What is Blood Flow Restriction (BFR)?

More Importantly, How Does it Work and in What Contexts?

by Campfire Coach Accelerator Adam Goulet, DC, MS, CCSP, CSCS

Only BFR with a trained supervisor!

“What would have become of Hercules… if there had been no lion, hydra, stag or boar – and no savage criminals to rid the world of? What would he have done in the absence of such challenges? Obviously he would have just rolled over in bed and gone back to sleep. So by snoring his life away in luxury and comfort he never would have developed into the mighty Hercules. And even if he had, what good would it have done him? What would have been the use of those arms, that physique, and that noble soul, without crises or conditions to stir into him action?” – Epictetus

One beautiful aspect of endurance sports is that one can continue improving at them for years. The question always remains, though: how? How do you continue to improve physically and psychologically? How can you always nudge the needle onward? Maybe you’re already consistent in your training, and you tackle every day as a chance to improve upon the day before. If you’re already doing the hard work of staying consistent, then the place to look is the changes you can make in your offseason.

If we are tackling endurance full-throttle during our season, then the offseason is not “off.” Your time away from in-season training is a time to improve the aspects of our performance that we cannot address within the race season. This is a great time to work on nutrition, cross-training, and strength training. The latter is an often overlooked piece of the endurance puzzle, and I’ll try today to provide some ideas that address strength in general. Specifically I’ll examine how best to implement blood flow restriction (BFR) training into the endurance paradigm. That raises an immediate question: what the heck is BFR?

BFR is a subset of strength training that uses a tourniquet to physically restrict the blood flow into a limb. Why in the world would you want to do that? To answer that question we need to address the place of strength training in an endurance program more broadly. Strength training can be an integral part of year-to-year improvement and, due to the increased stress on the body both neurologically and muscularly, it is most often programmed in the offseason. There are two major reasons why strength training can improve performance. The first and more obvious reason is that strength training can increase the size of your muscles, and bigger muscles generally result in increased muscular strength. As this relates to endurance performance the stronger your muscles become the more powerfully they can press on a crank or push off the ground. Increasing muscular strength is akin to being able to go faster. However, due to some pretty interesting physiology, this is a hard task to achieve while also doing endurance training. Building muscle mass is incredibly resource-intensive for your body and unless specifically supported with the correct stimulus, nutrition and recovery it is something your body does not generally like to do. The second primary reason strength training can be beneficial for athletes is that it improves neuromuscular integration between the nervous system and the muscles. By challenging the body's ability to integrate the nervous system with the muscles (done through intensive loading) we can increase the force produced by muscles, increase  core strength and stability, and improve dynamic coordination between multiple body regions (arms and legs). While an endurance athlete due to aerobic stimulus is unlikely to receive the benefits of increased muscle mass, what we can achieve with  intensive strength training is improved core stability and coordination resulting in increased power output, and faster times come race season. 

How does BFR fit into this picture? By reducing the blood flow to the working muscles, BFR will cause your muscles to have to work anaerobically, which increases the rate at which the muscles fatigue. As your muscles fatigue doing a movement, let’s say a knee extension, your body has to recruit more and more of the muscle to make the movement happen. That is to say, when you do a normal knee extension your body will use the least amount of muscle possible to achieve that movement; as you fatigue you recruit more muscle fibers to achieve the same movement. By employing BFR you can “skip” some of the unfatigued part and get straight to the moment in which you have to recruit new muscle fibers

Some of your movements will be bodyweight only—less load!

Along with the increased muscle fiber recruitment and higher rate of fatigue, your nervous system has a harder and harder time telling your muscles to contract. This difficulty means that as you go through a BFR session you will need to produce a higher nerve stimulus to produce the same effect (the lifting of the weight). In the end, because BFR recruits larger numbers of muscle fibers/motor units, and makes your nervous system work hard (increased demand on your neural drive), your muscles become stronger. 

Additionally, the anaerobic process inside the muscle that happens during a BFR session produces metabolic changes that increase the rate of muscle growth and recovery. Here’s the beauty thought BFR is very low load. Because you are reducing the blood flow to the muscles and performing an exercise over several minutes (7-15 minutes typically) the amount of load or weight you can lift needs to be very low, in fact for some cases even body weight may be too much load and assistive exercises may be appropriate. The takeaway? BFR can result in increased strength with very low loads during strength training. 

