Mobility is indeed a crucial aspect of ACL tear rehab, especially when it comes to regaining full range of motion in the knee joint. Flexion and extension are the two primary movements that are important to focus on during the early stages of rehabilitation. In the initial phases of rehab, the focus is on reducing swelling and pain, and regaining the ability to move the knee joint through its full range of motion. This involves working on flexion (bending) and extension (straightening) exercises to prevent the knee from becoming stiff. Once mobility is regained, the focus shifts towards strengthening exercises to rebuild the muscles around the knee joint. Strengthening exercises help to improve stability and balance, which are important for preventing future injuries.