Exerkines: the molecules exercise releases, explained
Your body doesn't just burn calories when you move — it sends a cascade of chemical messages.
TL;DR
- Exerkines are signaling molecules (in plain English: chemical messages) that muscles and other tissues release during exercise.
- Klotho and irisin are two of the most studied; MOTS-c is a mitochondrial-derived peptide that also rises with movement.
- Exercise is the only well-supported way to raise these molecules — injectable versions are still research-stage.
What it is
Exerkines are molecules your body makes and releases in response to physical movement. Think of them as postcards your muscles send to other organs while you work out. The postcard says: "We're moving — time to adapt." Klotho (a protein associated with cellular aging and kidney function) and irisin (a protein secreted by muscle during contraction) are among the most studied. A third, MOTS-c (a mitochondrial-derived peptide, meaning a small signaling protein encoded inside the mitochondria — your cells' energy generators), has drawn research interest as an exercise-responsive molecule. Scientists now use "exerkines" as the umbrella term for all of these signals (Hackney & Lane, 2024).
How it works
Picture exercise as someone pushing a button on a factory intercom. When the button is pressed, a series of announcements goes out across the building. Klotho goes up in the bloodstream after aerobic effort. A 2022 systematic review and meta-analysis found that exercise consistently increased circulating klotho levels across studies (Ponce-González et al., 2022). Irisin is released when muscle contracts and appears to cross into the brain in animal studies, where it has been linked to learning and memory. MOTS-c rises in plasma and muscle tissue during exercise and travels to the cell nucleus to adjust gene activity involved in stress adaptation (Lu et al., 2022).
Who asks about it
People come to this topic after hearing "exerkine" on a longevity podcast and wondering whether it means there is a pill or injection that could replicate what exercise does. That is the right instinct to question. Many also ask whether klotho supplements they found online are legitimate. (Short answer: the protein breaks down in the gut — those products are not delivering what they promise.)
What the research says
The research on exerkines is real, early, and largely in animals. Klotho studies in humans show consistent increases with aerobic exercise. Irisin research is promising in mice but human data is still limited and mixed. MOTS-c studies in rodents show improvements in metabolic health and exercise capacity; early human data is emerging but not yet definitive. No exerkine has a proven, approved therapeutic application as an injectable for general wellness.
What to know before considering it
Exercise remains the only intervention with a strong, consistent evidence base for raising these molecules in humans. MOTS-c as an injectable peptide is Category 2 under FDA rules — not currently available from 503A compounding pharmacies. Anyone interested in peptide therapies needs a licensed clinician's evaluation, a valid prescription, and a state-licensed pharmacy. No supplement product delivers meaningful doses of klotho or irisin.
The Halftime POV
The exerkine story is one of the best arguments for consistent movement we know of. Your body has a built-in molecular signaling network that responds to exercise — and researchers are still mapping how it works. We will follow the science on injectable peptides like MOTS-c as the regulatory picture becomes clearer. In the meantime, the most effective exerkine protocol is still the one that gets you moving.
Related reading:
- VO2 max explained: what this longevity metric measures
- Zone 2 training explained: why this pace matters
- NAD+ mechanism explained
- The hallmarks of aging, explained
FAQ
Q: What are exerkines? A: Exerkines are signaling molecules — chemical messages — that your muscles and other tissues release during and after exercise. They travel through the bloodstream and tell other organs to adapt. Klotho, irisin, and MOTS-c are among the most studied.
Q: What do klotho and irisin do? A: Klotho is a protein associated with cellular aging and kidney health that rises after aerobic exercise. Irisin is a protein released by muscle during movement that has been linked to brain and metabolic health in animal studies. Both are naturally produced by the body — you cannot meaningfully supplement them.
Q: Can you take exerkines as a supplement? A: Not in any meaningful way right now. Klotho and irisin are proteins — they break down in the digestive tract and are not available as oral supplements. MOTS-c is a researched mitochondrial-derived peptide, but injectable versions are currently classified as Category 2 by the FDA and are not available from 503A compounding pharmacies.
Q: Is MOTS-c FDA-approved? A: No. MOTS-c is a Category 2 peptide, meaning it is not currently available from 503A compounding pharmacies. A February 2026 HHS announcement proposed returning certain peptides to Category 1 status, but a formal FDA Federal Register notice is still required before pharmacy access changes.
Disclaimer
As of 2027-01-27, several peptides discussed in this article — including MOTS-c — are classified by the FDA as Category 2, which means they are not currently available from 503A compounding pharmacies. A February 2026 HHS announcement proposed returning these peptides to Category 1 pending formal FDA Federal Register notice. This article is educational and is not medical advice. Halftime Health only prescribes through licensed clinicians in states where our partner physicians are credentialed.
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Sources
- Hackney AC, Lane AR, "'Exerkines': A Comprehensive Term for the Factors Produced in Response to Exercise," Sports Medicine (2024)
- Ponce-González JG et al., "A systematic review and meta-analysis demonstrating Klotho as an emerging exerkine," Scientific Reports (2022)
- Lu H et al., "Exercise, Mitohormesis, and Mitochondrial ORF of the 12S rRNA Type-C (MOTS-c)," Antioxidants (2022)
Frequently asked questions
What are exerkines?
Exerkines are signaling molecules — chemical messages — that your muscles and other tissues release during and after exercise. They travel through the bloodstream and tell other organs to adapt. Klotho, irisin, and MOTS-c are among the most studied.
What do klotho and irisin do?
Klotho is a protein associated with cellular aging and kidney health that rises after aerobic exercise. Irisin is a protein released by muscle during movement that has been linked to brain and metabolic health in animal studies. Both are naturally produced by the body — you cannot meaningfully supplement them.
Can you take exerkines as a supplement?
Not in any meaningful way right now. Klotho and irisin are proteins — they break down in the digestive tract and are not available as oral supplements. MOTS-c is a researched mitochondrial-derived peptide, but injectable versions are currently classified as Category 2 by the FDA and are not available from 503A compounding pharmacies.
Is MOTS-c FDA-approved?
No. MOTS-c is a Category 2 peptide, meaning it is not currently available from 503A compounding pharmacies. A February 2026 HHS announcement proposed returning certain peptides to Category 1 status, but a formal FDA Federal Register notice is still required before pharmacy access changes.
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