SKLZ Speedsac- Adjustable Weight Sled Trainer for Sprinters (10-30 lbs). BUILD STRENGTH AND SPEED. Develop explosive power with the SKLZ Speedsac. Improve 40-yard dash times, overall speed, and lower body muscle strength with this adjustable weight sled trainer for serious athletes. IMPROVE ENDURANCE. Get more powerful leg drive with the SKLZ Speedsac. Use it for sprinting, backpedaling, and shuffling to increase mobility and agility in any direction. This training sled will give you the power and speed youre looking for. MULTI-SURFACE FUNCTIONALITY. Use on grass, turf, or wood surfaces for a multi-surface option. Take your workout indoor or outdoor without the limitations of a gym. The durable shell bag, and secure weight bags stay in place as you work hard. VARIABLE WEIGHT RESISTANCE. With three, 10 lb. removable weight bags, you can alter your resistance training based on your athletic needs. Adjust the leash length to accommodate athletes of any size. INVEST IN YOUR GOALS. Investing in sports equipment means investing in your training and athletic goals. Find the power in your stride, sprint, and distance as you use the SKLZ Speedsac Variable-Weight Sprint Trainer to push yourself and meet your goals