Jumpsoles are the world's most popular frontal training platforms which attach to your own shoes. By training with Jumpsoles you will build up important fast twitch muscle fibers in the lower leg. Jumpsoles will increase vertical jump by 5 to 10 inches, and decrease time in the 40 yd dash by .2 seconds! Comes complete with training manual and video. The Jumpsoles are now upgradeable with the all new Proprioceptor System! The version 4.0 were specially designed to use this device which develops balance and agility while preventing injury. Available in sizes S-XL.