How We Use Blood Flow Restriction Training After ACL Surgery
How does BFR work? And how do we use it with our patients after ACL surgery?
A guide to BFR training, by expert physical therapists.
What is Blood Flow Restriction (BFR)?
We use blood flow restriction training for ACL rehab as soon as 1 week post-op. So, what is blood flow restriction (BFR) training?
BFR is a rehab modality that uses a tourniquet to reduce blood flow during resistance training or exercise to stimulate muscular development. Blood flow restriction with low load allows for less stress placed on the joints while still making gains in strength. More recent research suggests that BFR also helps build cardiovascular fitness and reduces pain. This is especially valuable for postsurgical, injured, or load-compromised individuals, as a way to accelerate recovery and prevent atrophy.
After anterior cruciate ligament reconstruction (ACLR) surgery, it is common to have deficits in quadriceps strength and mass, which is linked to poorer patient reported outcome measurements, functional performance, return to sport, and ACL re-injury.
We use low load BFR with our ACL rehab patients to increase quadriceps strength and mass without increasing knee joint pain or compromising ACL graft laxity, as supported by this 2022 systematic review.
How do we think BFR works? Why do we use BFR?
Blood flow restriction (BFR) partially occludes the arteries, which still allows blood flow into the extremity, but does not allow blood flow out of the extremity (since veins are now constricted). This results in less oxygen delivery to the muscles working during the exercise. You will use more muscle fibers, specifically the fibers that are known to produce force and power, when you don’t have oxygen readily available when exercising. That’s a good thing, as it allows your maximal threshold motor neurons to work while only using submaximal weight (great for somebody who can’t load their system with heavy weight yet).
Blood flow restriction (BFR) also causes a decrease in pH in the blood as a result of metabolite buildup (hydrogen, lactate, etc). This metabolite build up facilitates cellular swelling, then inducing intracellular signals that assist with muscle protein synthesis. Increases in metabolites are also known to release anabolic hormones like growth hormone (GH), insulin-like growth factor-1 (IGF-1), and testosterone, which may facilitate muscle growth as well.
Other research finds that blood flow restriction training can further facilitate exercise-induced hyperalgesia (pain relief). This study found that pain pressure thresholds in subjects who exercised with BFR cuffs on were significantly higher than when those same subjects exercised at the same intensity without BFR cuffs on.
The researchers believe that the endogenous opioid beta-endorphin, which was released during the blood flow restriction trials, may be playing a role in the reduced pain sensitivity.
This study only had 12 subjects, but the findings are very promising. We do anecdotally note that our patients complain of less pain during and after exercise when we use BFR cuffs versus when we perform the same exercises without BFR cuffs.
What is the BFR protocol for ACL rehab?
To increase muscle strength and hypertrophy:
4 sets (30-15-15-15 reps)
Using external loads of 30% 1-repetition maximum (1RM)
Interset rest periods: 30 seconds
Duration: 6-12 weeks
Frequency: 2x/week
BFR Pressures:
Personalized based on 60-80% of limb occlusion pressure (LOP)
Most recent studies used 80% LOP
LOP is the minimum pressure required to fully restrict arterial blood flow (which we would not want to do- that would be 100% occlusion)
Exercises performed in research studies: unilateral leg press, quad set, knee extension, straight leg raise
What are some exercises that we perform with BFR cuffs on?
There are many exercises that you can perform with BFR cuffs after ACL surgery. Some of the most common are glute bridges, straight leg raises with quad sets, heel raises, assisted (or unassisted) squats. We ALWAYS put cuffs on both legs, as that provides a better stimulus for muscle growth compared to only placing the cuff on the injured side.
Glute Bridge
Body Weight Squats
Single Leg Raise with Quad Set
Double Legged Calf Raises
We typically perform 4-5 of these exercises in a given training session. As stated earlier, we perform these at low intensity, but high volume (30-15-15-15) with 30 seconds rest intervals between each set. After the 4 sets of a particular exercise, we deflate the cuff and have the patient rest for 1 minute. Then we re-inflate the cuff and begin the next exercise.
You can also use blood flow restriction training (BFR) during aerobic components of the ACL rehab process. For example, we usually start with stationary biking around 4 weeks post-op. One study showed that we can use BFR cuffs at 40% of maximum arterial occlusion for 15 minutes, 3 days per week for 8 weeks to help facilitate hypertrophy (more muscle) and improved aerobic capacity in young men.
It’s important to note that these were healthy young men (not post-op ACL reconstruction) and that the sample size was 19 subjects - so take this with a grain of salt.
However, findings are promising, and we do use BFR cuffs with our patients as they cycle at 40-50% maximum arterial occlusion for 15 minutes.
How long do we use BFR cuffs in the ACL rehab process?
The research studies that tested BFR training for ACL rehab typically lasted 6-12 weeks. We use BFR in our ACL rehab for typically the first 6-12 weeks when strength training is limited by pain or poor load tolerance. We discontinue the BFR when patients are able to tolerate higher loads (>70% 1-RM) without excessive pain (>4/10 Numeric Pain Rating Scale) or swelling (>1cm knee circumference).
Closing Remarks on BFR for ACL Rehab
Overall, blood flow restriction training (BFR) is an excellent option for patients post-op ACL reconstruction. The results are clear - we should use BFR to optimize strength gains early on. When compared to progressive overload, BFR does not stack up. But early on, when the patient can’t safely load their system mechanically, we can use BFR to load their system metabolically.
This can be surgeon dependent, but we like to start using BFR cuffs as soon as 1 week post op, and typically up until 12 weeks post-op.
If you are an athlete dealing with an ACL injury, click to learn more about our blood flow restriction training program.
If you would like to work with us, contact us below to speak with a physical therapist.
Disclaimer: This is not intended to be formal medical advice. Your individual needs should be met by the appropriate health care practitioners. Please consult with a trusted provider.
Dr. Vincent Liu PT, DPT
Dr. Paul Nasri PT, DPT, OCS, COMT
Doctor of Physical Therapy
The Game Plan Physical Therapy