Click here for awesome long jumping photos. There are two phases of muscle contraction during the running and jumping motion.
Muscles go through a stretch phase and then a contraction phase.
Plyometrics are designed to shorten the cycle time between the two phases. Therefore, plyometrics are great exercises for runners and jumpers. Click here for more information on plyometrics. After takeoff, the hips remain forward, and the arms are used for balance. The related links mentioned above.