by specialists with genetic tests (1).

• Secondary mitochondrial dysfunction is when mitochondria work less well because something else is going on — another illness, inflammation, inactivity, ageing. It is not inherited, and it is far more common (1).

Signs of mitochondrial dysfunction

The most common signs are about energy, muscles and recovery. Because mitochondria are in almost every cell, symptoms can show up anywhere, but these are the ones people notice first:

1. Fatigue that rest doesn't fix. Not ordinary end-of-day tiredness, but a heavy, whole-body drain.

2. Low stamina. Activities you used to do easily — stairs, a walk, a full workday — now use you up.

3. Slow recovery. It takes a day or more to bounce back from effort that used to be nothing (2).

4. Muscle weakness, cramps or pain, especially after use.

5. Brain fog. Trouble concentrating, finding words or keeping track of things.

6. Exercise intolerance. Feeling worse, not better, after exercise.

In inherited mitochondrial disease, the list is wider and more serious: poor growth in children, low muscle tone, vision or hearing loss, seizures, migraines, digestive and swallowing problems, breathing problems and fainting. Several organ systems are usually involved at the same time (1).

The honest catch: every symptom in the first list is also a symptom of anemia, thyroid problems, poor sleep, depression, sleep apnea, low vitamin levels and many other common conditions. The symptoms don't tell you where the energy problem is. Tests do.

Mitochondrial disease vs everyday fatigue

Based on Cleveland Clinic (1).

What causes mitochondrial dysfunction?

Mitochondrial dysfunction is caused either by inherited gene changes or, more often, by other conditions that strain or damage the cell's energy machinery.

• Genes. Inherited mitochondrial disease follows dominant or recessive patterns, or appears as a new mutation. Changes in mitochondrial DNA itself are passed down only through the mother (1).

• Other diseases. Alzheimer's disease, muscular dystrophy, type 1 diabetes, multiple sclerosis and cancer can all cause secondary mitochondrial dysfunction (1).

• Inactivity and ageing. Muscles that are used less tend to keep fewer and less active mitochondria. Older adults may have lower baseline mitochondrial function (6).

Mitochondrial dysfunction in ME/CFS and long COVID: what research shows

Is mitochondrial dysfunction real? Yes — but in ME/CFS and long COVID it is a piece of the puzzle, not a proven cause. Researchers test blood and cells in the lab, take small muscle samples (biopsies) and scan muscles during exercise — and these methods don't always agree.

Is ME/CFS a mitochondrial disease?

No. ME/CFS is not classified as a mitochondrial disease, but mitochondria may work differently as part of the illness. "Mitochondrial disease" means a genetic fault in the energy machinery. No such gene fault has been found to explain ME/CFS.

• The big review. A 2020 systematic review looked at 19 studies comparing people with ME/CFS to healthy controls. Four of five studies on how mitochondria use oxygen found differences, and both studies on coenzyme Q10 found lower levels. But results on ATP itself were split (lower in three studies, unchanged in three), and no study found disease-causing mitochondrial DNA. The authors concluded that ME/CFS is "not a primary mitochondrial disorder," although mitochondrial decline may happen as a consequence (3).

• A failed replication — and why it matters. An earlier small lab study (12 patients, 12 controls) reported that blood serum from people with ME/CFS changed how healthy muscle cells used oxygen. A larger repeat of the same experiment used serum from 67 people with ME/CFS and 53 healthy controls. This time, serum from people with ME/CFS and from healthy people "did not differentially affect" the cells' maximum oxygen use (25).

• No lab test, no approved drug. CDC states there is no cure or approved treatment for ME/CFS (28), and diagnosis is made from symptoms after other causes are ruled out (5).

What this means: the energy system in ME/CFS looks disturbed in many studies, but findings change from lab to lab and group to group. Mitochondrial dysfunction in chronic fatigue syndrome is a serious research lead, not a settled target. Read more in our guides to ME/CFS symptoms and chronic fatigue syndrome symptoms.

Does long COVID damage mitochondria?

Some studies point that way, especially in muscle, but "damage" is stronger than the evidence can prove for every person. The clearest long COVID mitochondria findings come from two kinds of muscle studies.

