Build explosive leg drive and speed right of the blocks with the SKLZ(R) SpeedSac. This variable weight sled allows you to strengthen your lower body muscles by resistance training similar to metal sleds. 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. Product Features Improve 40-yard dash times, overall speed and explosiveness Strengthen lower-body muscle groups Adjust weight options for variable weight resistance Adjustable leash length to accommodate athletes of any size Additional Details Includes 3 durable weight bags that can each be filled with up to 10 lbs of sand (30 lbs total)