The spikes on the balls help to increase blood circulation, warm the muscles and release toxins which make them particularly beneficial for use before and after exercise and for individuals who suffer from poor circulation. There are three different sizes of massage balls in the set. The 3.55" ball is perfect to use on the back, the 7.56" is designed for use on your arms and legs and the 7cm ball is ideal for use on your hands and feet. Features Spiky massage balls are perfect for an all-over body massage. Use the balls to apply pressure to the body to relieve tightness and discomforts and to encourage the muscles to relax. They are particularly beneficial for use before and after exercise.