What is blood flow restriction training? In essence, this training method is exactly what it sounds like: limiting blood flow to muscles while training. This is usually done by using specialist equipment, such as blood flow restriction (BFR) cuffs.
What has grabbed people’s attention is its reported benefits, with claims BFR can stimulate impressive muscle growth and strength gains from resistance training with a lower load.
It has also been suggested that BFR could be used during low intensity, aerobic activities – such as a session on one of the best walking treadmills (opens in new tab) – to prevent atrophy or muscle loss in deconditioned people, such as elderly populations and those with an injury.
To separate fact from fiction, we spoke to Jeremy Loenneke, an associate professor of exercise science at The University of Mississippi, and an authority on blood flow restriction training.
Jeremy Loenneke is the director of the Kevser Ermin Applied Physiology Laboratory at Mississippi University and his research group’s primary focus is on skeletal muscle adaptations to exercise with and without the application of blood flow restriction. He is a Fellow of the American College of Sports Medicine and a member of the American Physiological Society.
What is blood flow restriction training?
As outlined above, BFR involves restricting blood flow to a muscle that’s currently being worked. Loenneke offers this summary. “Blood flow restriction training involves applying a cuff or wrap on the limb being worked (eg on the top of the leg or the top of the arm) in order to partially restrict blood flow into that limb.
“This restriction is combined with low-load resistance exercise or low-intensity aerobic exercise (opens in new tab) in order to produce benefits similar to that of high load or higher intensity exercise.”
As an example, BFR can be used when doing bicep curls. When performing this exercise, you would place and tighten a cuff around the proximal part of the arm (nearest the body) to limit blood flow to the working muscle (the bicep). Through this, Loenneke says, you can lift lighter weights while experiencing the same hypertrophy (opens in new tab) and strength benefits of training with heavier loads.
How blood flow restriction training works
How blood flow restriction increases muscle size is not entirely known, says Loenneke, but is likely to be similar to that of traditional resistance exercise.
“In other words, when a muscle contracts, that contraction initiates a signal which turns on the growth promoting pathways (e.g. mTORC1) in the activated muscle fibers. As exercise becomes more difficult, more fibers are activated.
“The application of blood flow restriction makes the muscle work harder than it normally would, leading to higher levels of muscle activation. This means that more and more fibers are signaled to grow, even though the load being lifted is very light (20-30% of maximum strength).”
What equipment is needed?
A cuff or wrap is needed to perform blood flow restriction training. And, with the popularity of the practice mounting, many of these products are available commercially – in stores and online. These cuffs are available in two main styles: inflatable, like the B Strong cuffs (opens in new tab) below and practical.
“There are a number of commercial options available for those interested in applying blood flow restriction,” says Loenneke. “The main components include the cuff and a device for inflating the cuff.
“Many of the commercial devices available today also allow for the setting of a personalized limb pressure – that is, a pressure that accounts for the cuff used and the size of the limb to which that cuff is being applied (eg apply cuff to 40% of the pressure needed to completely cut off blood flow).
“Another method is to apply practical blood flow restriction through an elastic wrap or cuff. This method is called ‘practical’ because elastic wraps are easy to find and are inexpensive. The downside of this method is that it does not have a device for regulating pressure, therefore it is not possible to know how much restriction is being applied.”
What are the benefits
At first glance, the benefits of blood flow restriction might seem too good to be true: namely, promoting hypertrophy and strength gains while lifting lighter weights, thus lowering the risk of injury for exercisers and allowing deconditioned individuals to train with greater efficiency. However, there is literature to support these claims.
“The majority of the work [studying BFR] has focused on changes in muscle size and strength,” says Loenneke. “Blood flow restriction in combination with low load resistance training increases muscle size and strength.
“The change in muscle size is similar to that of high load (70% of the most weight an individual can lift) exercise. However, the change in maximal strength is often less – strength still increases, just not to the same extent.”
A 2010 study published in the Clinical Physiology and Functional Imaging journal tasked 10 young men with completing four sets of bench press totalling 75 repetitions at 30% of the heaviest weight they could lift for a single repetition. They did this twice daily, six days a week, for two weeks, with one group using elastic cuffs placed proximally on both arms for BFR and the remaining subjects performing the exercise without cuffs.
After two weeks the BFR group saw a 6% increase in their maximum bench press, an 8% increase in the muscle thickness of their triceps and a 16% increase in the muscle thickness of their pectoralis major (the largest of the chest muscles).
In contrast, the control group’s bench press one rep max fell by 2%, and the muscle thickness of their triceps and pectoralis major barely changed (-1% and 2% respectively).
This may partly be down to BFR’s ability to impact the endocrine system. A 2016 study published in the European Journal of Applied Physiology (opens in new tab) found that four weeks of low-intensity resistance training with blood flow restriction led to a significant increase in growth hormone levels.
The ability to reap similar rewards from resistance training and other forms of exercise, while using lower loads and placing less stress on the body as a result, could be beneficial to individuals or groups who are unable to participate in more intense activities, Loenneke says.
“There are certain populations that might be able to improve muscle size and strength through slow walking or cycling with blood flow restriction, but the largest changes occur when blood flow restriction is combined with resistance type exercise.
“Some work suggests that the application of blood flow restriction by itself might be able to slow down the loss of muscle size and strength with bed rest. The data for that, however, is quite limited.”
Who should do it
It may not be a mainstream practice among regular exercisers, but Loenneke says blood flow restriction is something that can be used by everyday gym-goers looking to increase their strength and muscle mass. However, he advises incorporating it into your training routine, rather than tacking it on to the end of an already full workout schedule.
“[Gym-goers] could use it as part of their normal training program or they might choose to implement it when they are injured or seeking to add some variety to their training,” says Loenneke. “Some like to incorporate it towards the end of the workout after they’ve done some of their more traditional training.
“This can be effective, but it is important to realize that a muscle can only respond so much to a given training session. If you’ve already done multiple sets of multiple exercises for a particular muscle group, it is unlikely that adding another exercise with blood flow restriction will add anything extra.”
Is blood flow restriction training dangerous?
While all exercise has associated risks, many fears regarding BFR are unfounded, says Loenneke. However, more research is needed.
“Two common concerns are the risk for muscle damage and blood clots. The available literature suggests that adding blood flow restriction to exercise does not appear to increase the risk for either. This, of course, assumes that the stimulus is used appropriately .”
Existing literature supports this. A 2021 systematic review of studies into the subject, published in the International Journal of Sports Physical Therapy (opens in new tab), states: “It appears the greatest advantage of BFR is its ability to safely augment exercise intensity in healthy and comorbid individuals. However, more research is needed before fully determining the long-term systemic effects of BFR.”