If you do cable curls the same way every time except for where your shoulders are, it doesn’t really matter for building arm muscle—even if you can lift heavier when your arms are stretched out.
Mechanism
Synthesis from 1 study
Your muscles grow based on how long they’re working hard and how much burning feeling they get, not just how heavy the weight is. Even if you can lift more with your arm stretched out, if the total work and burn feel the same as when your arm is relaxed, your biceps grow just as much.
Most probable mechanism
When you lift weights, your muscles grow not because of how heavy the weight is, but because of how long they’re under tension and how much burning sensation they feel from built-up chemicals. Even if you can lift heavier with your arm stretched out, if the total time your biceps are working and the chemical buildup inside them are the same as when you lift lighter with your arm relaxed, your muscles grow just as much.
Muscle fibers experience similar total time under tension during contractions regardless of shoulder position when range of motion and effort are matched.
Metabolic byproducts such as lactate and hydrogen ions accumulate to comparable levels in elbow flexors due to matched effort and movement patterns, activating cellular signaling pathways linked to protein synthesis.
Mechanical tension thresholds required to trigger hypertrophy are reached and sustained similarly across shoulder positions when effort and volume are equated, despite differences in peak load.
Evidence from Studies
Supporting (1)
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The effects of shoulder extension angle on elbow flexor hypertrophy in the cable curl exercise
Contradicting (0)
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