Sculls (hand movements used to propel the body) are the most essential part to synchronized swimming. Commonly used sculls include support scull, stationary scull, propeller scull, alligator scull, torpedo scull, split-arm scull, barrel scull, and paddle scull. The support scull is used most often to support the body while a swimmer is performing upside down. Support scull is performed by holding the upper arms against the sides of the body and the lower arms at 90-degree angles to the body, with hands facing the bottom of the pool. The lower arms are then moved back and forth while maintaining the right angle. The resulting pressure against the hands allows the swimmer to hold their legs above water while swimming. Other sculls used in training include propeller and reverse propeller.