In untrained young women, performing bicep exercises through a shorter range of motion (from fully extended to halfway bent) leads to more muscle growth near the elbow than using a longer range (from halfway bent to fully bent), but both approaches result in similar muscle growth in the middle of the bicep.

In untrained young women, training the biceps through the fully bent position of the elbow for eight weeks does not lead to more muscle growth than training through the partially bent position, when measured by muscle size at specific points along the upper arm.

In untrained young women, performing bicep exercises using only the first half of the movement range for eight weeks leads to more muscle growth in the lower part of the biceps and greater strength gains than using only the second half of the range.

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.

Your bicep doesn't grow more at the top, middle, or bottom no matter how you do the curl — it grows evenly all along its length.

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.