In 2015, I saw our strength coaches tie their arms up with bands, cut off their blood flow, and knock out some curls.
I had no clue what they were doing, but they looked way more jacked than I’d ever seen them before.
So, naturally, as a self-proclaimed meathead, I asked them to tie my arms up after our session that day.
The pump had me hooked.
I talked to all the PTs, strength coaches, and exercise science professors I could about it.
They thought our coaches were crazy and assured me my arms would fall off.
Years later, during one of my clinical rotations, I saw a nationally renowned company slap the same straps on every patient with a pulse and an injury that walked through their doors. They just had fancier machines.
How did cutting off blood flow to someone’s limbs go from taboo bro science to mainstream medical use?
Let’s talk about blood flow restriction training and why it might not be what everyone thinks it is.
What is it?
Blood flow restriction training (BFR) is the process of using inflatable cuffs or wraps to partially restrict blood flow to a limb during exercise. It’s also referred to as occlusion training or Kaatsu training.
Why does it matter?
The textbooks always tell us that you need to lift a weight that’s at least 65-70% of your 1-rep max (1RM) in order to get any gain in muscle mass (which is called hypertrophy) or any gain in strength.
But, what if you can’t load up that heavy for some reason? What if you have a recent injury or surgery? Do you just sit around and let all your muscle mass and strength blow off into the wind while you take the time to rehab your injury?
The corny rhetorical question is a dead giveaway that no, that’s not the solution.
BFR has demonstrated the ability to increase muscle size and strength at rates similar to heavy load strength training, while only using low loads (as low as 20-30% 1RM).1, 4, 6, 7, 8, 9
These low loads are safe to use in many early stage rehab situations.
This article’s going to focus on hypertrophy (muscle growth) and strength, but BFR might have some other valuable benefits relating to pain, recovery, and aerobic improvements.
How does it work?
There are some really cool, super in-depth, complex theories that have been investigated about how BFR training works.
But, at the end of the day it looks like simplicity wins again.
The main reason BFR helps to gain muscle mass and strength is through acclerating fatigue.
Essentially, waste products (metabolites) build up quickly and create an oxygen-deprived (hypoxic) environment.
The hypoxic environment results in the muscle getting tired quicker with lower loads.
This fatigued environment replicates the same responses that grow muscle in the last couple reps of a heavy set.
So, instead of needing to load up heavy weights or do a million reps with a light weight, you can gain muscle mass and strength with light loads and (relatively) low reps.
The mechanisms that BFR training stimulates muscle to grow are the same mechanisms that regular training stimulates muscle to grow.
These will be covered in depth in their own newsletter in the future, but for now I want to stick to the basics and how they are specific to BFR training.
Mechanical tension → cellular signaling pathways
When a muscle is working very hard, there is a lot of mechanical tension (how hard the fibers are pulling and being pulled) that is placed along the muscle fiber.
We have cells in our body that detect changes in muscle shape through tension. These are called mechanoreceptors.
These mechanoreceptors trigger a series of chain reactions among other cells that cause muscles to grow. We refer to this chain reaction as an anabolic signaling cascade. (The pathways are turning up mTOR and turning down myostatin2,5,6,7,8,9, if you’re curious to search more).
These mechanoreceptors are stimulated when there is a high amount of force and the muscle is contracting slow.
The combination of those two factors (high force and slow speed) can only occur when a muscle is reaching failure.
Blood flow restriction training decreases the amount of time that it takes for the muscle to reach that failure point, by preventing blood flow from clearing out the waste products that build up.
Fiber type recruitment
We have two main categories of muscle fiber types. (In reality, they exist on a continuum, not in categories. But, it’s simple and accurate enough for the context of this article).
Type 1 muscle fibers are slow twitch and are good for endurance.
Type 2 muscle fibers are fast twitch and are good for strength, speed, power, and hypertrophy. Type 2 muscle fibers are not good at working for a long period of time.
Our nervous system wants to be as efficient as possible, so when we start lifting a weight, we only use the smallest amount of muscle fibers needed. We recruit the slow twitch fibers first.
As the demand goes up, or as the other muscle fibers start to fatigue, we move on to recruit bigger and bigger muscle fibers. This is a part of a concept called Henneman’s size principle.
Type 2 muscle fibers are the ones that we want to recruit to get hypertrophy and strength gains, but they’re the last ones to join the party.
BFR speeds up that process by fatiguing out the other muscle fibers quicker. This allows us to recruit the bigger Type 2 muscle fibers with lower loads and/or less reps than would otherwise be needed.2,7,8,9
Hormonal response
Hormones control a lot of things, like dumb decisions made by teenage boys trying to impress some girls and how much stress radiates through our house once a month when my wife is magically not-so-happy anymore..
