When you move your arm backward, it stretches your biceps because the muscle runs over your shoulder joint — and when you move your arm forward, the biceps gets shorter.
Evidence from Studies
Supporting (2)
Community contributions welcome
The study changes shoulder position during bicep curls, which affects how stretched the biceps muscle is—just like the claim says. When the arm is behind the body, the biceps get stretched; when in front, they shorten.
Biceps brachii regional shear modulus following elbow flexion exercises at different muscle lengths.
When the arm is stretched back (shoulder extension), the biceps gets longer and tighter, especially the part near the shoulder. This study found more tension in that area when the shoulder was extended, which supports the idea that the biceps lengthens in that position.
Contradicting (0)
Community contributions welcome
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.