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There is compelling evidence for the practical and beneficial use of low-intensity exercise with BFR (LI-BFR) as an effective tool to facilitate hypertrophic and strength gains across populations, including professional athletes (1-4), the elderly (5,6), healthy adults (7) and during musculoskeletal (MSK) rehabilitation (8-13). Remarkable too is the fact that BFR is used almost exclusively in research or clinical settings despite its proven efficacy, though strength and conditioning coaches are beginning to use it successfully with professional athletes during periods of disuse to maintain muscle size and strength, and to accelerate rehabilitation (14). Its impressive ability to stimulate muscular hypertrophy is gaining (small amounts of) attention in the gym market, but a lack of accessible information and current logistical and safety limitations are preventing its widespread use. We have developed the Hytro business specifically to overcome these issues, by providing a safe, effective, and simple way to perform BFR with our patented Performance TechWear.
We also deliver a platform for BFR education and for the progression of scientific research.
BFR involves the application of a tourniquet to the most proximal portion of the arm or leg causing vascular occlusion, but only partial arterial occlusion. Oxygenated blood flows into the limb while return venous flow is restricted, causing cell swelling as blood accumulates in the muscle. By combining BFR with low intensity exercise (LI-BFR), blood flow increases and muscle swelling intensifies causing a cascade of physiological reactions, the sum of which is increased mTOR signalling and protein synthesis in the muscle (15).
It’s widely accepted among researchers that high intensity resistance training (HIRT) – lifting repetitions of a weight approximately 70% 1 repetition max (1RM) – is required to optimise muscular hypertrophy. Remarkably, studies have shown that LI-BFR achieves a similar hypertrophic response to HIRT, using only 20-30% of 1RM! Furthermore, combining HIRT with LI-BFR augments the body’s stimulation of muscle protein synthesis (MPS), improving its ability to hypertrophy beyond HIRT alone. Moreover, as LI-BFR does not appear to cause any significant muscle damage, supplementing normal high load training with this technique may be an effective means to improve muscular adaptations in healthy adults (7,16). This unique training method elicits many impressive physiological responses in the body and its benefits are well documented for increasing muscle mass and strength (3,4,17-20), muscular endurance (21,22), power output (2), and aerobic capacity. More impressively, significant muscular improvements have been illustrated in well-trained athletes, who would not normally benefit from low load exercise (16).
UNDERSTANDING MUSCLE FIBER RECRUITMENT
Recruitment of muscle fibers is controlled by the type of exercise performed. Type I or slow oxidative (SO) fibers are recruited to perform endurance type exercise, requiring a high rate of oxygen delivery from the capillaries to the mitochondria to produce energy. Likewise, type IIA or fast oxidative (FO) fibers require oxygen for energy production and therefore contain many capillaries and mitochondria, but they can also contract anaerobically to some extent. Lastly, larger type IIX or fast glycolytic (FG) fibers produce energy much more rapidly, but in smaller quantities, in a process called anaerobic respiration which does not use oxygen. FG fibers are recruited when performing shorter more explosive movements like sprinting or heavy weightlifting, and contain much smaller concentrations of capillaries and mitochondria.
Now that you understand how muscle fibers are recruited, let’s look at the physiological mechanisms behind BFR.
Under normal conditions, oxygenated blood is transported into the muscle via an artery and associated capillaries, providing the muscle cells with glucose and oxygen to produce energy (ATP) in a process called aerobic respiration. Deoxygenated blood flows back to the lungs to reoxygenate, and back to the heart for redistribution around the body. However, with BFR applied, the limb is partially occluded, restricting the return flow of blood, causing a build-up of deoxygenated blood in the limb.
The ischemic exercise results in cell swelling, and ultimately a condition of hypoxia in the muscle. A hypoxic state induced through BFR means that there’s less oxygen available for SO and FO fibers to extract and produce energy, which rapidly leads to fatigue of these fibers. FG fibers are consequentially recruited to help the muscles contract, despite the body performing low intensity exercise that would not usually stimulate FG fiber contraction. The body forcibly recruits all muscle fibers into action, resulting in increased muscular hypertrophy. Concurrently, lactic acid and other toxic metabolites accumulate in the muscle causing metabolic stress which sets off a cascade of physiological reactions responsible for increased protein synthesis signalling. The brain stimulates a ~9-fold increase in the release of growth hormone (23), while the mammalian target of rapamycin (mTOR) signalling pathway, a central regulator of MPS, increases MPS activity and stimulates muscle hypertrophy (15). These profound effects are not limited to the occluded limb either. As blood flow is restored around the body, other tissues will be affected systemically. As an example, physiotherapists often perform resistance training with a client’s uninjured limb for a crossover effect on the injured limb.
Despite the observed benefits of this unique exercise method, a standardised protocol is yet to be established. For example, a wide range of devices have been used to restrict blood flow, including nylon pneumatic cuffs (24,25), traditional blood pressure cuffs (26,27), elastic belts with a pneumatic bag inside (28,29), and elastic knee wraps (30-33). The use of elastic wraps for BFR was first proposed by Leonneke and Pujol (30) and is often referred to as ‘practical BFR’ because it circumvents the need for expensive equipment, improving accessibility and usability. This method has since been demonstrated to provide a safe, effective and ecologically valid occlusive stimulus for BFR training.
A wide range of restrictive cuff pressures have also been documented in the research, including the use of a standardised limb occlusion pressure (LOP) across participants, pressure relative to the patient’s systolic blood pressure, and pressure relative to the patient’s limb circumference. These methods are however only available to those with suitable equipment which led to the adoption of a more practical means of applying pressure (i.e. wraps) through using a perceived measure of tightness (30-32,34,35). Previous research found that sufficient occlusive pressures can be applied when participants rated the level of tightness from the cuff as a 7 out of 10, indicating that a perceived scale of tightness can be a viable method for determining an appropriate level of cuff restriction (34).
Hytro’s patented Performance TechWear demonstrates the novel incorporation of a BFR cuff with clothing. Both the Velcro and strap components of our mechanism are sleek and discreet, providing the highest level of comfort while working out, unseen in other BFR products. More important still is the specific anatomical positioning of the cuff proximal on the limb, above the bicep insertion and below the gluteal fold for the arm and leg respectively, ensuring safe placement for the user with each and every use, and, without the need for professional help.
Specifically, the mechanism comprises: