Sklz SpeedSacOutrun The Competition! Is your lack of speed preventing you from becoming a gamebreaker If so, this training aid can help. Its use of variable weight strengthens your lower half, which enables you to explode from a set position. On the court, on the field. It doesn't matter. For once, you'll be ahead of the pack! SKLZ Speed Sac Sprint Trainer features: * Quickly improve your overall speed and explosiveness * Safely strengthen lower body muscle groups