When it comes to muscle and strength development, we’re looking for hormones that are anabolic (which means to build up), as opposed to catabolic (which means to break down).
More specifically, we want hormones that promote muscle protein synthesis. Muscles are made up of protein, so creating more muscle protein results in bigger muscles.
The 3 main hormones that fit the bill are growth hormone, IGF-1, and testosterone. Here’s the BFR related quick-summary for each.
Growth hormone (GH)
There’s a big debate on whether growth hormone even results in muscle growth at all.
Blood flow restriction training definitely increases GH levels for a short period of time after exercise.2,12
There’s some evidence to suggest that GH secretion is greater with BFR training than non-BFR training12, but those short-term increases don’t actually result in greater muscle mass or strength gains.4
IGF-1
Quick and simple: IGF-1 is a hormone that is associated with muscle mass and strength gains, but the research on the role BFR plays here is conflicted and a toss-up.2
Testosterone
Testosterone is the gold-standard hormone for getting jacked and strong (which is why anabolic steroids are banned in professional sports).
However, BFR training doesn’t seem to have any significant impact on testosterone levels.12
Bummer.
Hormones as a whole
As a whole, it doesn’t seem like short-term increases in hormone levels result in changes in muscle size or strength.4
Being that there isn’t a lot of evidence to support long-term hormonal changes with BFR training, it’s safe to assume that the hormonal responses aren’t playing a big role in muscle mass and strength gains.
How can I use it?
FINALLY, the important stuff.
While the above sciencey jargon is complicated and confusing, the use-cases are straightforward.
BFR can and should be used in situations where high loads cannot be tolerated or are contraindicated.
Think early stage post-op or acute conservative rehab.
If you have a post-op ACL patient, you have to protect the graft and avoid loading too crazy too quickly.
But, that doesn’t mean you can’t challenge the heck out of that muscle with some low loads and BFR. The more muscle we can keep/gain early on, the better off they’ll be later on.
Same thing goes for someone you’re rehabbing from patellofemoral pain. If we can get that quad strong without putting too much stress on the joint itself, that’s a big win.
The protocol that everyone and their mother uses is 4 sets with 30 seconds rest between each set: x 30 reps, x 15 reps, x 15 reps, x 15 reps.
That’s not a magic potion recipe that you have to follow verbatim, but it works well.
It stems from some original research that showed people usually got about 75 reps in when they did 4 sets to failure.
So, they split those reps up into organized sets.
The only thing that really matters is that you take the muscle to fatigue and force it to strain.
My thoughts
BFR is tough.
It feels weird and quite uncomfortable, especially the first few times you do it.
For the general population, that’s usually a turn-off.
For athletes, though, it’s a bonus.
Athletes usually like to embrace the suck. They are used to grueling practices and feeling challenged.
Early stage rehab is often ridiculously boring for them.
Using BFR is beneficial if for no other reason than it keeps them engaged and challenged.
Keeps athletes feeling like they’re going through something really rigorous
BFR evidence is messy
I won’t lie, sifting through BFR research to put this together wasn’t a particularly fun endeavor.
BFR research is like a minefield right now. There are a ton of studies, but many of them are garbage.
There are also a lot of one-off studies that have contrarian results.
It would be quite easy to cherry-pick evidence to fit a narrative, which I’m sure many involved in the product side of this field will do.
Try not to get lost in the sauce with all of it.
Remember the North Star is “accelerating fatigue.” It’s not some biological cheat code..
Fun facts
BFR probably doesn’t create strength gains as well as it creates hypertrophy
This is more important than something usually relegated to the “Fun facts” section, but I wasn’t sure where else it fit best.
It’s clear that you can get strength and hypertrophy gains from BFR training.
It’s also pretty clear that the hypertrophy gains from BFR low load training are pretty dang similar to hypertrophy gains from regular high load training.
However, it seems that the strength gains from BFR low load training aren’t nearly as equal to heavy load training.
Taking a step back, this actually makes a ton of sense.
Strength isn’t just a muscle driven physical quality. It’s a skill.
To get all of the component systems as efficient as possible (nervous, connective, muscular), you need to practice that skill.
The best way to get better at lifting heavy weights is to lift heavy weights.
You could get the same exact results with the same low loads, without BFR.3,11
In fact, you can actually get the same level of hypertrophy with low loads to failure as you can with high loads to failure.10
The caveat here is that you would need about a billion more reps (give or take a few) in order to reach the failure point that initiates the anabolic cascade.
