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.

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Evidence from Studies

Supporting (1)

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Small muscle mass exercise enhances muscular adaptations? Effects of unilateral and bilateral biceps curl on maximum strength and muscle size changes.

Randomized Controlled Trial

Human

2025 Dec 8

Both ways of doing bicep curls—using both arms at once or one arm at a time—led to the same amount of muscle growth in the arms after 8 weeks, so neither way is better for building bigger biceps.

Contradicting (0)

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No contradicting evidence found

Source Study

Small muscle mass exercise enhances muscular adaptations? Effects of unilateral and bilateral biceps curl on maximum strength and muscle size changes.

Score: 61

DOI: 10.1007/s00421-025-06033-4

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