Muscle biopsies (Appelman, 2024). Researchers took small muscle samples from 25 people with long COVID and 21 people who had fully recovered from COVID, before and after a hard cycling test meant to trigger post-exertional malaise. At the start, the long COVID group had lower mitochondrial capacity and more fast-tiring muscle fibers. After the test, a mitochondrial enzyme marker dropped in the long COVID group but not in controls, and signs of muscle damage increased more in patients (4). The study was small and cannot prove cause.

Muscle energy scans (Finnigan, 2024). A special MRI scan called MR spectroscopy can watch muscle energy recover in real time after exercise. It tracks phosphocreatine — the muscle's quick-release energy reserve, like a small backup battery. In 41 people with post-COVID condition and 29 healthy controls, this backup battery took longer to recharge after exercise: about 92.5 seconds versus 51.9 seconds. Estimated mitochondrial capacity was also lower. Two honest caveats: the post-COVID group was older on average, and the scan results did not match how tired people said they felt (22).

Put together: after COVID, some people's muscles seem to refill energy more slowly, and hard effort can make that worse. Nobody yet knows whether this is permanent or how much of the fatigue it explains. Our guide to long COVID symptoms covers the wider picture.

Mitochondria and fatigue: why effort can backfire

When mitochondria can't keep up, muscles lean on faster, less efficient ways of making energy, and recovery takes longer.

In the long COVID biopsy study, patients had lower peak oxygen uptake and lower power on the bike than controls, and that gap was not explained by the heart or lungs — it pointed to the muscles themselves (4).

That is why "just do more" is the wrong advice for some people. In healthy muscle, regular exercise builds more and better mitochondria. In people with post-exertional malaise (PEM), the same logic can fail. PEM is symptoms that get worse after physical, mental or emotional effort (5). In ME/CFS, symptoms typically worsen 12 to 48 hours after activity, and PEM can last for days or even weeks (27). CDC is direct about it: exercise is not a cure for ME/CFS (27).

The two-day exercise test: what it shows — and who it doesn't fit

On a two-day exercise test, many people with ME/CFS do worse on day 2, but not everyone does.

In a 2-day CPET (cardiopulmonary exercise test), you ride an exercise bike while a mask measures how much oxygen your body uses. Then you repeat the test 24 hours later. Healthy people usually score about the same both days.

• Keller, 2024 — a drop on day 2. In the largest study so far, 84 people with ME/CFS and 71 inactive controls did two tests 24 hours apart. People with ME/CFS "failed to reproduce" their day-1 results; controls did reproduce them. In a matched group of 55 patient–control pairs, people with ME/CFS showed a 6% drop in peak oxygen uptake and a 6.7% drop in oxygen uptake at the threshold where the body switches to less efficient energy pathways (20).

• Mancini, 2026 — no drop. A different team tested 58 people with ME/CFS and 25 inactive controls the same way and found no significant change on day 2 in either group. The authors concluded the data "do not support using the 2-day CPET protocol to define PEM or disability" (21). Their study only included people well enough to finish two maximum-effort tests, and it did not measure PEM directly.

So the day-2 drop is real for many people, but not universal. Either way, the practical lesson holds: if you have PEM, a "do more to build your mitochondria" plan can trigger a crash. Pacing — staying inside your energy envelope — is the safer path, which we explain in pacing with chronic illness and what the energy envelope is. Our guide to post-exertional malaise explains the crash itself.

Is it really the mitochondria? Other explanations researchers are testing

A muscle can look "low on energy" because its power plants are weak — or because not enough blood and oxygen reach it in the first place. Mitochondria are the last step in a long oxygen delivery chain.

• Blood flow to the brain when upright. In a tilt-table study of 429 people with ME/CFS and 44 healthy controls, blood flow to the brain fell by 26% in ME/CFS at the end of the test, versus 7% in controls. Even in patients whose heart rate and blood pressure looked normal, it fell by 24% (23).

• Filling and oxygen use during exercise. In invasive exercise tests of 160 people with ME/CFS and 36 controls, patients reached about 80% of their predicted peak oxygen uptake versus about 101% in controls. Many had low filling pressure in the heart, and some used less of the oxygen their blood carried (24).

