While there are a number studies that have reported on the use of BFR in the adult population, there is limited information about the use of BFR in the adolescent population. This study aims to evaluate the use of BFR training in conjunction with traditional ACL (anterior cruciate ligament) reconstruction rehabilitation in adolescents.

The purpose of this study is to evaluate the addition of BFR-based exercise to traditional methods of physical therapy. Does the use of BFR-based exercise improve strength, hypertrophy, functional and patient reported outcomes after ACL Reconstruction in the adolescent population?

The planned pilot study is a prospective case control study utilizing retrospective controls. The investigators will compare the use of exercises augmented with BFR with quantitative measurements of strength and patient reported outcomes. A total of 20 youth and adolescent patients undergoing a surgical procedure for ACL reconstruction at Connecticut Children's Elite Sports Medicine and completing physical therapy at Connecticut Children's Sports Physical Therapy will be recruited for this study. A review of data from 20 previous patients, matched for age, sex, BMI and surgical procedure that completed physical therapy at Connecticut Children's Sports Physical Therapy will be used as a comparison.

As part of this pilot study, the investigators will additionally collect prospective controls. This population will be patients not participating in physical therapy at Connecticut Children's, but underwent ACL reconstruction by Elite Sports Medicine. The investigators are unsure of the ability for us to collect prospective controls in a timely manner, hence the investigators will use the above described retrospective cohort as controls if the prospective controls prove difficult to recruit.

Identification and Recruitment:

All potential patients undergoing ACL reconstruction at Elite Sports Medicine will be approached for participation for this study. Eligible patients will be identified at their initial pre-operative appointment with the Sports Medicine Physician, Athletic Trainer, and Sports Physical Therapy Physical Therapist. Subject selection will be completed by those patients meeting the above outlined inclusion and exclusion criteria. At this time, the study purpose and protocol will be explained and a brief summary of the study will be provided.

Consent: Consent will take place at the pre-operative visit. The patient/parent will be given a detailed description of the purpose and methodology for this study. The participants will have the opportunity to read the consent forms and ask any questions they may have about the research. If the patients agree to participate, they will be asked to sign the consent form and a copy will be provided.

Retention: Eligible patients will be required to be seen for a minimum of 90% of patient visits to be included in this study.

In addition to the standard ACL protocol, patients in this study will utilize the Owen Recovery Science exercise protocol for BFR [18]. The following guidelines will be followed concerning exercise progression, occlusion pressure and difficulties with volume achievement. To determine the appropriate resistance for each exercise, the patient's 1 repetition maximum (1RM) will be attained using a repetition test [19]. This test will use a previously validated algorithm to determine the 1RM based on the weight used to perform a 7-10 repetition test [20]. Patient will perform the exercise with a weight they can comfortably lift for several repetitions. Based on the weight or resistance used, and the patient's perceived exertion a 1RM will be estimated using the modified OMNI-RES (OMNI perceived exertion scale for resistance). The starting load for each exercise will be 20-30% of their 1RM , or bodyweight resistance will be used when loading is not feasible.

Proposed Protocol Phase 1- Weeks 1 to 2

• Quad Set: 10 second on, 10 second rest at 100% occlusion x10'

  o progress to isometrics at the edge of the table 60 degrees as clinically appropriate

• Side Lying Hip Abduction, 30/15/15/15, at 80% occlusion

• Hip Extension from prone 30/15/15/15, at 80% occlusion

• Re-check load at the start of each Phase, to determine 1 RM (7-10 RM (repetition maximum) test on leg press)

• Total BFR time approximately 24 minutes per session, with 2 sessions per week

Phase 2- Weeks 3 to 4

• Replace Quad Set with Long Arc Quad (90-30deg), 30/15/15/15 at 80% occlusion
• Replace Hip Extension with Leg Press (shuttle), 30/15/15/15 at 80% occlusion
• Hip Abduction, 30/15/15/15 at 80% occlusion
• Total BFR time approximately 24 minutes per session with 2 sessions per week

Phase 3- Weeks 5 to 6

• Long Arc Quad (90-30deg), 30/15/15/15 at 80% occlusion
• Leg Press (shuttle), 30/15/15/15 at 80% occlusion
• Replace Hip Abduction with Bilateral Hip Bridge, 30/15/15/15 at 80% occlusion
• Total BFR time approximately 24 minutes per session, with 2 sessions per week

Phase 4- Weeks 7 to 8

• Leg Press (shuttle), 30/15/15/15 at 80% occlusion
• Replace Long Arc Quad with Step Up 30/15/15/15 at 80% occlusion
• Bilateral Hip Bridge, 30/15/15/15 at 80% occlusion
• Total BFR time approximately 24 minutes per session, with 2 sessions per week

Phase 5- Weeks 9 to 12

• Replace Bilateral Hip Bridge with Medial Step Down, 30/15/15/15 at 80% occlusion
• Replace Step up with Split Squat, 30/15/15/15 at 80% occlusion
• Leg Press (shuttle), 30/15/15/15 at 80% occlusion
• Total BFR time approximately 24 minutes per session, with 2 sessions per week

Phase 6- Weeks 11 to 12

• Progressively load exercises from phase 5
• Total BFR time approximately 24 minutes per session, with 2 sessions per week

Inclusion Criteria:

• Patients between the age of 12 and 18 years at the time of surgery.
• Post-primary ACL reconstruction
• Orthopaedic surgical intervention (including all additional procedures at the knee) completed by one of the Elite Sports Medicine physicians.
• Patient completed postoperative rehabilitation following standard protocols
• No contraindications to performing BFR, as outlined in the Owens Recovery[18] Science 2018 Personal Blood Flow Restriction manual.

Exclusion Criteria:

• Patients older than 18 and younger than 12 at the time of surgery
• Any additional diagnoses or deformity not related to knee injury that could affect knee strength
• Additional lower extremity injury at time of knee injury (e.g., ankle injury) requiring treatment
• Previous surgical intervention on the knee (ipsilateral and contralateral)
• Patients with weight bearing restrictions for greater than two weeks after surgery due to concomitant pathology such as meniscal root/radial repair, chondral pathology, or multi-ligament pathology. . Generic exclusion: "Subjects not meeting all inclusion criteria."

Adverse events were collected during the study time period when patients were completing BFR training during their physical therapy session for 12 weeks.

monitoring for the following side effects: subcutaneous hemorrhage (SubQ), deep vein thrombosis (DVT), fainting, dizziness, lower extremity paresthesia, and itching

Covid-19 pandemic Lost to follow up, surgical exclusion led to small number of controls.