A systematic review published in Physiological International on 25 August 2026 asked a narrow question: does physical exercise raise the circulating level of mitochondria-derived peptides, MOTS-c and humanin among them.

The search across PubMed, Scopus, Web of Science and ScienceDirect returned 435 records for the years 2016 to 2025. After PRISMA screening, nine made it into the analysis.

Most of those nine reported a trend toward increased levels after exercise. The authors then say, in the results section rather than buried in the limitations, that the findings should be interpreted with caution given the small number of studies and the variation in design, subject characteristics and exercise protocols.

A framing note. Peptra Labs supplies MOTS-c as reference material for laboratory research only, and nothing here is guidance about exercise, training or human use of any compound.

Why the MOTS-c question exists at all

The premise is a 2021 paper in Nature Communications that identified MOTS-c as an exercise-induced regulator of age-dependent physical decline and muscle homeostasis. That is the study the whole field points back to, and it is the reason anyone is measuring this peptide in blood before and after a treadmill test.

Mitochondria-derived peptides are a small family, encoded inside the mitochondrial genome rather than the nuclear one. Humanin was the first described. MOTS-c is the one with the metabolic literature. Both are proposed to act as stress-responsive signals, and exercise is the cleanest physiological stressor available for testing that.

We have covered the family twice before, once through the microprotein literature it belongs to and once through its identification as a host defence peptide with antibacterial and immune functions beyond the metabolic role.

What 435 to 9 tells you

The screening ratio is the most useful number in this paper, and it is not a criticism of the authors.

Four databases, ten years, and a search designed to find studies about mitochondria-derived peptides and exercise, and nine studies met the inclusion criteria. That is roughly one study a year, worldwide, on a question that has been called promising since 2021.

It also puts a ceiling on what any conclusion can be. Nine studies cannot support subgroup claims about age, sex, training status or exercise modality, and they cannot separate acute response from chronic adaptation. The authors say the variation in exercise protocols alone limits comparison, which is the polite way of saying the nine studies are not measuring the same thing.

What “a trend toward increased levels” means

The phrase is doing careful work and deserves unpacking.

A trend toward increase is not the same as a statistically significant increase, and it is certainly not the same as a pooled effect size. A systematic review that stops at describing direction, without meta-analysing magnitude, has usually done so because the underlying studies are too heterogeneous to pool. That is a defensible choice and it is also an admission.

What the review can support is this: when people exercise, the measured level of these peptides more often goes up than down. What it cannot support is how much, in whom, after what, or whether any of it matters downstream.

The measurement problem nobody has solved

There is a difficulty underneath this literature that the exercise framing makes unusually visible.

A circulating level is not a mechanism. If MOTS-c rises after exercise, the rise could reflect increased production, reduced clearance, release from damaged tissue, or a shift in what fraction is detectable by the assay being used. Each of those means something different, and a blood draw before and after a session cannot distinguish them.

This is the same objection the critical care review raised last week from a completely different direction. We covered a review of the same peptide in septic cardiomyopathy whose authors listed biomarker specificity as their first named limitation, on the grounds that a marker which moves in sepsis, in exercise, in ageing and in metabolic disease is not specific to any of them.

Put those two papers side by side and the tension is clean. The exercise literature treats a rise in MOTS-c as evidence that something good is happening. The critical care literature treats a rise as possibly just a severity signal. Both are reading the same measurement.

Where this sits against the catalogue

Exercise physiology is one of the few places where a research peptide and a small molecule are chasing the same endpoint from opposite ends.

SLU-PP-332 is a pan-agonist of the estrogen-related receptors, described in the literature as an exercise mimetic because it switches on transcriptional programmes normally activated by endurance training. A 2026 paper in the International Journal of Biological Macromolecules reports chemical optimisation of the molecule and uses the analogues to probe how that receptor family signals.

The two approaches invert each other. One asks what exercise does to an endogenous peptide. The other asks whether a synthetic compound can produce the transcriptional consequences of exercise without the exercise. Neither has clinical outcome data, and both are supplied for laboratory work only.

None of this is a claim about what either compound does. The published record for both is preclinical, and in the case of the exercise question it is nine studies deep.

For laboratories working with these compounds, our European research buyer guide covers procurement and documentation, everything is supplied on a research use only basis, and our ranking of the most-studied research peptides counts papers rather than claims.

References

The products referenced on this site are supplied for laboratory research use only. They are not medicines and are not intended for human or veterinary use. This article summarises published research for informational purposes and is not medical advice. Statements about third-party studies belong to their authors.

author-avatar

About Peptra Labs Research

The Peptra Labs research desk follows peptide science: new peer-reviewed studies, EU and US regulatory decisions, and clinical trial results. Every article cites its primary sources. All compounds discussed are for laboratory research use only.

Newer
GLP-1 Below BMI 27: Benefit With Little Weight to Lose
Back to list
Older Semaglutide vs Tirzepatide in FAERS: 192,791 US Reports

Related Posts