Benefits of Blood Flow Restriction Training following ACL Surgery
What is Blood Flow Restriction (BFR)?
Blood flow restriction (BFR) is a training method that utilizes a tourniquet system to partially restrict arterial and venous blood flow to/ from working muscles. BFR training allows individuals to exercise with lower intensity, but still have the benefits of high-intensity training. A band or cuff is placed around the proximal limb to reduce, but not fully occlude, blood flow to the distal muscles. It is recommended for the lower limb that 80% of blood flow is restricted. We prefer pneumatic BFR cuffs that are inflated with an automated pump for specific and accurate limb occlusion pressure. Blood flow restriction training is safe and effective with over 20 years of research supporting its use in the rehabilitation field.
Muscles adapt through neural, mechanical, and metabolic mechanisms. The most significant mechanical factors contributing to muscle adaptation is volume and load. Important metabolites contributing to anabolic muscle adaptation include testosterone, growth hormone, and IGF-1. Testosterone stimulates protein synthesis and inhibits protein degradation.1 Growth hormone leads to increased IGF-1 concentrations. IGF-1 also has anabolic properties activating satellite cells leading to increased muscle fiber volume. Testosterone increases with high load resistance training while growth hormone is stimulated by low to moderate intensity and high volume resistance training.2
How does BFR work?
It is believed that blood flow restriction training works by the indirect effect of metabolite accumulation and the hypoxic environment created by training with limited arterial blood flow. It allows the working muscle to train under conditions of both high load and high volume.
The hypoxic environment created from restricted blood flow accelerates muscular fatigue and promotes recruitment of more high threshold motor units. These fast twitch muscle fibers are normally only recruited when training at higher intensity. The lower pH of the hypoxic environment also stimulates hypertrophic mechanisms.
Why is BFR beneficial following knee joint surgery?
Significant weakness and atrophy of the quadriceps muscle often occurs following knee joint surgery. Studies show knee extensor peak torque can decrease by 80 to 90% one to three days after knee joint surgery. This immediate decrease in muscle strength and size is due to a process called arthrogenic muscle inhibition (AMI).3 AMI following surgery is caused by changes in articular sensory receptors due to factors such as joint effusion, inflammation, joint laxity, and damage to afferent nerves.4
Arthrogenic muscle inhibition and disuse due to inactivity both lead to protein degradation. MRI quantitation in one study showed that 7 days of bed rest alone resulted in a 3% decrease in thigh muscle volume.5
Quadriceps weakness and atrophy are inevitable following surgery; however, blood flow restriction training has been shown to stimulate multiple pathways that help attenuate muscle atrophy, increase muscle protein synthesis, and increase strength. In the early phases of healing, heavy loads are not appropriate because it may overload and damage the healing tissue.
Blood flow restriction training allows for the benefits of high load training in a low load environment. The literature suggests effective training loads of 20-30% 1RM with 15-30 repetitions per set. These parameters are much more applicable to healing tissue that is not yet ready to accept more intense loads
BFR relative to ACL Rehabilitation
Early stage quadriceps dysfunction following ACL-R has implications for long term strength and performance deficits. A recent study showed a significantly strong correlation between quadriceps strength at 12-weeks post op with ultimate quadriceps strength at the time of return to sport in individuals following ACL surgery.6 This finding emphasizes the importance of early restoration of quadriceps strength during ACL rehabilitation. Blood flow restriction training can jump start the strengthening process by allowing the quadriceps muscle to train under high load conditions without causing harm to the healing structures.
Open chain knee extension following ACLR
It is now widely accepted that open chain knee extension can safely be included in the ACL rehabilitation process, but with certain parameters. It is one of the most effective ways to isolate the quadricep for strengthening and hypertrophy.
It is unclear in the literature exactly when and how much we should load open chain terminal knee extension, however the general consensus is that moderate loading within appropriate ranges offers the most effective outcomes. For more info about tensile forces and strain put on the ACL check out our recent blog post “Open Chain Knee Extension After ACL-R.”
