Blood Flow Restriction (BFR) training has growing in popularity in a variety of sports performance environments. The BFR technique is characterized by using a pneumatic tourniquet system that applies an external pressure to the proximal regions of an upper or lower limb.1 The external pressure mechanism restricts venous return resulting in a hypoxic environment within the skeletal muscle tissue.1 BFR is generally utilized in a combination of lower-intensity loads (20-40%) in combination with traditional resistance training. Currently for traditional exercise prescription, hypertrophy and strength gains are usually prescribed around 70-100% 1-Rep Maximum (1RM).2 Although the benefits of resistance training has been shown through decades of literature, the ability of utilizing BFR in combination with low-intensity exercise to achieve similar functional muscular performance is of high controversy of late. If the ability to achieve superior or matching morphological and neurological adaptations from BFR exists, practitioners may speculate that BFR could potentially play an important role in combination of a traditional strength program.
Purpose
Therefore, the purpose of this paper is to compare and contrast the controversy of BFR and high-intensity resistance training on skeletal muscle hypertrophy and muscular strength.
Mechanisms of BFR
BFR or occlusion of the muscle has been shown to induce a unique metabolic and mechanical stimulus that appears to drive adaptation.3 The mechanisms for adaptation are still being researched, but there appears to be a growing body of evidence to support the current theories. From a metabolic perspective one of the primary mechanisms is an accumulation of lactate, which creates an overall lower pH environment.3 From a lower pH level, there is a cascade effect of stimulating the anabolic growth hormone (GH). Although acute levels of GH may not be necessary for muscular hypertrophy, researchers have speculated that an accumulation of GH over time may lead to long-term muscular adaptations. Some of the speculated theories for secondary mechanisms associated with metabolic stress and hypertrophy are: increasing of motor unit recruitment, systemic hormone production, cell swelling, increased reactive oxygen species, muscular damage, and muscle protein signaling and cellular responses.3,4
Muscle Strength
Traditional strength training prescription for muscular strength adaptations generally is prescribed between 70-90% 1-Repetition Maximum (1RM). Strength adaptations are usually characterized with high load resistance training rather than low load.5 The ability of BFR to potentially induce neuromuscular strength adaptations in combination of low intensity exercise may allow for a reduction in overall mechanical stress and unwanted by products of high intensity resistance training.5 Ultimately if BFR training is able to induce a similar or superior strength adaptations in comparison to high load training, there could be a time and place to utilize the this methodology within the sports performance field.5 In one study comparing the effects of 8 weeks of High-Intensity (HI), Low-Intensity (LI), and Low-Intensity with BFR (LIR), gains of (40.1%, 20.7%, and 36.2%) were found respectively.6 All groups significantly increased from pre-posttest, with no statistical significance between LIR and HI protocols.6 On the other side of the argument a in 12 week study done comparing LI BFR (20-40% 1RM) with traditional HI resistance training (80%) researchers found that BFR protocols increased muscle strength by (~12.10%) in comparison to HI training (21.60%).7 To further the comparison another study done in older adults comparing LI BFR training with HI training identified (~54%, and 17%) gains in 1RM from HI and LI BFR training respectively.8 In contrast, a study done by Karabulut et al.9 found similar increases between LI BFR (20% 1RM) and HI resistance training (80%) showing an overall increase of (19.3% and 20.4%) in leg press strength in LI BFR and HI training respectively.9 Interestingly the same study identified statistical greater significance in leg extension strength (19.1 and 31.2%) increases from baseline between LI BFR and HI training respectively.
It appears that LI BFR can induce superior strength gains when comparing with LI alone. Although research is conflicting between LI BFR and HI resistance training, the evidence is points towards HI resistance training as a superior stimulus for muscular strength adaptations.10 It should be noted that a few studies showed similar increases in strength gains when comparing in older adult populations.7,8 Therefore the context of age, activity level, and overall fitness could dictate when or when not LI BFR training to be more optimal stimulus.
