Getting your blood circulating should always be your first step when working out with a weak ACL in mind. Light jogging, bike machines, and treadmill workouts are a great place to start. Camp also suggests warming up with dynamic exercises that emphasize balance, agility, and mobility, with a focus on your lower body and legs. Karaokes, in and outs, lateral drills, and incremental sprint drills can all help improve your overall lower-body strength and flexibility. "Light plyometric activity is another good way to start warming up your knees," he adds.