Round head: Suitable for massaging larger muscle groups such as shoulders, waist, arms, hips, thighs, and calves. U-shaped head: Suitable for massaging the back, the sides of the spine and calves. Flat head: Suitable for relaxing all muscles. Illustrations of product, accessories, and user interface in the user manual are for reference purposes only. Actual product and functions may vary due to product enhancements.