Muscular Hypertrophy
BFR training has been thought to be a very beneficial methodology for inducing muscular hypertrophy.10 As of late BFR has been highly campaigned as being superior or matching stimulus for muscle mass gains in comparison to traditional HI resistance training.10 LAURENTINO et al. study6 showed significant increases in pre-posttest muscle cross sectional area gains (6.3% & 6.1%) in LI BFR and HI training respectively. To further the evidence, Lixandrão et al. study7 researchers found no statistical significance in cross sectional muscle gains (5.3%, and 5.9%) between HI resistance training and LI BFR respectively. Another study11 found statistical increases in muscle cross-sectional area from 16-weeks of elbow flexor training with LI BFR training and HI resistance training (20.3% and 17.8%) respectively.
Based on the evidence it appears that both LI BFR and HI training induce a similar muscular hypertrophy adaptation result. From the previous discussed literature both LI BFR and HI training induced greater muscular gains in comparison to LI training alone. Although there is much controversy regarding the methodology involved with BFR training, it appears that HI training and LI BFR may both produce similar muscular adaptation. It’s important to note that there has been much discussion surrounded around the BFR technique including: cuff width, pressure, and prescription protocol. Although these are all valid questions one meta-analysis found similar muscle adaptation between protocols when accounting for the moderators of prescription, cuff width, occlusion pressure, and the prescription method.10
Discussion
Based on the peer-reviewed literature cited in this paper we can come to a conclusions and speculations regarding BFR training. The data suggests that LI BFR training may be inferior as a potent stimulus for muscle strength adaptation in comparison to traditional HI resistance training. It is important to note that a few of the cited articles found that LI BFR training to be a superior stimulus when comparing with LI resistance training. For muscular hypertrophy adaptation the evidence points towards minimal or negligible statistically significant difference between HI resistance training and LI BFR. This is important as some specific population such as older adults, individuals coming back from injury, and others may benefit from LI BFR with an overall decrease in mechanical stress and tissue tolerance while still being able to achieve significant strength and hypertrophy adaptations.
Stance
My overall stance is that BFR training is a unique and evidence based tool that can play a variety of roles in the sports performance field. Based upon investigation I believe that BFR training can be utilized primarily as a potent stimulus for muscular adaptation at a lower intensity load than normal resistance training to induce significant adaptations. Along with this of course comes with a lot of uncertainty with variability of cuff pressure, width, brands, prescription. It is my opinion that BFR training especially can play an important role in the return to play process of sports performance as atrophy is one of the most common negative effects of injury. If BFR training can induce a hypertrophic environment with a reduction in mechanical tension, maybe we can attenuate muscular atrophy and reduce return to play times. Also from an elderly population perspective having an instrument that can induce muscular hypertrophy with low intensity loads is very practical for the aging adult. Since muscle wasting increase 3-8% per decade after 30 years of age, BFR may be utilized to offset these numbers. The utilization of BFR may also be very beneficial for individuals who have different comorbidities or ailments that restrict them from being able to have high mechanical loading.
Conclusion
BFR is an evidence based tool that has been shown to induce significant strength and muscular adaptations in numerous studies. The ability of BFR to positively affect strength and muscle adaptation may be of high interest especially in individuals who are limited in their ability to exercise with high intensity training loads.
References
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Karabulut M, Abe T, Sato Y, Bemben MG. The effects of low-intensity resistance training with vascular restriction on leg muscle strength in older men. European Journal of Applied Physiology. 2009;108(1):147-155. doi:10.1007/s00421-009-1204-5.
Lixandrão ME, Ugrinowitsch C, Berton R, et al. Magnitude of Muscle Strength and Mass Adaptations Between High-Load Resistance Training Versus Low-Load Resistance Training Associated with Blood-Flow Restriction: A Systematic Review and Meta-Analysis. Sports Medicine. 2017;48(2):361-378. doi:10.1007/s40279-017-0795-y.
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Applied Human & Sport Performance 