Blood flow restriction training after ACL injury

What is blood flow restriction?

Since successful application in wounded warriors, blood flow restriction (BFR) has been popularized in post-surgical rehabilitation for mitigating muscle atrophy. BFR involves a pneumatic tourniquet at the proximal limb that creates mechanical compression of the vasculature underneath the cuff. This external pressure results in partial restriction of arterial blood flow (ideally 40-80%) and occlusion of venous outflow from the limb. Together these effects result in muscle hypoxia, pooling of blood in the capillaries, and increased intramuscular pressure during muscle contraction.

Does blood flow restriction work?

High-load resistance training is better than BFR

Before we begin. The bottom line is this:

If your patients/clients can tolerate high-load resistance training, skip BFR. High-load resistance training is consistently better than BFR at building hypertrophy and strength.

With high-load resitance training healthy populations -- i.e., 80% 1-RM 3x/week for 6 weeks -- in general, we can expect 6% increase in muscle size and 22% increase in strength.

With low-load resistnce training with BFR -- i.e., 20-40% 1-RM 3x/week for 6 weeks -- in general, we can expect 5% increase in muscle size and 12% increase in strength.

Where BFR really shines, is when our patients cannot tolerate high-loads. Scenarios such as early post-injury or post-surgery, when arthrogenic muscle inhibition is present, are perfect. By using BFR, we can drive more effective training sessions by using low-loads with BFR compared to low-load training alone.

Blood flow restriction after ACL reconstruction.

A systematic review in IJSPT (Charles et al, 2020) included four randomized controlled trials using BFR early after ACL reconstruction. The results are rather consistent showing better strength and preservation of muscle mass for individuals using BFR training compared to low-load resistance training alone.

Jack et al, recently published in Sport Health showed a LARGE preservation effect in terms of lean muscle (muscle mass) in the involved limb compared to control groups. Essentially, the involved thigh of the no-BFR group had 5% less muscle mass at 3 months than they did at baseline, where the BFR group was normal. (note: 0% is pre-op mass, not pre-injury mass).

Sets and reps are shown in the figure caption and can be weighed against the recommendations our user guide.

Does blood flow restriction address arthrogenic muscle inhibition?

How does it work?

Blow flow restriction works through two main mechansims: 1) mechanical tension of muscle fibers (think: lifting heavy weights) and 2) metabolic stress. By applying a partial tourniquet to the limb, venous pooling and intramuscular tension allows patients to achieve high levels of mechanical tension during low-load exercise (20-40% 1 rep max [1RM]). In parallel, increased levels of metabolic stress drive systemic hormone production and fast-twitch (anearobic) muscle fiber recruitment. Together, these stimuli promote gains in muscle hypertrophy and strength despite training with low-loads. (Pearson and Hussain, Sports Med, 2015)

Does it address muscle inhibition?

Not directly. Neural inhibition persists, but BFR does encourage selective activation of high-threshold fast-twitch muscle fibers. This means effects similiar to high-training loads despite low-resistance in rehabilitation -- albiet inhibited muscle fibers theoretically remain unrecruited. I wonder what would happen if we combined this with cryotherapy?!

Blood Flow Restriction User Guide

We’ve put together a user guide for our subscribers. It explains set-up, exercise prescription, and risks and considerations of using BFR. You’ll also get access to our other science-meets-practice content. Check it out.