The Study
Small muscle mass exercise enhances muscular adaptations? Effects of unilateral and bilateral biceps curl on maximum strength and muscle size changes.
This study is like a fair race between two groups of girls doing different kinds of bicep curls. One group used both arms at once, the other used one arm at a time. After 8 weeks, the one-arm group got stronger in the arm they trained, but both groups got about the same muscle size. So we can say: 'For these girls, using one arm at a time made that arm stronger — but didn’t make the muscle bigger than using both arms.'
Analysis score
Maximum 90 for a randomized controlled trial.
Where the score came from
People who trained one arm at a time got stronger in that arm, but not in the other arm or in both arms together. Both training styles made muscles about the same size.
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 561 / 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.
- 1Yes — if you want to get stronger in one arm, train it alone.
- 2But if you want overall strength or bigger arms, both methods work equally well.
- 3Right arm got 0.75 kg stronger with one-arm curls.
- 4Muscle size didn't change between groups.
- 5Left arm didn't get stronger from right-arm training.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
European journal of applied physiology
Year
2025
Authors
Witalo Kassiano, Ian Tricoli, Felipe Gomes, Vanessa Santos-Melo, Ingrid Manske, Gabriel Kunevaliki, Felipe Lisboa, Alexandre Miguel, Aline Prado, Natã Stavinski, Edilson S. Cyrino
Related Content
Claims (6)
Training one arm at a time doesn’t make you stronger when lifting with both arms together — your total strength gain is the same as training both arms at once.
Whether you lift weights with one arm or both at the same time, your biceps grow about the same amount after 8 weeks of training.
Doing bicep curls with one arm makes that arm stronger for one-arm curls, but doesn’t make you stronger for two-arm curls or the other arm.
Doing bicep curls one arm at a time makes your right arm stronger than doing them with both arms together, but doesn't make your biceps bigger than using both arms.
Training your right arm alone makes your right arm stronger, but doesn’t help your left arm get stronger — the benefit stays on the side you trained.
For small muscle groups, unilateral and bilateral resistance training produce equivalent hypertrophic adaptations when volume and effort are matched.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.