Poor Exercise Tolerance? Support Your Stamina and Energy

Reviewed by SOMA HEALTH's Medical Research Team

If a flight of stairs leaves you breathing harder than it used to, or a brisk walk feels like a workout, you are noticing something real. Exercise tolerance, the amount of physical effort you can sustain comfortably, is not fixed. It reflects how well your heart, lungs, blood vessels and muscle cells deliver and use energy. This guide explains the biology of feeling winded, what the current human research on Urolithin A actually shows, and where the science is still early, so you can make a calm, informed decision.

First, a note that matters

Getting winded or fatigued more easily can simply reflect deconditioning after a sedentary stretch. But it can also be an early sign of something that deserves medical attention, such as a heart, lung, thyroid or blood condition, sleep-disordered breathing, or anemia. This page is educational and covers structure and function support only. It is not a treatment for any medical condition. If your exercise tolerance has dropped noticeably, if you feel breathless at rest, or if you have chest discomfort, dizziness or swelling, please see your doctor before starting any new routine or supplement.

Why exercise capacity changes

Every muscle contraction is paid for in a molecule called ATP, and ATP is produced largely inside mitochondria, the small structures that act as your cells' power plants. When you exercise, muscle demands a steady, high output of ATP. Two things determine whether you can keep going: how efficiently oxygen and fuel reach the muscle, and how well the mitochondria inside those muscle fibers convert that fuel into usable energy.

With age and inactivity, both sides can slip. Research in human skeletal muscle has documented declines in mitochondrial density and function across the adult lifespan, alongside a well-known fall in aerobic capacity (VO2 max). Fewer and less efficient mitochondria mean the body leans harder on anaerobic pathways sooner, which is part of why effort that once felt easy now leaves you gasping. Just as important, older or damaged mitochondria are not always cleared and replaced as briskly as they once were, so the cellular workforce ages in place.

Where Urolithin A enters the picture

Urolithin A (UA) is a postbiotic, a compound your gut bacteria make when they break down ellagitannins from pomegranate, walnuts and certain berries. Not everyone's microbiome produces meaningful amounts, which is one reason a standardized supplement is used in research. UA's most-studied property is that it supports mitophagy, the housekeeping process that recycles worn-out mitochondria so healthier ones can take their place. In principle, better mitochondrial quality control is relevant to anyone whose energy and endurance have faded, which is why UA has been studied specifically in the context of muscle and physical performance.

What the human research shows

Here the distinction between proven human data and early preclinical work matters, and we keep them separate.

Established human safety and biology

The first-in-human study, Andreux and colleagues (Nature Metabolism, 2019), found Urolithin A was safe and well tolerated at doses up to 1,000 mg per day and produced a measurable mitochondrial gene-expression signature in skeletal muscle. That established both a safety envelope and biological plausibility in people, not just cells.

Newer human trials on strength and endurance

Singh and colleagues (Cell Reports Medicine, 2022) studied middle-aged adults over four months, testing 500 mg and 1,000 mg daily arms, and reported improvements in muscle strength and measures of exercise performance. Liu, D'Amico and colleagues (JAMA Network Open, 2022) worked with older adults over roughly four months and observed improvements in muscle endurance. A 2024 randomized trial in the Journal of the International Society of Sports Nutrition ran eight weeks in resistance-trained men, extending the question into an already-fit population, and a 2025 trial in distance runners looked at UA in endurance athletes. Separately, a 2025 randomized study in Nature Aging found that a roughly 28-day course supported immune-cell mitochondrial health in midlife adults, part of the emerging conversation around inflammaging.

Taken together, these are genuine human trials pointing in a consistent direction for muscle function and cellular energy. They are also modest in size and duration. A 2024 systematic review in Ageing Research Reviews on targeting aging with Urolithin A in humans concluded, fairly, that the evidence is still emerging. Honest framing is part of the point: UA is a supportive tool with a growing but not yet definitive human evidence base, not a shortcut around training.

Preclinical work, labeled as such

Much of the mechanistic story comes from animal and cell studies, which suggest possibilities rather than prove human outcomes. Ryu and colleagues (Nature Medicine, 2016) showed UA induced mitophagy, extended lifespan in the worm C. elegans, and improved muscle measures in rodents. D'Amico and colleagues (Aging Cell, 2022) explored joint and cartilage effects in osteoarthritis models. Early or preclinical research is also exploring UA's role in skin, gut, brain and heart biology. These findings are encouraging context, but they are not evidence of benefit in humans and should not be read that way.

Practical ways to support your stamina

Supplements sit on top of fundamentals, never in place of them. The most reliable way to raise exercise tolerance is to gradually and consistently ask more of your cardiovascular system: zone-two aerobic work most days, a little resistance training to preserve muscle, adequate protein, sleep and hydration. If you choose to add Urolithin A, think of it as support for the cellular machinery that training is trying to build.

For dosing specifics, the human trials used 500 to 1,000 mg per day, with 1,000 mg as the top studied amount. You can read more in our Urolithin A dosage guide and about tolerability in our overview of Urolithin A side effects. To understand the underlying biology, see what mitophagy is. For the bigger picture, start with our complete Urolithin A guide, compare formats in the best Urolithin A gummies, and see how UA relates to Urolithin A for energy.

Consistency matters more than any single dose. UA works through slow, ongoing cellular housekeeping, so benefits, where they occur, build over weeks rather than in a single session. Set a realistic expectation and give any change a full trial period alongside steady training.

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This guide is educational and is not a substitute for advice from a qualified healthcare provider.