Using blood flow restriction to improve hypertrophy has been a hot topic lately. The basic idea behind blood flow restriction, or occlusion, is that you can build muscle better by using a tourniquet of some kind on your legs or arms. It sounds a little weird, no doubt, but it is receiving increasing acceptance and interest in the scientific community.


However, the question of why occlusion works remains unclear. Researchers published a study this month in the Journal of Strength and Conditioning Research to address that question. The study focuses on practical blood flow restriction, a method of occlusion that employs common and inexpensive means of restricting blood flow, such as knee and hand wraps. This method of occlusion has replaced the use of blood pressure cuffs and other expensive devices that were common in the original studies.  


The key to effective blood flow restriction is occluding only the veins and not the arteries. Veins are closer to the surface of your skin, which is why you can see them. They are also not pressurized in the way that arteries are. Because of this, your veins take less pressure to block than your arteries do, making venous occlusion possible without arterial occlusion. You just don’t tie the wrap as tightly.


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Amazingly, occlusion seems to allow you to lift lighter weights, say 30% of your max, and get the same results as you would at a heavier weight without restricting your blood flow. The idea that you could use lighter weights than normal but still get the same results opens up the possibility for more training. You would get the same results, but perhaps with less muscle damage.


There are numerous mechanisms that may cause superior muscle building with blood flow restriction. In this study, the researchers focused on three indicators of hypertrophy: muscle activation, muscle swelling, and muscle damage. They examined the acute effects of occlusion on these three mechanisms. In other words, they wanted to know what happening during and immediately after a workout.


The researchers discovered that the muscles received greater activation and were thicker by using blood flow restriction at 30% of max effort. The idea is that both of these effects will yield greater muscle size in the long run. The researchers also found the same levels of lactate, soreness, power performance, and swelling with blood flow restriction as they did without. So, in theory, occlusion is better for muscle size but doesn’t cause any more damage.


However, there were some oddities to this study. For some reason, the researchers noted that post-workout muscle thickness was a good thing, but muscle swelling was bad. And yet, as far as I can tell, there was no distinction between the two other than what they were called in the study. Although there was indeed more swelling immediately after the occlusion training, it had normalized by the following day. The change in acute muscle thickness is sort of a weird mechanism to study, anyway. Hormonal changes may have been more informative. Nevertheless, despite some minor strangeness, this study is just further evidence that blood flow restriction is an effective way of increasing muscular size. 



1. Jacob Wilson, et. al., “Practical Blood Flow Restriction Training Increases Acute Determinants of Hypertrophy Without Increasing Indices of Muscle Damage,Journal of Strength and Conditioning Research, 27(11), 2013


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