The process of applying thigh and arm tourniquets to impair blood flow while strength training was developed more than 50 years ago in Japan, where it is referred to as KAATSU training (1). Original advocates of this training technique wrapped straps around their thighs and arms with so much pressure that blood flow to the extremity was nearly completely obliterated. The resultant hypoxic environment induced muscle damage resulting in large releases of growth hormone, which in turn produced significant increases in muscle hypertrophy. Several studies have shown that blood flow restriction training (BFR) produces muscle hypertrophy in less than 3 weeks, with 290-fold increases in growth hormone production (2). Although effective, the high cuff pressures used to impair circulation tend to be uncomfortable, and the popularity of blood flow restriction training has been mostly limited to diehard strength enthusiasts.

Recently, several studies have shown that it is not necessary to produce full occlusion of blood flow in order to get all of the benefits associated with blood flow restriction training (3,4) (Fig. 1). The ability to build muscle mass using light resistance is clinically important, as it allows athletes to begin strength rehabilitation within days of an injury, not weeks. BFR also allows older individuals to maintain muscle mass without the risk of being injured by lifting heavy weights. One review of the literature found that people over 60 were 10 times more likely to be injured while exercising than their younger peers (5).

To evaluate the efficacy of blood flow restriction training using less forceful compression, researchers from Brazil assigned 30 young males to 1 of 3 exercise protocols (6). The first group was asked to do 4 sets of 10 repetitions using heavy weights. The second group was asked to perform moderate to high intensity endurance training by cycling at 70% full effort for 30 minutes. The last group was told to ride a bicycle for 30 minutes at about 40% full effort while wearing a blood flow restriction strap. The strap was wrapped around the upper thigh with a comfortable force that was the equivalent of a blood pressure cuff being inflated to 95 mmHg; i.e., the equivalent of a firm handshake. All of the subjects performed their specific exercises 4 times per week.

At the end of the 8-week training session, researchers were surprised to see that the subjects who wore compressive straps while riding a bicycle at a comfortable pace had measurable increases in muscle mass, while also showing substantial improvement in aerobic fitness despite the light effort. The blood flow restriction group increased muscle mass nearly 11%, while the subjects in the heavy resistance group increased muscle 12.5% (hardly worth the added effort). Moreover, the subjects in the light exercise group also improved aerobic capacity by 11%, which is a considerable improvement given the reduced total workload associated with exercising at such a low intensity. The authors relate the improved aerobic capacity to the fact that blood flow restriction straps increase the release of vascular endothelial growth factors, which promote the formation of capillaries thereby improving aerobic fitness.

The findings of this paper are important as they shed new insight into the molecular mechanisms associated with blood flow restriction training. This research proves it is possible to increase both muscle mass and aerobic fitness while exercising for brief periods of time at a comfortable pace. A similar study from Japan found that wearing compressive straps around the thighs while walking produced substantial increases in quad muscle volume in just 10 weeks (7).

Since the latest research shows vigorous compression of a muscle is not necessary to get excellent results, and because high pressure may increase the risk of dangerous blood clots (especially in postsurgical patients), it is important to compress the muscle with the least pressure capable of producing positive results. Although large- scale studies have shown that even forceful muscle compression while exercising is safe for the general population, it makes sense that if you can get the same increases in strength and aerobic capacity with light pressure, then only light pressure should be utilized. Pressures as low as 50 mmHg on a blood pressure cuff have been shown to promote muscle remodeling as effectively as high-pressure cuffs (4).

Because you can build muscle with even light resistance, BFR is perfect for people with knee arthritis, as they can significantly increase muscle mass while lifting light weights through a smaller range of motion (8). BFR training is also great for managing muscle strains. Laboratory studies show that even badly strained muscles can be exercised with light resistance without worsening the muscle tear (9). In my experience, recovery rates for adductor and hamstring injuries can be cut in half by using BFR training.

Whether your goal is to accelerate recovery or increase muscle mass and aerobic capacity, BFR can be a great addition to your rehab routines. As mentioned, even though wearing compressive straps while exercising has been proven to be safe and effective for almost everyone, people who have recently had surgery, especially joint replacements, should wait at least three months prior to initiating BFR. This is also true for people with a history of clotting disorders and/or people with symptoms such as unexplained swelling, pain, soreness and/or discolored skin. In their 2019 paper evaluating the risk/rewards associated with blood flow restriction training, Bond et al. (10) claim that while the collective literature indicates that blood flow restriction training poses little risk of directly causing injury (even at high strap pressures), the ideal candidate for this type of training is an active person who exercises regularly, but has difficulty with high intensity workouts. This is especially true for people over 60, who would like to avoid the proven risks associated with heavy resistance exercises (5), and for injured athletes, who want to achieve optimal performance as quickly as possible.

References:

1. Sato Y. The history and future of KAATSU training. Int J Kaatsu Train Res. 2005; 1: 1–5.
2. Takarada Y, Nakamura Y, Aruga S, et al. Rapid increase in plasma growth hormone after low-intensity resistance exercise with vascular occlusion. J Appl Physiol. 88: 61–65,2000
3. Sieljacks P, Degn R, Hollaender K, et al. Non-failure blood flow restricted exercise induces similar muscle adaptations and less discomfort than failure protocols. Scand J Med Sci Sports. 2018;1-12.
4. Daeyeol D, Loenneke J, Ye X. Low-load resistance training with low relative pressure produces muscular changes similar to high-load resistance training. Muscle Nerve 56: E126–E133, 2017
5. Kallinen M. Cardiovascular benefits and potential hazards of physical exercise in elderly people. J Sports Sci Med. 2005; 4, Suppl.7,1 – 51.
6. Conceicao M, Junior E, Telles G, et al. Augmented anabolic responses after 8-week cycling with blood flow restriction. Med Sci Sports Exerc. 2019;51:84–93.
7. Ozaki H, Kakigi R, Kobayashi H, et al. Effects of walking combined with restricted leg blood flow on mTOR and MAPK signaling in young men. Acta Physiol (Oxf). 2014;211:97–106.
8. Ferraz R, Gualano B, Rodrigues R, et al. Benefits of resistance training with blood flow restriction in knee arthritis. Med Sci Sports Exerc. 2018;50: 897-905.
9. Hasselman C, Best T, Seaber A, et al. A threshold and continuum of injury during active stretch of rabbit skeletal muscle. Am J Sports Med. 1995;23:65-73.
10. Bond C, Hackney K, Brown S, et al. Blood flow restriction resistance exercise as a rehabilitation modality following orthopedic surgery: a review of venous thromboembolism risk. J Orthop Sports Phys Ther. 2019; 49:17-27.