The study is a prospective randomized control trial consisting of subjects requiring ACL reconstruction with BTB autograft. Subjects were randomly divided into two groups following their inclusion in the study. One group underwent the normal ACL rehab protocol as determined by the participating surgeons. The study group underwent normal ACL rehab modified by use of a tourniquet for blood flow restriction during selected exercises.

On the day of the procedure, the surgeon will measure the subject's thigh circumference 1/3 distance from the superior pole of the patella to the inguinal crease. The subject will then undergo the normal BTB autograft ACL reconstruction procedure. A subject will be excluded from the study if a meniscal repair is performed. At the subject's two week post-operative clinic visit, the physician will measure thigh circumference at 1/3 distance from the superior pole of the patella to the inguinal crease. Study group subjects will begin physical therapy instructed BFR exercises at two weeks post operatively. Study group subjects will be taken through normal ACL rehab protocol as well as BFR exercises. Control group subjects will do the same exercises and formal physical therapy rehab protocol as the study group without BFR.

The BFR exercises will consist of: bilateral leg press week 3-10, eccentric leg press weeks 4-10, hamstring curl week 4-6, eccentric hamstring curl weeks 7-10, straight leg press weeks 6-10. The pressure used will be elevated to occluded blood flow by 80% (80% occlusion pressure) which will be determined for each individual subject. Subjects will do exercises at 20% of 1RM in 4 sets of 30-15-15-15 repetitions separated by 30 seconds of rest. Repetition maximum (1RM) will be determined by the contralateral leg, using the greatest amount of weight with full range of motion and proper form. This will be done over three separate tries, separated by one minute breaks. Resistance loads will be adjusted every 2 weeks as strength improves. During the exercise protocol, if patients are unable to complete the prescribed amount of repetitions, rest periods between sets will be increased as needed. The control group will do these exercises without BFR. Both study and control groups will also do the surgeons' standard post-ACL reconstruction physical therapy protocol.

Cuff pressures will be determined using the Loenneke et al outline, based off of thigh circumference and estimated cuff pressure for 50% artery occlusion [19].

Body composition (DEXA), bone density (DEXA), IKDC and Tegner Lysholm scores will be recorded at first rehabilitation visit, two weeks, eight weeks and 12 weeks following the initiation of rehab (1 wk following surgery). Y- balance, single leg squat distance, and single leg step down will be measured at 8 weeks and 12 weeks of rehab. Return to play will be recorded as the number of months after the day of operation until subject returns to sport.

Inclusion Criteria:

• Ages 18-35
• Received ACL surgery with a patellar tendon autograft

Exclusion Criteria:

• Concomitant meniscal tear or additional ligamentous injury to the knee
• Obesity (BMI>30)
• Diabetes
• Cardiovascular, renal, liver or pulmonary disease
• Active infections
• Cancer (current or treated within the past 2 years) or coagulation disorder
• Rapid weight change within the past year
• Physically unable to participate in the intervention
• Are not currently taking, or recently (w/in 1month of participation) taken prescribed or over the counter ergogenic aids or compounds known to be banned by the NCAA. The NCAA banned substances list can be viewed from: http://www.ncaa.org/health-and-safety/policy/2014-15-ncaa-banned-drugs
• Unable to complete a minimum of 85% of the assigned rehabilitation sessions.

12 weeks after surgery