In untrained young women, doing biceps curls with one arm or both arms at the same time leads to similar increases in biceps muscle thickness after 8 weeks, indicating that the total amount of work...

We analyzed two assertions about unilateral and bilateral biceps curls in untrained women, and both point to similar outcomes. What we’ve found so far suggests that whether a woman performs biceps curls with one arm at a time or both arms together, her biceps muscle thickness increases by about the same amount after eight weeks of training [1]. This appears to be because the total amount of weight lifted and the number of repetitions — not whether the exercise is done one arm or two — are the main drivers of growth [2]. In both cases, the evidence we’ve reviewed shows no meaningful difference in muscle growth between the two methods. The studies focus on beginners who are new to resistance training, and in that group, the body seems to respond similarly regardless of whether the load is distributed across one or both arms. This doesn’t mean one method is better — it just means that for someone starting out, either approach can lead to comparable results if the overall training volume is kept the same. We don’t have data on longer training periods, advanced lifters, or other muscle groups, so we can’t say whether this holds true beyond eight weeks or for people with more experience. But based on what we’ve reviewed so far, untrained women can choose either unilateral or bilateral curls without expecting one to outperform the other in terms of biceps growth. The key takeaway? Focus on lifting enough total weight over time — not on whether you use one arm or two.