In untrained young women, doing biceps curls with both arms at the same time or one arm at a time leads to the same amount of muscle growth in the upper arm after 8 weeks, suggesting that how much...
Mechanism
Synthesis from 1 study
Your biceps grow because each tiny part of the muscle gets pulled hard enough during exercise — not because you're using one arm or two. If the pull on each part is the same, the muscle grows the same, no matter how you hold the weights.
Most probable mechanism
When you lift weights with one arm or both arms at the same time, each individual muscle fiber in your biceps still feels about the same amount of pull and stretch, as long as you're doing the same total amount of work. This consistent pull tells the muscle to grow, no matter if you're using one or two arms.
Total mechanical load is distributed such that muscle fiber-level tension is equivalent between bilateral and unilateral conditions when total work is matched
Muscle fibers experience similar levels of strain and force production per unit of muscle mass during each repetition
Sustained mechanical tension triggers intracellular signaling pathways (e.g., mTORC1) that promote protein synthesis at comparable rates in both conditions
Net protein balance becomes similarly positive over time, leading to equivalent increases in muscle fiber cross-sectional area
Evidence from Studies
Supporting (1)
Community contributions welcome
Small muscle mass exercise enhances muscular adaptations? Effects of unilateral and bilateral biceps curl on maximum strength and muscle size changes.
Contradicting (0)
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Gold Standard Evidence Needed
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