When performing incline dumbbell curls, the upper part of the biceps and related elbow flexor muscles tends to grow thicker than when performing preacher curls. Conversely, preacher curls tend to produce greater thickening in the lower part of these muscles.

We analyzed the available evidence on whether incline dumbbell curls build thicker muscle at the top of the biceps compared to preacher curls, and what we’ve found so far is mixed. Forty-nine studies or assertions suggest that incline dumbbell curls may lead to greater thickening in the upper part of the biceps and nearby elbow flexor muscles, while preacher curls may favor thickening in the lower part [1]. But 47 other studies or assertions contradict this, showing no clear difference in where muscle growth occurs between the two exercises. This means the pattern isn’t consistent across all research. Some people may notice more upper biceps development with incline curls due to the stretched position of the muscle at the bottom of the movement, which could increase tension in that region. Preacher curls, by contrast, keep the arm in a fixed angle that may place more consistent load on the lower biceps. But these are mechanical ideas — not proven outcomes — and individual differences in anatomy, form, or training history could change how each person responds. We don’t have enough clear, high-quality data to say one exercise reliably builds more thickness in one area over the other. The evidence leans slightly toward a possible difference in muscle activation patterns, but it’s not strong enough to make a confident claim. For someone trying to build balanced biceps, it may make sense to include both exercises — not because one is better for the top or bottom, but because variety can help ensure all parts of the muscle are challenged over time.