Build explosive leg drive, and speed with SpeedSac. This variable weight sled allows you to strengthen your lower body muscles by resistance training. With removable weights, the SpeedSac allows you to adjust the towing resistance. You can also use the handles on the bags to perform various upper and lower body exercises such as lunges or front raises. Note: Only use on grass, turf or wood surface. Use on any other surface may damage and/or shorten the lifespan of the product. Features: Includes 3 durable weight bags that can each be filled with up to 10 lbs of sand (30 lbs total). Adjustable leash length to accommodate athletes of any size.