Lengthen and Strengthen In a normal standing position with conventional athletic shoes roughly 2/3rds of the body’s weight is supported or rests on the heels with little effort from the calf muscles. Training in the Katapult™ shoe eliminates the heel and forces the calf muscles to support the full body load. This overload works the calves and Achilles tendons with a force equal to several times the body's weight upon impact. Used correctly, the Katapult training shoe stretches and overloads these muscles, which in time will lengthen and strengthen. The Katapult™ Training Shoes will increase vertical jump five to ten inches, lower speed in the 40-yard dash by two tenths of a second, and improve lower leg strength and flexibility. Many well-known athletes use frontal platform shoes for training, to give them an extra edge, but the shoes can help even amateur athletes excel in any sport - basketball, football, soccer, track, volleyball, body building, baseball and more. Included with a Pair of Katapult™ Shoes The Katapult™ plyometric training shoe comes with a 52-week in-season off-season training methodology and DVD (patent pending), a laminated card to take to your workout and a stretch strap that will allow you to pre and post stretch.