The Study
ACE-031, a soluble activin type IIB receptor, increases muscle mass and strength in the common marmoset (Callithrix jacchus)
This study tested a medicine on monkeys and found that their muscles got bigger and stronger. But that doesn't mean it will work the same way in people—it's like saying a toy car works on a track, so a real car will too. We need to test it in humans to know for sure.
Analysis score
Maximum 90 for a randomized controlled trial.
Where the score came from
Scientists gave a special protein to monkeys to block signals that stop muscles from growing. They wanted to see if it could help people with muscle-wasting diseases.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 516 / 100
Quality score
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
Key takeaways
Summary
Based on the study abstract and findings.
- 1This suggests the drug could help humans gain stronger, healthier muscle without side effects like fat gain or losing endurance — but safety in humans is still a concern.
- 2Monkeys got 20% bigger fast-twitch muscle fibers, 34% bigger slow-twitch fibers, and their muscles produced 20–30% more force per unit of size — all without gaining fat or changing fiber types.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
PLOS One
Year
2026
Authors
Samuel M. Cadena, S. Bogdanovich, T. Khurana, Abigail Pullen, R. Pearsall, Elizabeth Curran, Ryan Faucette, Joan Lane, J. Seehra, Jennifer L. Lachey, Alan D. Mizener, E. Pistilli
Related Content
Claims (6)
Myostatin-inhibiting antibodies increase muscle mass in animals by blocking biological signals that normally restrict muscle growth.
In common marmosets, ACE-031 treatment increases lean body mass while fat mass remains unchanged, demonstrating that the effect is specific to muscle tissue and not due to overall weight gain.
In healthy adult common marmosets, weekly injections of ACE-031 for 14 weeks result in increased lean body mass and larger type I and type II muscle fibers in the biceps brachii.
In common marmosets treated with ACE-031 for 14 weeks, the percentage of type I muscle fibers in the biceps brachii remains at 16%, and the ratio of type I to type II fibers does not change.
In common marmosets, 14 weeks of ACE-031 treatment increases the force generated per unit of muscle mass in the extensor digitorum longus muscle by 20–30%, without changing the total force output or the proportion of muscle fiber types.
In common marmosets given ACE-031 for 14 weeks, no harmful changes were observed in blood chemistry or tissue structure, even though similar treatment in humans caused blood vessel problems, suggesting the two species respond differently to this compound.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.