Yakima Sport training sled model II 100331 Properties: Power Sled Sac Indoor/outdoor variable load sprint trainer Variable weight sleds allow you to strengthen your lower body muscles through resistance training similar to a metal sled. Thanks to the removable weights, the SpeedSac allows you to adjust the resistance when towing. You can also use the handles on the bags to perform a variety of upper and lower body exercises, such as lunges or front raises. Includes 3 heavy-duty weight bags that can be filled with up to 5kg of sand (15kg total). Will not harm grass or wood surfaces. Adjustable waist belt length to accommodate athletes of all sizes.