The curling exercise, also called the bicep curl, is a weight training exercise used to improve the size and strength of the bicep muscles, which are located on the upper arms. The results obtained from this exercise depend on the techniques used and the number of repetitions performed.
Performing curls can increase the size of the biceps when lifting weight sufficient enough to cause small tears, or "micro-tears," in the muscles. When the body repairs micro-tears, the healed tissue may be larger and better adapted to performing the exercise that caused the tears. Therefore, the gains from weight lifting occur during the days of recovery, and not in the gym when the exercises are being performed.