Most people don’t have the mental fortitude, level of attention, and high enough training age to actually push through the time that it would take to truly get to failure with those low loads without BFR.
That’s it!
Just a reminder, if you’re going to cut off some blood flow, do it under the guidance and supervision of a qualified healthcare practitioner.
Best,
Zach
Dr. Zach Guiser, PT, DPT, CSCS
References:
1. Wortman RJ, Brown SM, Savage-Elliott I, Finley ZJ, Mulcahey MK. Blood Flow Restriction Training for Athletes: A Systematic Review. Am J Sports Med. 2021 Jun;49(7):1938-1944. doi: 10.1177/0363546520964454. Epub 2020 Nov 16. PMID: 33196300.
2. Hwang PS, Willoughby DS. Mechanisms behind blood flow-restricted training and its effect toward muscle growth. Journal of Strength and Conditioning Research. 2019;33:S167–S79. Pmid:30011262
3. Pavlou K, Korakakis V, Whiteley R, Karagiannis C, Ploutarchou G, et al. (2023) The effects of upper body blood flow restriction training on muscles located proximal to the applied occlusive pressure: A systematic review with meta-analysis. PLOS ONE 18(3): e0283309. https://doi.org/10.1371/journal.pone.0283309
4. Blood-Flow-Restriction-Training-Induced Hormonal Response is not Associated with Gains in Muscle Size and Strength. By: Laurentino, Gilberto C., Loenneke, Jeremy P., Ugrinowitsch, Carlos, Aoki, Marcelo S., Soares, Antonio G., Roschel, Hamilton, Tricoli, Valmor, Journal of Human Kinetics, 16405544, 20220901, Vol. 83, Issue 1
5. Schuelke, M., M.D., Wagner, Kathryn R,M.D., PhD., Stolz, L. E., PhD., Hübner, C., MD, Riebel, T., M.D., Kömen, W., MD, . . . Lee, Se-Jin,M.D., PhD. (2004). Myostatin mutation associated with gross muscle hypertrophy in a child. The New England Journal of Medicine, 350(26), 2682-8. Retrieved from http://wa.opal-libraries.org/login?url=https://www.proquest.com/scholarly-journals/myostatin-mutation-associated-with-gross-muscle/docview/223940890/se-2
6. Laurentino GC, Ugrinowitsch C, Roschel H, et al. Strength Training with Blood Flow Restriction Diminishes Myostatin Gene Expression. January 2012. doi:10.1249/mss.0b013e318233b4bc
7. Pearson SJ, Hussain SR. A Review on the Mechanisms of Blood-Flow Restriction Resistance Training-Induced Muscle Hypertrophy. SPORTS MEDICINE. 2015;45(2):187-200. doi:10.1007/s40279-014-0264-9
8. Grønfeldt BM, Lindberg Nielsen J, Mieritz RM, Lund H, Aagaard P. Effect of blood‐flow restricted vs heavy‐load strength training on muscle strength: Systematic review and meta‐analysis. Scandinavian Journal of Medicine & Science in Sports. 2020;30(5):837-848. Accessed April 5, 2023. https://search.ebscohost.com/login.aspx?direct=true&db=s3h&AN=142704986&site=eds-live
9. Lixandrao ME, Ugrinowitsch C, Berton R, et al. Magnitude of muscle strength and mass adaptations between high‐load resistance training versus low‐load resistance training associated with blood‐flow restriction: a systematic review and meta‐analysis. Sports Med (Auckland, NZ). 2017 ; 48 (2): 361 ‐ 378.
10. Schoenfeld, Brad J.1; Grgic, Jozo2; Ogborn, Dan3; Krieger, James W.4. Strength and Hypertrophy Adaptations Between Low- vs. High-Load Resistance Training: A Systematic Review and Meta-analysis. Journal of Strength and Conditioning Research 31(12):p 3508-3523, December 2017. | DOI: 10.1519/JSC.0000000000002200
11. Yasuda T, Fukumura K, Iida H, Nakajima T. Effect of low-load resistance exercise with and without blood flow restriction to volitional fatigue on muscle swelling. Eur J Appl Physiol 115: 919–926, 2015.
12. Reeves GV, Kraemer RR, Hollander DB, Clavier J, Thomas C, Francois M, Castracane VD. Comparison of hormone responses following light resistance exercise with partial vascular occlusion and moderately difficult resistance exercise without occlusion. J Appl Physiol (1985). 2006 Dec;101(6):1616-22. doi: 10.1152/japplphysiol.00440.2006. Epub 2006 Aug 10. PMID: 16902061.