Wait, you heard me say blood flow restriction, isn’t that dangerous? It absolutely can be. BFR should only be done under the supervision of a professional. There are many different systems out there for BFR, and, simply put, if you can buy it on Amazon, it’s probably a bad idea. A safe and effective BFR protocol should use a wide pneumatic tourniquet (like a blood pressure cuff); it should have some sort of monitoring system that both can inflate and deflate the tourniquet as you move to maintain a constant PSI within the tourniquet; finally, an effective and safe BFR system will measure a personal tourniquet pressure (PTP) for you, which typically is 60-80% of what a blood pressure cuff might use to take your blood pressure. If you find yourself being offered a BFR system or workout that does not meet these criteria, but rather uses elastic cuffs or a hand pump to inflate a tourniquet, then run: those systems do not have reproducible results and can be unsafe. One more time for the people in the back! Don’t use BFR without professional supervision.

Now that we have cleared that hurdle, let’s talk about the amazing advantages to BFR. First, endurance athletes are time crunched by nature. BFR training, due to the fact that it reduces blood flow to the muscles and asks you to perform an exercise over several minutes (seven to fifteen, usually), uses much lower loads than you normally would in a traditional gym session. In some cases even body weight is too much and assistive exercises may be appropriate. Due to those lower loads and increased metabolic fatigue, you actually decrease the strain placed on your body. The magic is that you can improve strength at lower load. The number one reason we get hurt while strength training is that we use weights, bands, and cables at too high a load. BFR reduces that load dramatically and can therefore reduce injury risk. Because the loads we are using for a given exercise are lower with BFR (someone who can squat 300 pounds, for example, may only squat 30 during BFR), the exercise is less likely to create soreness. 

Here, however, is the biggest benefit: BFR is hard, really hard, but because of that difficulty this type of training exposes motor imbalances and functional deficits. This exposure means that if you have a compensation pattern that only bothers you when you’re fatigued (like your knees drop in towards each other at the end of a long run) you will see that happen in a BFR session. BFR, therefore, gives us a golden opportunity to address compensations which we may never see in a normal strength training session. Along those lines, one of the most common dysfunctions we all have is coordinating breathing with lower body movements. BFR is hard, like an anaerobic sprint. This fact means it will make you breathe hard and provide us an opportunity to fix our core, breathing, and movement patterns. This type of repair is extraordinarily hard to do in normal circumstances. Can you imagine your coach asking you to run for two hours simply to address the form deficits that arise with fatigue? BFR also has the potential benefit of consolidating and preserving strength gains through the competition season  with as little as two fifteen-minute sessions a week. 

Finally, from a psychological standpoint BFR provides us with a chance to go hard and dig deeper than we thought we could without wrecking our bodies. There is benefit in finding a new level of effort and going harder than you thought you could, but in a race or workout that high level effort could take a week or more to recover from. The low loads of BFR mean you can exercise the power of your mind fully and repeatedly without having to worry about how long it takes to recover. BFR is innately an anaerobic stimulus and should be considered as such. While BFR can have some aerobic benefits including increased mitochondrial mass, it should be made very clear that as with all workouts, dose and recovery are key to getting an optimal response. The longest BFR protocols typically do not exceed 15 min, and within that time frame a maximum of 30 reps at a time is standard; the intent of BFR is to get the most bang for your buck, with this in mind a BFR session asks you to give maximal effort, while keeping loads very low. This is to say that there is no benefit to trying exercises that are aerobic in nature with BFR, the resulting stimulus would be null, and aerobic work is generally a misappropriation of BFR training. It is plausible that you could use BFR with a certified professional on a stationary bike or treadmill, however the exercises performed in those cases are not aerobic. BFR, when used appropriately can be an amazing adjunct to training, and with supervision increases in muscle strength, nervous system integration, and dynamic coordination can all be achieved with very little negative effects of muscle soreness. However, as with many training modalities inappropriate programming and use of BFR can be detrimental to performance and at worst dangerous.