Strength training¿especially for the hamstrings and quadriceps¿is crucial for preventing an ACL tear. Develop a leg program at the gym that includes leg presses, hamstring curls and abductor and adductor work. (Talk to a trainer for more specifics.) In addition to weights, there are several other at-home devices you can use. The Skier's Edge is among the best. This ski conditioning machine builds strong knees and lateral power by mimicking the ski motion¿just hop on and push from left to right. It's also a tremendous calorie burner, zapping up to 800 calories per hour. Ten national ski teams, including the U.S. squad, train on the Skier's Edge. But it's not just for racers¿it will push anyone's quads, hamstrings and calves to the max. Because it comes with all the necessary tools for assembly, the Skier's Edge is easy to put together, but it's heavy to move once you have it in place. Price: $695. Call Skier's Edge, (800) 225-9669.