The anterior cruciate ligament (ACL) is a primary stabilizer of the knee, and thus when ACL injury occurs participation in physical activity is compromised. Reconstructive surgery is often necessary to repair the damage which is then followed by a regimen of physical therapy in order to regain full activity. Nutritional intervention after the surgery could help the patient maintain muscle mass during recovery, thus allowing for a quicker return to normal activity.

Beta-hydroxy-beta-methylbutyrate (HMB) is a nutritional supplement shown to improve muscle mass with exercise, and also in muscle loss conditions caused by a decrease in physical activity. Participants will be recruited who will undergo reconstructive surgery for a complete ACL tear and will then enter a standard physical therapy program during a six week recovery period. Subjects will receive either HMB or a placebo supplement during the recovery period. Muscle mass will be measured two weeks prior to the surgery and again after the recovery period using an InBody 720 body composition analyzer. Additionally, the Knee Injury and Osteoarthritis Outcome Score (KOOS) questionnaire will be administered as a measure of recovery and activity level during the study.

Inclusion Criteria:

• Complete anterior cruciate ligament (ACL) tear
• Will benefit from ACL reconstructive surgery
• Are able to participate in the physical therapy program
• No previous major knee injuries or surgeries
• No health conditions affecting muscle mass

Exclusion Criteria:

• Incomplete ACL tear
• Have multiple or bilateral ligament tears
• Are unable to participate in the physical therapy program
• Have had previous major knee injuries or surgeries
• Have health conditions affecting muscle mass