Contrary to my typical monologues, let's get straight to the point today because we have a lot to cover...
Blood flow restriction, occlusion training, Kaatsu method; all of these titles refer to the same novel technique that has been (somewhat) revolutionary in our understanding of how hypertrophy works.
For decades, we approached training with the simple assumption that forcing our bodies to handle more volume load over time would lead to positive muscular and strength adaptations. And this turned out to be a really fruitful assumption as the concept of progressive overload has become the backbone of training methodology and periodization. All of this is predicated on the model of myofibrillar hypertrophy (i.e. adding structural units to the sarcomeres that make them capable of producing more force) which is the dominant way in which muscles grow.
It wasn't until more recently that exercise physiologists started to put the pieces together on another mythologic model: sarcoplasmic hypertrophy.
Every person who has knocked out a set of 20 biceps curls understands that something special happens when tons of blood gets trapped in a compartment without the necessary volume to support it...
Skin-splitting, shirt-tearing, head-turning, ego-inflating PUMPS!!!
For much of the history of structured training, we thought that the "pump" was more of a byproduct rather than an effect that was directly contributory. It was always great to walk away from the squat rack with quads consuming your kneecaps, but the overloading sets of squats were still meant to be the primary focus. This all changed when it became understood that there were real physiological effects that lent efficacy to forcing as much blood as possible into a working muscle.
At a high level, sarcoplasmic hypertrophy is just fancy talk for increasing the volume of our muscle cells. Whereas, myofibrillar adds those contractile units to make the cells more dense, sarcoplasmic expands the cell with more fluid and "non-contractile" units. By getting tons of blood in a working muscle, we can actually induce this mechanism of hypertrophy independently of mechanical tension and progressive overload.
In addition to the increased blood flow, certain metabolites and byproducts of muscular contractions, as well as hypoxia, stimulate receptors in and on the muscle cells that "turn on" anabolic pathways. This is much more abstract than simply lifting heavy weights which is why it took so long for scientists to conclusively prove these theories. But the complexity doesn't detract from effectiveness; metabolic stress deserves a solidified place alongside mechanical tension as a mechanism for inducing hypertrophy.
Now this is where blood flow restriction (henceforth, "BFR") really shines!
Shifting the primary focus away from overloading and towards metabolite work requires real tact and skill in program design. Obviously, the lowest hanging fruit is to increase rep ranges and decrease absolute loads, but we have MANY other vectors by which we can take advantage of this new environment such as shortening rest times, liberally including supersets, and adding in novel movements. Once these bases have been covered, BFR can be the cherry on top.
So what is it?
BFR is the act of restricting venous return of blood from a working muscle. By allowing blood to flow in but not back out, we essentially trap all of those aforementioned metabolites and byproducts along with the blood volume. This creates a honeypot of paracrine signaling and cell swelling that sustains for as long as the trainee can tolerate the increasingly acidic local environment. The end effect is a massive sarcoplasmic hypertrophy stimulus.
How to do it?
This is typically done with an elastic wrap or tourniquet of some sort. The wrap will be applied to the most proximal aspect of the appendage (note: this only works with muscles like the biceps, triceps, hamstrings, quads, etc) and applied with a 7/10 tightness in order to allow arterial flow in. Make sure you can still contract the muscle normally and without obstruction.
Prescription can vary but the goal should be to get as much density of volume in with lighter than normal loads. 20-30% of 1RM will generally suffice. Clinically, 4 sets of 30/15/15/15 separated by 30 sec rest is often the standard, but in the real world, I've found it much more practical to just aim for as many reps as possible in a given time limit.
How often to implement it?
This is the complicated part and is dependent on what BFR is being used for. When attempting to work around injuries or stave off atrophy, adaptation and down-regulation aren't of primary concern. BFR can be leaned into as needed until more load-bearing activities can resume. But in the case of a healthy trainee, we should be cautious to not overuse BFR. Much like metabolic work in general, our bodies will find homeostasis much faster than with progressive overload. Strategically cycling BFR in every 4-6 months for 3-5 weeks is a really great way to ensure that it remains a novel stimulus when used and sustains the hypertrophic effects we're after.
For years, BFR has been one of my favorite techniques to use on myself and my clients. I've found the potential use-cases to be essentially limitless. However, there are some risks associated with BFR; I would recommend anyone who is interested in trying this out make sure that they fully understand these contraindications. For those who are good candidates and slightly masochistic, give BFR a try and see just how high your pain threshold truly is!