"Versatile high-density rubber platforms work to stretch and strengthen the Achilles tendon and calf muscles. Developing muscle resiliency in the area is vital to explosive leg power. Jump Soles will blast your lower legs like nothing else you've ever tried. After training with Jump Soles, you'll run faster, jump higher and change direction quicker. Simple Velcro strap on - available in four sizes. Also includes detailed training manual and video."