When lowering a barbell during a bicep curl, the biceps muscle activates more when the arms are hanging straight down than when the shoulders are bent forward, and this difference is larger with an...

We analyzed the available evidence on shoulder position and biceps activation during the lowering phase of a bicep curl, and what we’ve found so far suggests that shoulder position may influence how much the biceps are engaged. Specifically, when the arms hang straight down at the start of the lowering phase, the biceps appear to activate more than when the shoulders are bent forward [1]. This difference in activation was noted to be more pronounced when using an EZ bar compared to a straight bar [1]. We did not find any studies or assertions that contradicted this observation. The evidence we’ve reviewed leans toward the idea that keeping the shoulders in a neutral, relaxed position — rather than hunched forward — may lead to greater biceps involvement during the controlled descent of the curl. However, we only have one assertion to work with, and it does not include details on participant size, training level, or how activation was measured. Because of this, we cannot say whether this effect is large, consistent across all people, or meaningful for muscle growth. For now, if you’re looking to potentially maximize biceps engagement during the lowering part of a curl, keeping your shoulders relaxed and arms hanging straight down — especially with an EZ bar — might be worth trying. But more research is needed to understand how this plays out in real-world training.