In untrained young women, doing bicep curls with one arm at a time may lead to slightly stronger gains in that arm compared to using both arms together, but does not result in larger muscle growth,...

We analyzed one assertion on this topic and found it supports the idea that in untrained young women, doing bicep curls with one arm at a time may lead to slightly greater strength gains in that arm compared to using both arms together, without causing larger muscle thickness [1]. This suggests the nervous system may adapt more efficiently to unilateral training, helping the arm produce more force without needing bigger muscles. We did not find any evidence contradicting this observation. The difference in strength gains was modest, and muscle size remained unchanged in both training styles. What we’ve found so far points to a possible advantage in neural adaptation with single-arm training, but we cannot say whether this applies to trained women, men, or older adults. The evidence is limited to one group — untrained young women — and only one study was reviewed. We don’t know how long the training lasted, how often it was done, or whether the strength gains lasted beyond the study period. For someone just starting out, this might mean switching between one-arm and two-arm curls could help build strength without adding bulk, but more research is needed to confirm this pattern. For now, if you’re new to lifting and want to focus on strength without noticeable muscle growth, trying unilateral curls could be worth exploring.