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Mechanisms Of Blood Flow Restriction

Blood Flow Restriction, What is it?

Overview of the Mechanisms of BFR

Blood Flow Restriction (BFR) training has been shown by itself or in combination with low intensity exercise to be beneficial for skeletal muscle adaptations.¹ Low load resistance training is usually prescribed in combination of BFR to produce a potent stimulus that has been shown to be beneficial for hypertrophy and strength¹. The benefits for BFR have been shown to elicit performance and rehabilitative gains alike.¹ The literature suggests that training with low load in combination of BFR may promote a superior stimulus than traditional high load resistance training.¹ Ultimately, this sparks the controversy of whether or not individuals could be training with a lower load and achieving greater neuromuscular gains.¹

How it Works?

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.²The external pressure mechanism restricts venous return resulting in a hypoxic environment within the skeletal muscle tissue.^1,2

Metabolic Stress

There appears to be numerous mechanisms that occur Intra-muscularly with occlusion. First, there is metabolite accumulation of lactate creating 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.³

Fiber Recruitment

Fiber type recruitment may also play an important role in hypertrophy during BFR training.³ The size principle states that slow twitch fibers are recruited first with lower intensities while gradually increasing recruitment of fast twitch fibers with an increase of intensity. Researchers have speculated that with a decrease in oxygen availability there is an increase in recruitment of additional motor units to counteract the overall deficit in force development.³ Evidence supports this hypothesis showing increases in motor unit amplitudes and firing rates during occlusion training.³Some evidence also shows no practical difference between intra-muscular electromyography (EMG) between high intensity non-occlusion and low intensity occlusion training.³ Researchers have also identified that low-intensity occlusion results in significantly higher EMG readings than non-occluded training.³ Based on the available evidence, it appears that occlusion training results in higher motor-unit recruitment, which may facilitate muscular hypertrophy in summation of the metabolic response.^2,3

mTOR Pathway

The mTOR signaling pathway has been shown to be a critical player in the regulation of muscular hypertrophy by stimulating muscle protein synthesis.³ Low-Intensity BFR has been shown to stimulate the mTOR signaling pathway, which in turn can facilitate muscular hypertrophy adaptations.³ This implies that the practical application of BFR can be seen from a intracellular signaling response with low-intensity exercise while occluded.

Heat Shock Proteins

Heat shock proteins (HSP) are stress proteins that aid in the translocations of proteins.^2,3 HSPs are activated by physiological stressors such as hypoxic environments, ischemia, and heat. HSPs have been shown to modulate and maintain cellular homeostasis.^2,3The main mechanism or role that HSPs have been theorized is to limit oxidative stress caused by ROS production in the body.³ Researchers have theorized that increasing HSPs levels are associated with increasing levels of muscular hypertrophy and the attenuation of atrophy.³

Conclusion

Based on the research it appears that BFR may be a very useful tool for performance, quality of life, and rehabilitative purposes. This first blog post was a general overview of the possible physiological mechanisms that are associated with muscular adaptations from a BFR stimulus. Although there is a decent amount of literature out there, the mechanisms for resultant muscular adaptations still need further research. Practitioners can assume that muscular adaptations are primarily from mechanical tension and metabolic stress, which in turn facilitate growth through a variety of cellular and metabolic responses.

References

Loenneke, J. P., Wilson, G. J., & Wilson, J. M. (2009). A Mechanistic Approach to Blood Flow Occlusion. International Journal of Sports Medicine, 31(01), 1–4. doi: 10.1055/s-0029-1239499

Loenneke, J. P., Abe, T., Wilson, J. M., Ugrinowitsch, C., & Bemben, M. G. (2012). Blood Flow Restriction: How Does It Work? Frontiers in Physiology, 3. doi: 10.3389/fphys.2012.00392

Pearson, S. J., & Hussain, S. R. (2014). A Review on the Mechanisms of Blood-Flow Restriction Resistance Training-Induced Muscle Hypertrophy. Sports Medicine, 45(2), 187–200. doi: 10.1007/s40279-014-0264-9

Blood Flow Restriction Vs High Intensity Resistance Training

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.¹The external pressure mechanism restricts venous return resulting in a hypoxic environment within the skeletal muscle tissue.¹BFR 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.³The 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.⁶On 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

Loenneke JP, Abe T, Wilson JM, Ugrinowitsch C, Bemben MG. Blood Flow Restriction: How Does It Work? Frontiers in Physiology. 2012;3. doi:10.3389/fphys.2012.00392

Loenneke JP, Wilson GJ, Wilson JM. A Mechanistic Approach to Blood Flow Occlusion. International Journal of Sports Medicine. 2009;31(01):1-4. doi:10.1055/s-0029-1239499.

Pearson SJ, Hussain SR. A Review on the Mechanisms of Blood-Flow Restriction Resistance Training-Induced Muscle Hypertrophy. Sports Medicine. 2014;45(2):187-200. doi:10.1007/s40279-014-0264-9.

Wernbom M, Apro W, Paulsen G, Nilsen TS, Blomstrand E, Raastad T. Acute low-load resistance exercise with and without blood flow restriction increased protein signalling and number of satellite cells in human skeletal muscle. European Journal of Applied Physiology. 2013;113(12):2953-2965. doi:10.1007/s00421-013-2733-5.

Loenneke JP, Wilson JM, Marín PJ, Zourdos MC, Bemben MG. Low intensity blood flow restriction training: a meta-analysis. European Journal of Applied Physiology. 2011;112(5):1849-1859. doi:10.1007/s00421-011-2167-x.

