SPRI Triple Zone Massage Roller Roll away tension in multi-head lower body muscles (calf, hamstrings, quads) and upper body muscles close to the spine EVA rounded multi-ball design allows you to place the roller pressure in just the right location without unwanted pressure to untargeted muscles and bony areas Use two roller balls for single leg and smaller upper body areas Use three roller balls for dual-leg rolling and larger upper-body muscles Balls do not detach and are all the same density