So the better question may be "Where is the energy chain breaking for this person?" — blood return, oxygen use, the muscle's power plants, or several at once.

How to test for mitochondrial dysfunction

There is no single blood test that confirms mitochondrial dysfunction. Doctors build the picture step by step (1):

1. History and family history. When symptoms started, what makes them worse, and whether relatives have similar problems.

2. Physical and neurological exam. Muscle strength, reflexes, eyes, hearing.

3. Blood and urine metabolic tests. These look for signs that the body is struggling to burn fuel cleanly.

4. Genetic testing. DNA tests can find known mitochondrial disease genes.

5. Other tests, depending on symptoms. Imaging, eye and hearing tests, heart tests, brain-wave tests.

6. Muscle or tissue biopsy in some cases.

Because no single lab test confirms it, referral to a specialist is important when inherited disease is suspected (1).

What usually comes first: for most adults with new, lasting fatigue, a doctor will check common causes before anything mitochondrial — blood count for anemia, thyroid, blood sugar, iron, vitamin B12 and vitamin D, kidney and liver function, and screening for sleep apnea and depression. Our guide to what fatigue is walks through these.

How to fix mitochondrial dysfunction — and can it be reversed?

For inherited mitochondrial disease, there is no cure; treatment manages symptoms and prevents complications (1). For secondary dysfunction, the main lever is treating whatever is behind it.

What doctors may use, depending on the situation (1):

• Treating the underlying condition — for example, managing diabetes or recovering from a viral illness.

• Supplements under medical supervision. In diagnosed mitochondrial disease, doctors sometimes use riboflavin, coenzyme Q10 or carnitine. These are prescribed for specific cases and discussed with a clinician, not a general energy fix.

• Avoiding triggers that cause flare-ups: extreme temperatures, skipped meals, poor sleep and stress.

Can it be reversed? It depends on the cause. Secondary dysfunction can improve when the underlying problem improves. In healthy people, trials of training show that muscle mitochondria can adapt — studies of resistance training, for example, generally report better mitochondrial respiration in muscle fibers after 10–12 weeks, though results on mitochondrial amount are mixed (6). In ME/CFS and long COVID, no treatment has yet been shown to reliably reverse the mitochondrial changes — and because of PEM, exercise is not the shortcut it is for healthy people (see above).

What's been tested in trials: CoQ10, oxaloacetate, NAD+, elamipretide

Several "energy" supplements and drugs have been tested in ME/CFS and long COVID; so far, none has clearly and repeatedly beaten placebo on the main result the trial was designed to measure. We deliberately don't list doses: any supplement is something to discuss with your doctor first.

Trials checked November 9, 2026.

What the table teaches:

1. "People felt better" is not the same as "it beat placebo." In fatigue illnesses, scores often improve in both groups, as they did in the CoQ10 long COVID trial (12).

2. Moving a lab number doesn't guarantee you'll feel better. Nicotinamide riboside raised NAD+, yet people did not feel better than on placebo (17).

3. Check who paid. Both oxaloacetate trials were funded by the company commercializing it; that is a reason to wait for independent repeats (15, 16).

Is there a drug for mitochondrial dysfunction in ME/CFS or long COVID?

Not yet. No drug is approved to treat mitochondrial dysfunction in ME/CFS or long COVID. CDC states there is no cure or approved treatment for ME/CFS (28), and the long COVID trials above have not produced a proven option. For what is being tried in long COVID care more broadly, see our guide to long COVID treatment.

What is elamipretide — and is it approved for ME/CFS?

Elamipretide is a mitochondria-targeted drug approved only for Barth syndrome, a rare inherited mitochondrial disease. On September 19, 2025, the FDA granted accelerated approval to elamipretide (brand name Forzinity) as the first treatment for Barth syndrome, in patients weighing at least 30 kg. "Accelerated" means the approval rests on an early measure — here, knee muscle strength — and the maker must run a further placebo-controlled trial to confirm real patient benefit (19). That approval does not cover ME/CFS, long COVID, fatigue or PEM, and we found no controlled trial of elamipretide in these conditions.

