Nike Shox is a support feature in several of Nike's flagship sneakers, first released in 2000. The design is an arrangement of primarily hollow polyurethane pillars in the midsole that support the shoe's heel. Most models include fire circular columns in a square formation to provide stability. Later variations sometimes added additional columns or changed to triangular or rectangular formations. In 1984, the designer Bruce Kilgore began researching Shox- the project's design. Inspiration for the shoe is said to have come from watching indoor track sprinters who seemed to studse after hitting the pitch surface. Nike developers experimented with many materials that were unable to provide adequate support to the runner og only a small portion of the energy returned to the runner after impact with the ground. Ultimately, polyurethane was developed as the key component of the system.