At 2 weeks post-op we can begin to implement open chain knee extension from 90-40 degrees, depending on swelling, range of motion, and pain. Progressive resistance exercise can then be added through this range with the addition of active range of motion from 90 to 0 degrees of flexion.
It is advised that resisted open chain knee extension through 30-0 degrees is withheld till about 6-8 weeks due to the increased stress on the ACL graft. This large time frame of avoided quadriceps loading through full range of motion can contribute to further weakness with long term strength and performance implications. Blood flow restriction therapy allows for early strengthening and hypertrophy of the quadriceps without placing excessive stress on the ACL graft.
Open chain extension through 30-0 degrees of flexion also places the greatest stress on the patella femoral joint which is of higher significance for those individuals with BPTB grafts.
One literature review found that deficits in quadriceps strength following ACL-R seem to be more pronounced with BPTB autografts versus other graft types.7 This further supports the use of blood flow restriction for early quad strengthening while minimizing stress to graft and also avoiding unnecessary stress to the patella femoral joint between 30 and 0 degrees of flexion.
ACL-R with meniscus repair
Following ACL-R with meniscus repair, there can be weight bearing restrictions for up to 6 weeks. During this time frame patients are likely to experience atrophy, decreased strength, and decreased muscular endurance of the quadriceps, glutes, hamstrings, and lower leg muscles. Blood flow restriction therapy allows the patient to achieve optimal muscle activation and motor unit recruitment (type 1 and type 2 fibers), prevent atrophy, and maintain muscular endurance.
Contraindication for BFR
Contraindications related to blood flow restriction training are primarily associated with vascular insufficiencies or cardiac complications. There can be an increase in cardiac stress due to increased stroke volume and heart rate from the body trying to get arterial blood to tissues. Blood clots are also a concern regarding the use of BFR following surgery. For this reason, it is recommended that BFR is implemented around 2 weeks post-op.
One of the most important factors when performing blood flow restriction training regarding effectiveness and safety is the amount of pressure applied. We currently use the Delfi Personalized Tourniquet System which is designed to safely regulate and control tourniquet pressure for blood flow restriction applications.
Written by Hannah Sweitzer, DPT, OCS, CSCS
- Vingren, J.L., Kraemer, W.J., Ratamess, N.A. et al. Testosterone Physiology in Resistance Exercise and Training. Sports Med 40, 1037–1053 (2010)
- Julius Fink, Brad Jon Schoenfield & Koichi Nakazato (2017): The Role of hormones in muscle hypertrophy, The Physician and Sportsmedicine
- Rice DA, McNair PJ, Lewis GN, Dalbeth N. Quadriceps arthrogenic muscle inhibition: the effects of experimental knee joint effusion on motor cortex excitability. Arthritis Res Ther. 2014;16(6):502. Published 2014 Dec 10.
- David Andrew Rice, Peter John McNair, Quadriceps Arthrogenic Muscle Inhibition: Neural Mechanisms and Treatment Perspectives, Seminars in Arthritis and Rheumatism, Volume 40, Issue 3, 2010, Pages 250-266, ISSN 0049-0172
- Ferrando AA, Stuart CA, Brunder DG, Hillman GR. Magnetic resonance imaging quantitation of changes in muscle volume during 7 days of strict bed rest. Aviation, Space, and Environmental Medicine. 1995 Oct;66(10):976-981.
- Hannon JP, Wang-Price S, Goto S, et al. Twelve-Week Quadriceps Strength as A Predictor of Quadriceps Strength At Time Of Return To Sport Testing Following Bone-Patellar Tendon-Bone Autograft Anterior Cruciate Ligament Reconstruction. IJSPT. 2021;16(3):681-688
- Lepley LK. Deficits in quadriceps strength and patient-oriented outcomes at return to activity after ACL reconstruction: a review of the current literature. Sports Health. 2015;7(3):231-238