Lixandrão ME, Ugrinowitsch C, Laurentino G, et al. Effects of exercise intensity and occlusion pressure after 12 weeks of resistance training with blood-flow restriction. European Journal of Applied Physiology. 2015;115(12):2471-2480. doi:10.1007/s00421-015-3253-2.

Shephard R. Strength Training with Blood Flow Restriction Diminishes Myostatin Gene Expression. Yearbook of Sports Medicine. 2012;2012:92-93. doi:10.1016/j.yspm.2012.03.023.

Carroll C, Bs TE, Bs GW. Comparisons between Low-Intensity Resistance Training with Moderate Blood Flow Restriction and High-Intensity Resistance Training on Quadriceps Muscle Strength and Mass. Journal of Athletic Enhancement. 2017;06(03). doi:10.4172/2324-9080.1000257.

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.

Takarada Y, Takazawa H, Sato Y, Takebayashi S, Tanaka Y, Ishii N. Effects of resistance exercise combined with moderate vascular occlusion on muscular function in humans. Journal of Applied Physiology. 2000;88(6):2097-2106. doi:10.1152/jappl.2000.88.6.2097.

Blood Flow Restriction in Older Adults

BFR vs Traditional Strength Training in the Elderly

In the literature Blood Flow Restriction (BFR) is predominantly utilized for muscular hypertrophy or to offset atrophy following injury. Although BFR has been shown to elicit similar cellular and muscular adaptations when compared to traditional exercise, performance metrics such as strength and power need to be explored further. If the ability to achieve morphological adaptations from BFR exists, practitioners may speculate that BFR could potentially play an important role in a traditional strength program as well. Currently, for traditional exercise prescription, hypertrophy and strength gains are usually prescribed around 70-100% 1-Rep Maximum (1RM).¹ Although this has been shown through decades of literature, the ability of low-intensity BFR to achieve similar functional muscular performance is of high controversy of late.

Elderly Overview

BFR has been shown to be an appropriate and effective tool in numerous environments. One of the most intriguing populations that may see large benefit of BFR is elderly subjects.¹ As we know, the elderly lose bone mineral density, have an increase of muscular atrophy, and are at risk for falls and mortality surrounding functional and metabolic capacities.^1,2 Therefore, being able to appropriately train to stimulate functional performance and muscular gains in a safe and effective manor are of high importance. In order to offset decrements of skeletal muscle, traditional high-load exercise is usually prescribed. The issue is that with age there is a decrease for mechanical stress and tolerance with higher prevalence of comorbities.² Therefore it would be ideal to prescribe lower-intensity training while still maximizing functional performance, muscular, and skeletal adaptations from exercise in the elderly to improve quality of life and mortality.

Low-Intensity BFR Vs High-Load Hypertrophy & Strength

The evidence shows that both Low-Intensity BFR (20-40% 1-RM) and High-Load (70-90%) elicit similar changes in muscle mass in older adults.² In the systematic review done by Centher et al. the authors concluding that 5 studies comparing Low-Intensity BFR and High-Load traditional have no statistical significant differences in muscular morphological adaptations.² This implies that from a hypertrophic standpoint older adults may benefit from utilizing lower-intensity prescription while delaying atrophy and potentially increasing cross-sectional area of muscle. This is extremely important because skeletal muscle mass may decrease between 3-8% per decade after 30 years of age.² If the elderly population can offset or delay atrophy while implementing lower-intensity exercise, we may see a rise in compliance leading to habitual exercise engagement.²Although no significant differences were found between groups for muscle mass, strength gains showed significant variance.²Between group differences revealed High-Intensity prescription elicited a 24.0% +/- 16.2% in comparison to 14.4 +/- 6.3 in the Low-Intensity group. Practitioners should take into account that although similar muscle mass was seen between protocols, high-load still may be king to elicit strength stimulus in the elderly population.

Low-Intensity BFR Vs Low-Intensity

In order to determine the overall effectiveness of BFR, control and comparisons of Low-Intensity exercise stimulus is needed. In the same review done by Centner et al. the authors compared 9 studies measuring strength between LI-BFR and Low-Intensity exercise. Between all of the LI-BFR training there was an average muscular strength increase of 12.3 ± 4.1%, compared to 2.5 ± 2.7% with Low-Intensity exercise. The authors demonstrated these increases were stastistically significant p < 0.001. This means that between 9 peer-reviewed study, Low-Intensity exercise with BFR was significantly superior than just Low-Intensity exercise alone.

Low-Intensity BFR Vs Walking

BFR has been shown to elicit benefits from normal functional activities such as walking.² This is a very important discovery because low-intensity walking is very common among the older population and a preferred method of exercise that almost anybody can do. A combination of studies have shown that BFR in combination of low-intensity walking is a far superior stimulus than walking without BFR.² In fact walking alone with BFR was shown to increase muscular strength by 13.3%. Although walking alone may be beneficial for muscular mass and an appropriate stimulus, in appears that BFR in conjunction with walking may elicit overall great functional performance gains in the elderly population.²

References

Carroll, C., Bs, T. E., & Bs, G. W. (2017). Comparisons between Low-Intensity Resistance Training with Moderate Blood Flow Restriction and High-Intensity Resistance Training on Quadriceps Muscle Strength and Mass. Journal of Athletic Enhancement, 06(03). doi: 10.4172/2324-9080.1000257

Centner, C., Wiegel, P., Gollhofer, A., & König, D. (2018). Effects of Blood Flow Restriction Training on Muscular Strength and Hypertrophy in Older Individuals: A Systematic Review and Meta-Analysis. Sports Medicine, 49(1), 95–108. doi: 10.1007/s40279-018-0994-1