After an anterior cruciate ligament (ACL) reconstruction, some people have unusual muscle reactions around the knee, called arthrogenic muscle responses (AMR). These muscle responses might help protect the knee at first, but if they last too long, they could harm the knee and might even lead to arthritis later. This study will see if adding mental exercises to physical therapy helps control these muscle responses better than physical therapy alone. The study will involve checking the muscle responses 5 months after surgery. If AMR is found, participants will be randomly placed in one of two groups for treatment for six weeks. Researchers will check the knee again at 7 and 9 months after surgery to see how the treatments work.

• Study length: 9 months, with two 6-week treatment sessions.
• Requires visits for therapy twice a week for six weeks.
• Participants must be 18-40 years old and have had ACL surgery.