Anterior cruciate ligament (ACL) rupture is a highly prevalent orthopedic injury, with over 120,000 injuries occurring each year in the United States. Rehabilitation timeframes are typically between 6 and 12 months with many sufferers encountering muscle atrophy, strength loss, joint effusion and arthrogenic muscle inhibition. ACL repair represents one of the most studied orthopedic injuries and thus rehabilitation techniques have evolved over several decades. Blood flow restriction (BFR) training is rapidly emerging as a viable strategy at multiple stages of ACL rehabilitation and is widely considered an integral part of gold-standard ACL injury management. The use of BFR in ACL management was first explored over 20 years ago as a passive strategy to minimize muscle loss in the first 2 weeks post-surgery (Takarada, 2000). Since then, interest in BFR as a rehabilitation strategy has grown exponentially, and more research has sought to explore the use of BFR in a progressive model through all stages of rehabilitation from pre-surgery conditioning, right the way through to a return to sporting performance.
The aim of this blog is to provide a framework for BFR to be used as a part of a holistic and progressive management strategy, across the various stages of ACL rehabilitation.
Stage 1 - Stronger in = Stronger out:
Rehabilitation following ACL surgery can begin even before the surgery has started. Increasing lower limb muscle strength prior to surgery is believed to attenuate the deterioration of muscle mass and function in the aftermath of invasive surgery. The adequately named “preconditioning” program presents a unique challenge to deliver an exercise stimulus sufficient to increase muscle mass without exacerbating effusion and pathology in a joint that has suffered significant trauma. A recent randomized controlled trial explored the use of a BFR intervention in the 10 days prior to ACL reconstruction surgery on maximal muscle strength, muscle endurance, surface EMG and muscle blood flow (Zargi et al 2018). As few as 5 BFR exercise sessions were completed, and resulted in significant improvements in muscle endurance, muscle activation and blood flow within the first 4 weeks after ACL reconstruction. These findings demonstrate that a short-term BFR training program may be a valuable addition to standard rehabilitation programs for patients elected for ACL reconstruction surgery. This protocol used a high volume set and rep scheme (3x sets to volitional failure), combined with a low training intensity (40 repetition maximum) and a high absolute pressure (150mmHg with a wide cuff). These variables suggest that biasing the programming variables to achieve a high level of metabolic stress may be an effective pre-surgery strategy to achieve sustainable change in muscle endurance and activation.
Stage 2 – Post-operative care - How early can you start?
Within the confines of a clinical research facility, the use of BFR has started as early as 2-days post-surgery. The objective of this phase is preventing muscle disuse atrophy and strength loss, minimizing joint effusion and pain management. Passive application of BFR can stimulate muscle protein synthesis and has been shown to minimize muscle atrophy when applied as soon as 2-days post ACLR surgery. The most common protocol is 5 sets of 5 minutes occlusion with 2-3 minutes of rest. Higher occlusion pressures, perhaps full limb occlusion (100% LOP) may be required to provide a sufficient stimulus to trigger muscle adaptation. Combining passive BFR with neuromuscular electrical stimulation has also been shown to be an effective strategy to increase muscle mass in post-traumatic knee injury. Three papers have thus far explored the use of BFR within the first 10 days post-ACL surgery and have not reported any incidence of an adverse event or contraindication (Takarada et al 2000, Iversen et al., 2016, Prue et al., 2020). Prue et al (2022) implemented BFR + LI resistance exercise intervention at 9 days post-surgery and reported a small number of episodes of dizziness, paraesthesia and itching.
In an applied setting, many practitioners will avoid the use of BFR in the early stages post-surgery amid fears of an increased risk of a thromboembolism and anecdotal concerns about exacerbating acute joint effusion. While there is little evidence substantiating these concerns when BFR is used appropriately (initial evidence suggests BFR training may reduce joint effusion post ACL surgery), Hughes et al. (2019) proposed a criteria-based assessment to commence the use of BFR training post-surgery. This list included a return to basic muscle function and joint health demonstrated by:
- Unilaterally weight bear without pain for >5s without support
- Demonstrate knee ROM of 0-90 degrees.
- Perform repeated straight leg raises without quadriceps muscle lag.
- Minimal effusion changes with activity.
