The hammer curl is a variation of the traditional bicep curl, where the palms face each other (neutral grip). This exercise places greater emphasis on the brachialis muscle, which lies underneath the biceps, and the brachioradialis, a muscle in the forearms. This exercise is ideal for increasing arm thickness and developing the often-undertrained brachialis, which helps push the biceps up for a fuller appearance. The neutral grip also reduces stress on the wrists and elbows, making it a joint-friendly movement. Perform with controlled motion to avoid using momentum and fully engage the muscles.