What this means for your energy — and what you can see in your data

No app or watch can measure your mitochondria, ATP or lactate. What you can see are the downstream signals of how your body is coping:

• Resting heart rate. When the body is under strain — after overexertion, during illness, after poor sleep — resting heart rate often rises by a few beats above your usual level.

• Heart rate variability (HRV). HRV reflects how flexibly your nervous system is adjusting. A run of lower-than-usual mornings often lines up with stress, poor recovery or getting ill.

• Sleep. Short or broken sleep shows up the next day as lower energy and a higher resting heart rate.

• Your own notes. How you feel on a 1–10 scale, what you did yesterday, and when symptoms started.

These signals don't diagnose anything, and they can't tell you whether mitochondria are involved. But tracked over weeks, they help you see your pattern: which kind of day tends to come before a bad one, and how long recovery usually takes. Because PEM often arrives 12 to 48 hours late, looking back two days — not just at today — is what makes the pattern visible. People with ME/CFS often use exactly this to pace — see our guides to morning HRV and pacing and heart rate pacing.

Common mistakes people make with this diagnosis

• Self-diagnosing from a symptom checklist. The symptoms overlap with anemia, thyroid disease and sleep apnea, which are common and treatable.

• Buying "mitochondria" supplement stacks first. They are expensive, mostly untested for this use, and can delay the work-up that matters.

• Changing five things at once. Then you can't tell what helped or what caused a crash.

• Pushing harder to "train the mitochondria" when you have post-exertional malaise.

• Treating one bad week as the full story. Patterns over weeks tell you more than any single day.

• Ignoring red flags like fainting, seizures, or new vision or hearing loss.

Living with low energy: the questions people ask next

How do I know if I have mitochondrial dysfunction?

You can't know from symptoms alone. If you have fatigue that rest doesn't fix, low stamina and slow recovery, start with a doctor's work-up for common causes. If several organ systems are involved, or relatives have similar problems, ask about a referral to a specialist in mitochondrial or metabolic disease (1).

Can you test your mitochondria at home?

Not in a way that diagnoses anything. Research labs can measure how mitochondria use oxygen, but there is no validated mitochondrial dysfunction test you can buy that tells you whether you have ME/CFS, long COVID or a mitochondrial disease.

One commercially available "cellular energy" blood test was checked by independent researchers in people with ME/CFS and healthy controls. Their verdict: it "does not have the reliability and reproducibility required of a diagnostic test" (26). Direct-to-consumer kits are not how mitochondrial disease is diagnosed. Genetic testing is different: it makes sense when a doctor suspects inherited mitochondrial disease from your symptoms, exam and family history.

Does CoQ10 help long COVID fatigue?

The best placebo-controlled trial says no. In 121 people with post-COVID condition, CoQ10 did not reduce the number or severity of symptoms more than placebo; the authors concluded it "does not appear to significantly reduce" them (12). For CoQ10 and chronic fatigue syndrome, the largest trial combined CoQ10 with NADH and did not show a clear advantage over placebo either (13). CoQ10 can interact with some medicines, so discuss it with your doctor; see also CoQ10 and statins and supplement–drug interactions.

What about oxaloacetate for CFS and long COVID?

The evidence is early and mixed. In ME/CFS, the comparison with control was only a trend; in long COVID, the main fatigue score did not differ from control (see the trials table above). Both trials were funded by the company selling it.

Will there be a mitochondria pill?

Probably not soon, and probably not one pill for everyone. Research is moving toward sorting people into groups — by blood flow, immune signaling or muscle energy — and testing treatments in the group most likely to respond.

Before you blame yourself

When energy disappears, many people decide they are lazy, weak or "not trying hard enough". Before you blame yourself, look at your data. Fatigue usually has a cause you can see: nights of short sleep, a resting heart rate that has crept up, a week where you did more than your body could recover from. Pick one lever — a steadier bedtime, or keeping activity below the level that triggers a crash — and watch it for one to two weeks. If your energy still doesn't come back, that isn't a personal failure. It's information to take to your doctor.

