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.² The 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.³ Some 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.^2,3 The 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