This SKLZ Speed Sac variable-weight resistance sled trainer helps sprinters, football players, and other athletes strengthen and develop lower body muscles to improve speed and explosiveness. The three removable weight bags can each be filled with up to 10 pounds of sand for a total of up to 30 pounds of resistance (sand is not included). A 360-degree belt ring allows for multi-directional training to help increase mobility and agility in every direction. The SKLZ Speed Sac is built with durable nylon materials for long lasting performance on grass, turf, or wood surfaces. Velcro-secured straps hold weight bags firmly in place no matter how hard the workout, and the fully-adjustable leash accommodates athletes of any size. Includes Speed Sac shell, 3 sand bags (sand not included), adjustable leash and belt with 360-degree ring. Limited 1-year manufacturer's .