When you curl with your arms behind you, your biceps stretch more and grow more than when you curl with your arms in front.
Scientific Claim
Curling exercises that position the shoulder in extension (lengthening the biceps) produce greater hypertrophy in the biceps brachii compared to exercises that position the shoulder in flexion (shortening the biceps).
Original Statement
“As for the biceps, we have five studies comparing curling with the shoulder extended to curling with the shoulder flexed. The biceps are placed at a longer length with the shoulder extended. Four of them made this comparison by comparing incline curls to preacher curls, while one of them compared cable incline curls to cable preacher curls. The findings are mixed, but once again, I'd argue that the stronger study designs demonstrate greater biceps hypertrophy from shoulder extended curls.”
Context Details
Domain
exercise
Population
human
Subject
biceps curling with shoulder extension
Action
produces
Target
greater hypertrophy in the biceps brachii compared to curling with shoulder flexion
Intervention Details
Evidence from Studies
Supporting (0)
Contradicting (2)
The study found that curling with your arm stretched out behind you (shoulder extended) didn’t make your biceps grow bigger than curling with your arm in front of you (shoulder flexed)—so the claim is wrong.
Placing Greater Torque at Shorter or Longer Muscle Lengths? Effects of Cable vs. Barbell Preacher Curl Training on Muscular Strength and Hypertrophy in Young Adults
The study compared two types of bicep curls—one that stretches the bicep and one that shortens it—and found both built muscle equally well, so stretching the bicep doesn’t make it grow bigger than shortening it.