When you hear blood flow restricted (BFR) training, where does your mind go? Often times, it’s to a bodybuilder with a strap around his or her arm doing preacher curls. Whether you’ve tried BFR training, you’re thinking about trying it, or just want to learn more about the topic, then read on about the science behind this training style.
Blood flow restriction, or occlusion training, is a training method that’s been used for years by various athletes and coaches. It involves restricting blood flow to a limb during different forms of training and movements. For this article, we’re going to only talk BFR in regard to resistance training.
Why Do BFR Training, and How Does It Work?
The main reasoning athletes and coaches generally use for BFR training is to increase muscle size. Like with other advanced training concepts, the exact mechanisms that cause muscle size to increase during BFR training are still being researched. There are multiple mechanisms that are suggested to play a role in BFR’s benefits to muscle adaptations.
Before diving into the BFR mechanisms, it’s important to understand the premise behind its theory. Muscle growth occurs best when muscle has been damaged. As we lift and put our muscle under stress, the body responds by repairing damaged areas, making them stronger and bigger (hypertrophying). There are multiple natural responses the body uses to compensate for muscle damage, but one of the main responses linked to increased muscle repair and size is called muscle protein synthesis (MPS).
This is the body’s way of naturally repairing itself through the use of multiple anabolic mechanisms. With BFR training, there’s additional stress placed on the muscle regular training can’t induce (venous occlusion, depleted oxygen, and others). This is the theory behind using BFR to increase muscle hypertrophy (size).
A BFR training review written in 2015 suggested multiple mechanisms that might contribute to positive muscle adaptations as a result of BFR.
- Mechanical tension: The time we put our muscle under tension will facilitate growth by stimulating an increase in muscle protein synthesis (MPS).
- Metabolic stress: The rate at which a muscle becomes stressed under tension plays a role in its growth. In sum, the more we’re able to stress a muscle in a safe/practical manner, then we’ll see an increase of growth stimulating factors, which are explained more in-depth below and include: systemic hormone release, cell swelling, muscle damage, fast-twitch fiber recruitment, and reactive oxygen species.
- Mechanotransduction: In short, this is an adaptation created after mechanical tension occurs that signals mechanosensors (integrins & focal adhesions) to convert mechanical energy into chemical signals that then bring about anabolic and catabolic responses within the muscle.
- Muscle damage: The more a muscle is damaged, then the more the body will work to repair it. This point is still uncertain in regard to how much BFR causes due to its low-intensity nature.
- Systemic and localized hormones: After a muscle is under tension/damaged, then the body releases anabolic hormones in response to repair it. This is another theory that is still being researched in regard to BFR training.
- Cell swelling: As the pressure within a muscle rises from BFR, cell hydration increases. The theory as of now proposes this is due to the enhancement of protein synthesis and decrease in proteolysis (breakdown of proteins).
- Reactive oxygen species (ROS): When the muscle is increasingly taxed of oxygen, then the rate at which our body responds in an anabolic nature increases. The theory behind ROS revolves around hypoxia (deficient oxygen in tissue) and subsequent reperfusion (restoring blood flow to tissue) being heightened during BFR training.
- Nitric oxide (NO): This cellular signaling molecule is thought to be responsible for hypertrophic responses in muscle due to mechanical tension. NO production can play a role in activation and mediation of protein synthesis.
- Heat-shock protein (HSP): These are proteins released solely to maintain cellular homeostasis, which would explain their possible role in response to BFR training and the cellular stress BFR places on muscle cells.
- Type II fiber recruitment (fast-twitch): BFR has been speculated to increase type II fiber recruitment due to the inadequate oxygen supply BFR causes (a main component of type II fiber recruitment).
What Does That All Mean?
Basically, BFR training has multiple proposed reasons as to why it might work for muscle hypertrophy purposes. As we deplete the muscle’s needed resources, we increase the stress placed upon that targeted muscle. This added stress then causes an increase in natural anabolic responses by the body that normal training may not produce alone.
Research suggests keeping intensity on the lower side and often using 30-50% of one’s 1-RM to stimulate BFR response. This style of training at higher intensities can lead to more muscle damage, which should be avoided and may be counterproductive. In terms of wrap tightness, a lifter should aim to achieve a 7 out of 10 in restriction. The goal is to apply enough tightness that venous flow is occluded, not arterial.
When using this style of training it’s important to pay close attention to how your body responds. A restrictive band shouldn’t leave your limb tingling, in unbearable sharp pain, or discolored. If you find this is the case, then the band may be to restrictive, which can lead to injury. Also, BFR training can increase chance in risk of injury for hypotensive athletes, and athletes with previous blood flow issues.
Who Will It Work Best For?
Research is conflicted when it comes to the effectiveness of BFR training for muscular hypertrophy; this is largely due to the differences in methods used by study authors. There aren’t set guidelines for wrapping styles, tightness, programming, and training intensities. Also, different athletes will have varied responses due to training history, anthropometrics, and muscular profiles.
Below are a few recommendations that loosely demonstrate what research has suggested.
Beginner: May achieve some benefit, but will benefit best from simply improving their strength, mechanics, and hypertrophy with a well-constructed program.
Intermediate: May benefit the most, as this lifter has a solid muscular base, but doesn’t need as high of a training stimulus as an elite lifter.
Advanced: May not experience much benefit, as this lifter demands much more training stimulation than the 30-50% intensity will provide.
Research is still conflicted on the full reasoning behind the hypertrophy benefit BFR training causes, but there are some suggestions, which are mentioned above. Who should be using BFR training is dependent on many factors and should be considered by athletes and coaches. For those in the beginning and advanced levels of training, then they may find most benefit from a well-constructed program specific for their training needs.
Feature image from @kazanski79 Instagram page.