When people perform dumbbell curls, the part of the biceps closer to the elbow grows more than the part closer to the shoulder, suggesting that how force is distributed through the muscle depends on the exercise being done.

After 8 weeks of weight training, the upper part of the biceps grows more with both dumbbell curls and rows, while the lower part grows more with curls than with rows, indicating that different parts of the muscle respond differently to different exercises.

After 8 weeks of training, dumbbell curls lead to a 11% increase in muscle size near the elbow compared to dumbbell rows, which result in only a 1% change, suggesting that exercises involving a single joint may produce greater muscle growth in the distal part of the muscle.

In untrained young women, resistance training that focuses on the beginning part of the movement causes more muscle growth in the lower part of the biceps compared to training that focuses on the end part of the movement.

When people do light weight training with blood flow restriction on their biceps, the muscle grows evenly no matter if they do the exercise with their arm bent a lot or a little — growth looks the same along the whole muscle.

Doing bicep curls only halfway up (keeping the arm stretched) might make the lower part of your bicep grow a tiny bit more than doing full curls, but the difference is very small.