Stage 3 - Regaining muscle size and strength:
Perhaps the most common use of BFR training is in combination with low-intensity resistance exercise to target improvements in muscle mass and strength during early-stage re-loading. The benefits of BFR combined with resistance exercise are well documented, with improvements in muscle hypertrophy being comparable to heavy traditional resistance exercise, and improvements in strength superior to an exercise matched control. When compared traditional rehabilitation strategies like high-intensity resistance exercise, BFR combined with LI-RT has resulted in:
- Greater improvements in joint pain, range of movement, self-reported knee function and knee extensor muscle torque
- Comparable improvements in muscle mass and repetition maximum muscle strength.
When compared to an exercise-matched control group, BFR combined with LI-RT has resulted in:
- Greater improvements in quadricep muscle cross-sectional area, knee extensor and knee flexor muscle torque.
Programming within this phase should be consistent with principles of progressive overload and specificity. Metabolic stress and mechanical load should be systematically increased through changes in limb occlusion pressure/time under occlusion and intensity respectively. Training loads between 20-40% 1RM combined with cuff pressures between 40-80% LOP are recommended for improvements in muscle strength and hypertrophy.
Get back on track
Chronic muscle atrophy and strength loss:
After ACL reconstruction many individuals do not completely regain quadriceps size and muscle strength. Persistent quadriceps asymmetries predispose individuals to altered joint loading and gait mechanics, limited physical function and joint, increased risk of re-injury, and early onset of osteoarthritis. Long-term strength deficits are often associated with other signs of joint pathology and therefore regaining muscle size and strength can pose a significant challenge. Recent research from Kilgas et al (2019) explored a home-based BFR intervention in individuals with persistent muscle atrophy and strength deficits 5 years post-ACL reconstruction. Within the study a 4-week BFR intervention resulted in a ~10% increase in quadricep muscle mass, and a 20% increase in knee extensor muscle torque, while returning the limb symmetry index to 99±5% across all markers. Further research from Noyes et al (2021) explored this concept across various post-surgical patients including total knee replacements and meniscus repairs, alongside ACL reconstruction who were on average 5.3 months post-surgery. In this prospective study, patients had undergone ~5 months of traditional rehabilitation and presented with persistent strength deficits in the quadriceps (43%) and hamstrings (38%). After 6 weeks of BFR training most patients experienced improvements in muscle torque by >20% in both muscle groups.
The use of BFR training has now become commonplace in the management of ACL reconstruction rehabilitation. As we learn more about the practical implications of BFR training, and the mechanisms through which BFR influences the neuromuscular and skeletal muscle systems, we identify more potential use-cases throughout the ACL rehabilitation journey. Further research is still required to fully explore the efficacy of BFR as a rehabilitation strategy, however with 20+ years of research and 30 peer-reviewed publications, the initial evidence is too promising to ignore. Practitioners are encouraged to establish clarity in their purpose when implementing and programming BFR into their rehabilitation protocols and have clear systems in place to track progress and monitor for setbacks.
- Takarada, Y., et al., Applications of vascular occlusion diminish disuse atrophy of knee extensor muscles. Medicine & Science in Sports & Exercise, 2000. 32 (12): pp 2035-2039.
- Zargi, T., et al., Short-term preconditioning with blood flow restricted exercise preserves quadriceps muscle endurance in patients after anterior cruciate ligament reconstruction. Frontiers in Physiology, 2018. 9: pp 1-13.
- Prue, J., et al., Side Effects and Patient Tolerance with the Use of Blood Flow Restriction Training after ACL Reconstruction in Adolescents: A Pilot Study. International Journal of Sports Physical Therapy, 2022. 17 (3): 347-354.
- Iversen, E., et al., Intermittent blood flow restriction does not reduce atrophy following anterior cruciate ligament reconstruction. Journal of Sport and Health Science, 2015. 5: pp 115-118.
- Hughes, L., et al., Comparing the Effectiveness of Blood Flow Restriction and Traditional Heavy Load Resistance Training in Post-Surgery Rehabilitation of Anterior Cruciate Ligament Reconstruction in Patients: A UK National Health Service Randomised Controlled Trial. Sports Medicine, 2019. 49: pp 1787-1805.
- Kilgas, M. A., et al., Exercise with Blood Flow Restriction to Improve Quadriceps Function Long After ACL Reconstruction. Training and Testing, 2019. 40: 650-656.