Blood-flow restricted training 101

Jeremy Loenneke is an assistant professor of Exercise Science in the Department of Health, Exercise Science and Recreation Management at the University of Mississippi and has a PhD in Exercise Physiology from the University of Oklahoma. He is based in Oxford, Mississippi.

Blood-flow restricted (BFR) training is exactly what it sounds like. It involves restricting blood flow into the muscle you are training, and occluding – or preventing – blood flow out of the muscle. In lab settings this is typically applied with specialised equipment, but can also be applied with knee wraps in the gym.

This type of resistance training allows a person to exercise at low loads – around 20-30% of their maximum – and results in muscle growth similar to that observed with higher loads of around 70% of their maximum. The benefits of BFR have been observed with a variety of exercises, both compound and single-joint movements. Additionally, some evidence suggests that muscles not directly under BFR, such as the chest, may also be improved.

Most of the research is done with a leg extension and arm curl model but some studies have also found improvements in bench press and squat following this type of exercise.

It is important to remember that moderate blood flow restriction – around 40-50% of what it takes to cut off blood flow completely – appears to be just as effective as very high pressures. We caught up with Dr Jeremy Loenneke, one of the world’s leading authorities on BFR, to see how his research is evolving.

What’s your latest research on?
We are continuing to do a lot of methodological work on how to best apply this stimulus. It is pretty well established that low loads with blood-flow restriction increase muscle mass similar to that of high load training. Thus, we are now more interested in making the stimulus more effective and/or safer. Our recent work investigates how different pressures, exercise intensities (percentage of one-rep maximum), cuff sizes, and so on, can affect the acute and/or chronic effects of this stimulus.

Have there been any breakthroughs on using higher pressure restriction?
I think it would be quite premature to say that there are no uses for high pressures, because this would assume that we have compared every variable across low and high pressures. We and others have shown that lower pressure may be all that is required to maximise changes in muscle mass and strength. We base that on some acute and chronic data from our laboratory that suggests that there just doesn’t seem to be any difference between low and high relative pressures. This suggests that, for muscle growth, venous occlusion and subsequent pooling, low to moderate pressure may be all that’s required for this adaptation, therefore there may be little need to increase pressures high enough to affect the arteries.

How are you testing high versus low pressure BFR?
We put the cuff we use during exercise at the top of the arm and we inflate it until we don’t hear a pulse with a Doppler probe at the wrist. This is called arterial occlusion and is the the lowest pressure applied in which there is no blood flow. Whatever that arterial occlusion pressure is, we take a percentage of it and apply that pressure to the individual during exercise. For example, in our recent study we compared 40% (low) to 90% (high) arterial occlusion. Thus, if a person had an arterial occlusion pressure of 100 mmHg, we would apply 90mmHg to one arm and 40mmHg to the other arm.

Does high pressure work better for some people, and low pressure work best for others?
It’s an interesting question and to be honest, I don’t know. I think it might be more situation specific than individual specific. Although I don’t think this is the case, it is possible that there may be certain situations where perhaps higher pressure may work better.

What’s the best methodology at present to apply pressure?
When using pressure controlled devices, cuff width, limb circumference, and brachial systolic blood pressure, are three prominent predictors of arterial occlusion. However, if you are doing the practical model of BFR in the gym, my old recommendations still probably hold true. I would use the workload as a gauge of pressure: if you aren’t getting close to the four set rep range target of 30-15-15-15, then the load is too high or the wraps are too tight.

If you are sure the load is around 30% of your one-rep max and you aren’t getting close to those reps, then the wraps are too tight and need to be loosened. For full disclosure I don’t know if 30-15-15-15 is the most ‘optimal’ rep protocol. This is a protocol that I often recommend because it is something that has repeatedly shown to produce muscle growth.

Some have recommended repetitions to failure, however, I think having a goal amount of repetitions to shoot for often allows people to complete more repetitions and volume than they would have if they had no target.

What are the risks of applying too much pressure?
There is some evidence that muscle growth is attenuated to some degree under the application of the cuff. This is something that has been documented by a couple of papers and part of the reason why I recommend a narrower (3cm to 5 cm) cuff versus a wider cuff (greater than 10cm). However, if you look at those studies, they applied the same pressure to everyone, independent of individual characteristics.

Therefore, it could be possible that this slight attenuation of growth may be due to too high of pressure applied, but that is a hypothesis and should be tested. One thing that has been relatively well documented is that with higher pressures applied, the workload at the heart increases significantly and meaningfully, which may be of concern to some populations. In addition, discomfort is also usually higher with greater pressures, particularly during the rest periods when there is no muscle contraction occurring. Given that the data suggests that – at least for hypertrophy – higher pressures aren’t better, it probably makes sense to apply a low-moderate pressure.