When performing biceps curls with a weight that allows 8 repetitions, bending the arms during the upward motion increases electrical activity in the biceps muscle by about 18% to 20% compared to...

We analyzed the available evidence on arm position during biceps curls and found that bending the arms during the upward motion appears to increase electrical activity in the biceps muscle compared to keeping the arms straight. This was observed in measurements taken from trained bodybuilders using a weight that allowed about 8 repetitions, with activity rising by approximately 18% to 20% [1]. The evidence we’ve reviewed so far consistently points to this pattern — all 37 assertions support the idea that bending the arms during the curl leads to higher muscle activation. There are no studies or claims in our analysis that contradict this. The measurements reflect electrical signals from the muscle, which suggest the biceps are working harder when the elbow bends through its full range during the lift. This doesn’t mean one method is better for building muscle or strength — we don’t measure outcomes like growth or performance — but it does suggest that how you move your arm during the curl changes how much the biceps are firing. Keeping the arms straight, as described in the evidence, may reduce the muscle’s effort during the upward phase. What this means for someone lifting weights: if your goal is to feel your biceps working harder during each rep, focusing on a full bend at the top of the curl — rather than locking or stiffening the arms — may help increase that sensation. It’s a small detail, but one that could make a difference in how engaged you feel during the exercise. Our current analysis is based on one type of participant and one specific load. More research could explore how this applies to different people or training goals.