Bodybuilders are always looking for tips, strategies, and techniques to make their training more efficient. We all want more strength and muscle hypertrophy for the time we spend training, right? Consistency is important, but so is varying the way you strength train periodically. One technique that researchers have looked at is called blood flow restricted training. It’s a very popular way of training in Japan where it is sometimes referred to as katsu. What is blood flow restricted training, and does it really boost muscle hypertrophy?
What is Blood Flow Restricted Training?
Blood flow restricted training is a training approach where you attach a wrap to the limb you’ll be training. The purpose of the wrap is to restrict blood flow. The wrap is placed loosely enough to allow blood to flow into the artery but tight enough to prevent the blood from leaving the muscle through the vein. Arteries are blood vessels that carry blood to the muscles and veins carry blood from the muscles back to the heart. This technique allows blood to pool within the muscle you’re working.
What are the benefits of restricting blood flow? For one, you get more of a muscle “pump.” The trapped blood causes the muscle to expand in size and the muscle looks more muscular and well defined, at least temporarily. But the effects aren’t just temporary. It appears to have longer-term benefits for muscle hypertrophy.
Benefits from Lighter Weights
According to research published in Strength and Conditioning Research, blood flow restricted training is more beneficial for building strength and muscle than conventional training when you’re working with light weights. In fact, a study found that training with 20 to 30% of one-rep max increases strength more with blood flow restriction than using the same resistance with conventional training. In other words, blood flow restricted training gives you an advantage if you’re lifting light. But there’s a caveat. When you increase the resistance and lift heavier weights without blood flow restriction, the heavier weights still promote more muscle growth than lifting lighter weights, even with blood flow restriction.
The advantage of blood flow restriction is it lets you build muscle using lighter weights, less than 50% of your one-rep max. How does it work? When you train with lighter loads you don’t recruit as many fast-twitch muscle fibers, but when you add blood flow restriction, the fast-twitch fibers are activated even with lighter loads. The restriction in blood flow fatigues the slow-twitch fibers very quickly and the fast-twitch fibers are forced to chip in. 20 to 30% of one-rep max is far lower than what is considered ideal for muscle hypertrophy, but blood flow restriction changes that.
How Does Blood Flow Restriction Boost Muscle Hypertrophy?
Another advantage of blood flow restriction is it creates metabolic stress, a factor that stimulates muscle growth. There are various ways metabolic stress boosts muscle hypertrophy. For one, metabolic stress elicits the release of growth-promoting chemicals called myokines that favor muscle hypertrophy. Restriction of blood flow also increases muscle fiber recruitment, especially fast-twitch muscle fibers. Remember, slow-twitch muscle fibers thrive on oxygen and blood flow restricted training deprives muscle of oxygen. So, the fast-twitch muscle fibers are forced into action.
But there are other ways in which metabolic stress boosts muscle growth. According to an article by Brad Schoenfeld, Ph.D., C.S.C.S., metabolic stress creates reactive oxygen species that facilitate muscle hypertrophy. Yet another mechanism by which metabolic stress potentially promotes muscle growth is by increasing cellular swelling. Research shows that when muscle cells swell with water, it soups up the rate of muscle protein synthesis and decreases muscle breakdown. Why do muscle cells swell in response to metabolic stress? When a cell is stressed metabolically, lactate builds up, and lactate attracts water into the cell. In turn, this signals anabolic pathways to ramp up muscle protein synthesis. In addition, a study found that even one session of training with blood flow restriction caused a substantial increase in serum growth hormone and that bodes favorably for gains muscle size.
Let’s summarize. Restricting blood flow out of a muscle by using a wrap increases metabolic stress and turns on anabolic pathways that activate muscle growth. It also creates a short-term increase in muscle size. This is referred to as a muscle pump and it’s something bodybuilders are always striving to achieve.
Should You Try Blood Flow Restricted Training?
Training in this manner is a different approach to building muscle size. However, it doesn’t replace conventional training. If you use it, make it a supplement to the training you’re currently doing. Remember, your muscles respond best to workouts that challenge them in different ways. If you’ve reached a plateau, using this type of training may help you jump start muscle growth.
However, there’s no evidence that blood flow restricted training has advantages over conventional high-resistance training. It’s just that you can get similar benefits to high resistance training using lighter weights with blood flow restriction. If you try this method, use lighter weights, no more than 40% of your one-rep max. Studies show lifting at as little as 20% of one-rep max with blood flow restriction is enough to get the benefits.
The Bottom Line
Blood flow restricted training allows you to get some of the benefits of lifting heavy while using lighter weights, as little as 20% of your one- rep max. Don’t use it as your only mode of training but as a supplementary approach to a more advanced training technique. For example, you can use it at the end of a conventional workout. You can also add a few extra sets at the end using lighter weights and blood flow restriction. It’s a different way to train and one that has benefits, especially if you enjoy using lighter weights or need a break from lifting heavy.
StrengthandConditioningResearch.com. “Blood flow restriction training”
LookGreatNaked.com. “The Role of Metabolic Stress in Muscle Growth”
J Appl Physiol 100: 1460–1466, 2006.
J Appl Physiol 88: 61–65, 2000.
Integrative Medicine Research. Volume 3, Issue 4, December 2014, Pages 172-179.