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Claim
Strong Support
quantitative
Analysis v3

If new gym guys do a specific arm curl workout for 10 weeks — going until their muscles are totally tired — their biceps get about 7% to 9% thicker, no matter how their shoulders are positioned, as...

60
Pro
0
Against

Mechanism

Synthesis from 1 study

How it works

When you lift until you can't do another rep, your biceps get pulled hard enough to trigger them to grow thicker. Doing this the same way every time—with full motion and steady resistance—makes the whole muscle grow evenly, no matter how your shoulder is positioned.

Most probable mechanism

In Simple Terms

When the biceps are worked hard until they can't do another rep, the muscle fibers stretch and pull against resistance, which sends signals inside the cells to build more muscle proteins. Over time, this makes the muscle fibers thicker, and since the exercise is done the same way every time with full movement and consistent resistance, the thickening happens evenly along the whole muscle.

Causal chain
1

Repeated concentric and eccentric contractions under load generate sustained mechanical tension across muscle fibers.

Supported by evidence
which leads to
2

Mechanical tension activates intracellular signaling pathways, including mTORC1, that increase the rate of muscle protein synthesis.

Indirect evidence only
which leads to
3

Protein synthesis exceeds protein breakdown over the 10-week training period, resulting in net accretion of contractile proteins within muscle fibers.

Indirect evidence only
which leads to
4

The uniformity of resistance profile and full range of motion ensures consistent mechanical loading along the entire length of the elbow flexors, leading to proportional thickening at both proximal and distal regions.

Supported by evidence

Evidence from Studies

Supporting (1)

60

Community contributions welcome

60

The effects of shoulder extension angle on elbow flexor hypertrophy in the cable curl exercise

Randomized Controlled Trial
Human
2026

Contradicting (0)

0

Community contributions welcome

No contradicting evidence found

Gold Standard Evidence Needed

According to GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this specific claim, ordered from strongest to weakest evidence.

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Source Study

The effects of shoulder extension angle on elbow flexor hypertrophy in the cable curl exercise

Score: 60
DOI: 10.3389/fphys.2026.1750722

Similar Assertions

If new guys do a specific arm curl workout for 10 weeks — going until their muscles are totally tired — their arm muscles get about 7% to 9% thicker, no matter how their shoulders are positioned, as long as the movement and resistance stay the same.

60
0
100%

In men who are new to strength training, doing cable curls until muscle fatigue for 10 weeks leads to about the same increase in bicep muscle size whether the shoulder is kept straight back or pulled slightly backward, as long as the resistance and effort level are kept the same.

60
0
89%

If you're new to lifting, changing your arm position during cable curls doesn't make one part of your biceps grow more than another — both positions give you the same kind of muscle growth over 10 weeks if everything else is kept equal.

60
0
87%

In untrained men performing cable curls with the same resistance, movement range, and effort, changing the shoulder angle between neutral and fully extended positions leads to similar increases in elbow muscle thickness after 10 weeks of training.

60
0
87%

If you're new to lifting and do cable curls the same way each time, it doesn't really matter whether your arms are stretched far back or in a neutral position — your biceps will grow about the same amount after 10 weeks.

60
0
86%