According to the American Academy of Orthopedic Surgeons, an estimated 70 percent of ACL injuries occur for reasons not caused by impact injuries, with injury incidence increased in the female population. An ACL injury almost always means surgery, with a lot of down time--and recovery--needed to heal the entirety of the injury. If you have recently injured your ACL, your physical therapist may recommend the following exercises to improve healing:Passive Knee ExtensionHow to do: Sitting in a chair, place your heel on another chair in front of you. Allow your leg to relax while keeping the knee straight. Keep this position for one to two minutes.Prone Knee FlexionHow to do: Lying on your stomach, keep your legs straight against the ground. Now slowly bend your knee, bringing the heel of your foot close to your buttocks. Hold this for five seconds before returning to the starting position. Repeat 10 times.Heel RaiseHow to do: Standing up, place your hair on a chair or solid surface. This will help you balance. Now raise both feet up so you're only on your toes and hold this position for five seconds. Slowly lower back onto your heels. Repeat this 10 times.One Leg StandHow to do: This one is very simple. Standing up, simply raise the calf of your uninjured leg against your buttocks. Now try to balance on your injured leg for at least 10 seconds. Do this as much as recommended by your physical therapist.Half SquatHow to do: Use a table or chair as support if necessary. Keeping your feet shoulder's width apart, slowly bend down into a squatting stance by leading out with your buttocks. Eventually lower yourself until your upper legs are parallel to the ground. Hold this for 10 seconds before returning to the starting position. Continue for 10 repetitions.Remember, follow the instructions given by your physical therapist first--these instructions are personally tailored to improve your recovery time.