Shoulders assist in stride length and speed. If the shoulders aren't trained for speed like the lower body then the lower body has to compensate for the upper-body's inadequacy. The Shoulder Surge device encourages the athlete to focus on upper body form and functional shoulder strength as the shoulders drive through the resistance provided by the sleeved elastics. 1 Universal Swivel Belt, 2-4' elastics, 2-biceps straps.