When to see a doctor

See a doctor if fatigue lasts more than a few weeks, doesn't improve with rest, or stops you from doing things you used to do. Also book an appointment if you notice muscle weakness, worsening exercise tolerance, new problems with vision or hearing, or symptoms that get worse after effort. ME/CFS is diagnosed when reduced ability to do your usual activities lasts more than 6 months, with post-exertional malaise and unrefreshing sleep (5).

If you are thinking about any supplement, discuss it with your doctor first, especially if you take regular medicines, are pregnant or have kidney or liver disease.

Call 911 or your local emergency number for a seizure, trouble breathing, fainting, or sudden weakness or confusion (1). Other warning signs of a medical emergency include chest pain or discomfort, sudden severe pain, and sudden dizziness or vision changes (29). These need same-day care, not a supplement experiment.

How to bring this up with your doctor

What to ask for, by name. "Can we check for common causes of fatigue — blood count, thyroid, iron, B12, blood sugar?" If those are normal: "Could this be post-exertional malaise or ME/CFS?" If several organs are involved or there is a family history: "Should I see a specialist in mitochondrial or metabolic disease?"

What to bring. A two- to four-week log of how you felt each day, what you did, how you slept, and any resting heart rate or HRV trend you track. A list of all medicines and supplements.

What to say, out loud. "I used to be able to do [activity]. Now it takes me [time] to recover, and I feel worse the day after effort."

If you're thinking about a supplement. "I've read about CoQ10 / NAD+ / oxaloacetate. Is it safe with my other medicines, what would we watch, and when would we stop if it doesn't help?"

If you're told it's stress or deconditioning. Ask: "If I try to exercise more, my symptoms get worse for days. Can we rule out post-exertional malaise before I increase activity?"

How Welltory helps — and what it cannot do

The limits first. Welltory is a general wellness product, not a medical device. It does not measure mitochondria, ATP or lactate, and it does not diagnose mitochondrial disease, ME/CFS or any other condition.

What it can do is help you see your own energy pattern over time:

A daily snapshot with your phone camera. You can take a spot HRV and heart rate reading with your phone camera and flash — a short, deliberate measurement, not continuous monitoring (camera measurements). Measure at the same time each morning for comparable results (accurate HRV measurements).

Your watch or ring, in one place. You can connect a wearable or health platform as a data source so sleep, heart rate and activity sit next to your morning readings (data sources).

Tag what happened. When Welltory asks "What happened?" after a stress or recovery episode, you can tag "long walk", "bad night" or "crash" and later see what tends to come before your harder days (My Patterns).

A record for your doctor. From the web app you can export your data as CSV (export guide).

Where you can learn this with other people. Welltory runs a paid, moderated community called Energy Lab for women aged 18 to 65 living with ME/CFS, long COVID, fibromyalgia, POTS, MCAS and similar. Members get a personal pacing strategy built on their own data, a community of women with similar symptoms, and a medical board that explains what is happening in the body. It is education and peer support, not medical care, and it does not replace your clinician. Membership renews automatically; you can cancel online at any time, and your first purchase has a 14-day money-back guarantee. Read what the community is, who it is for and what it costs.

How we made it

We based this article on Cleveland Clinic's overview of mitochondrial diseases, a literature review on mitochondrial dysfunction and fatigue, a systematic review of mitochondrial abnormalities in ME/CFS, muscle-biopsy and muscle-scan studies in long COVID, two-day exercise-test studies in ME/CFS, studies of blood flow and oxygen delivery, the published results of supplement and drug trials, the FDA announcement on elamipretide, and CDC clinical pages on ME/CFS. We checked each study and regulatory number in this article against its source on November 9, 2026. Search questions came from what people in the United States most often ask about mitochondrial dysfunction, ME/CFS and long COVID. For the product section, we checked every function against the Welltory Help Center on November 9, 2026.

Made with AI tools, then edited and fact-checked by the Welltory team. See our Editorial & AI policy.

Jane Smorodnikova, co-founder of Welltory, built the methodology behind how we read physiological data.

Written by Mariia Podobed and Tatsiana Yashyna.

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