Quadriceps muscle weakness is a common consequence following anterior cruciate ligament (ACL) injury and reconstruction. Maximizing quadriceps strength following ACL injury is significant as diminished quadriceps strength has been linked to the osteoarthritis that affects over 50% of surgically reconstructed limbs. Given that knee joint health following ACL injury is predicated on restoring quadriceps strength, identifying treatment approaches capable of improving strength is paramount. Blood flow restriction training (BFRT) is a method where oxygen to the muscle is intentionally reduced during exercise/rehabilitation and may lead to more timely and substantial strength gains. In the proposed project, we will examine the efficacy of BFRT in patients who have undergone ACL reconstruction and suffer from substantial quadriceps weakness.

Quadriceps muscle weakness is a common consequence following anterior cruciate ligament (ACL) injury and reconstruction. Maximizing quadriceps strength following ACL injury is significant as diminished quadriceps strength has been linked to the osteoarthritis that affects over 50% of surgically reconstructed limbs. Given that knee joint health following ACL injury is predicated on restoring quadriceps strength, identifying treatment approaches capable of improving strength is paramount. Blood flow restriction training (BFRT) is a method whereby oxygen to the muscle is intentionally reduced during exercise/rehabilitation and may lead to more timely and substantial strength gains. In the proposed project, we will examine the efficacy of BFRT in patients who have undergone ACL reconstruction and suffer from quadriceps weakness. This project will have a randomized clinical trial design. Sixty patients that have torn their ACL and plan to undergo surgical reconstruction will be randomized into one of four groups: 1) eccentric exercise; 2) concentric exercise; 3) eccentric exercise with blood flow restriction; or 4) concentric exercise with blood flow restriction. All patients regardless of randomization assignment will also receive standard of care ACL rehabilitation. Approximately 6 weeks after ACL reconstruction surgery, patients will begin to receive the study interventions which will last for 8 weeks. The concentric exercise will be a leg press exercise done on a conventional leg press machine, while the eccentric exercise will be a leg press exercise done on a device designed to elicit eccentric muscle contractions. Patients will train at 70% of their 1 repetition maximum and will complete 4 sets of 10 contractions at each session (2 sessions/week). For patients randomized to the BFRT groups they will complete the leg press exercise while blood flow the the quadriceps muscle is restricted with a BFRT device (Delfi Personalized Tourniquet System for Blood Flow Restriction). We will quantify our dependent variables prior to surgical reconstruction, 6 weeks post-operatively (before study intervention starts), 14 weeks post-operatively (immediately after study intervention ends), and time of physician discharge from rehabilitation (e.g. time medical clearance for return to activity). The primary outcome is isokinetic quadriceps strength. We hypothesize that patients who complete eccentric exercise along with blood flow restriction training will realize the greatest gains in muscle strength.

The DELFI PTS Personalized Tourniquet system is exempt from premarket notification and is therefore not subject to 510(k)

Inclusion Criteria:

1. suffered an acute, complete ACL rupture as confirmed by MRI
2. scheduled to undergo ACL reconstruction
3. scheduled to undergo ACL reconstruction with a surgeon affiliated with MedSport (University of Michigan Orthopaedic Clinic)
4. willing to undergo rehabilitation through MedSport (University of Michigan Orthopaedic Clinic) 5)) Willingness to participate in testing and follow-up as outlined in the protocol

6) English-speaking

Exclusion Criteria:

1. inability to provide written informed consent (or assent)
2. female subjects who are pregnant or are planning to become pregnant during the study timeframe
3. previous ACL injury
4. previous surgery to either knee
5. bony fracture accompanying ACL injury
6. chronic ACL injuries (for our study, this is defined as patient reporting to a physician greater than 2 weeks after initial injury)
7. patients who experienced a knee dislocation
8. History of blood clots
9. Previous deep vein thrombosis
10. Use of estrogen or progestin contraceptive
11. History of cerebrovascular disease
12. History of peripheral vascular disease
13. History of Sickle Cell Anemia
14. History of chronic muscular disorder (e.g. fibromyalgia)
15. History of severe hypertension