Blood flow restriction (BFR) training involves partially occluding blood flow to a muscle during resistance or cardiovascular exercise using a pneumatic tourniquet (What is blood flow restriction training?). This form of training is generally viewed as an effective alternative for traditional weight training due to the proven benefits for muscular hypertrophy and cardiovascular fitness using relatively low intensity training. There is a growing body of evidence supporting BFR training as a safe and effective training method, when used appropriately. However, the safety and practicality of BFR training has not been extensively studied. While only one large-scale epidemiological study has explored the potential health implications of BFR training (Nakijima, 2006), there remains several proposed risks that should be addressed.
Figure 1: BFR training involves the partial occlusion of blood flow to the exercising muscle.
What are the risks of BFR?The primary concerns surrounding BFR centre on four key areas; increasing muscle damage, blood clotting, augmenting blood pressure and pain/discomfort.
BFR and muscle damage:The research surrounding BFR training and muscle damage is highly varied. It appears that BFR training has the capacity to cause significant muscle damage, and in severe conditions, rhabdomyolysis (Wernbohm et al 2020). The extent of muscle damage appears to be dependent on the training protocol used, specifically the extent and duration of the occlusion stimulus. Muscle damage is a normal response to an unaccustomed training stimulus/exercise, and there is little evidence to suggest adding BFR to exercise adds to the risk. To prevent excessive muscle damage, start with a low level occlusion pressure (discussed below), and gradually progress how long you wear the cuffs during your session.
BFR and blood clotting:Research from surgical tourniquet tells us that complete vascular occlusion can cause the formation of a thrombus (blood clot). The incidence rate of suffering a venous thrombosis during BFR training is 0.06%, and this number is lower than the general population figure. The appropriate use of BFR during exercise does not lead to complete occlusion of blood flow. The timeframe for occlusion is relatively low (5-10mins) and the active muscle contraction pumps blood through the exercising limb. Using excessively high pressure during your training, or using the cuffs for an extended period of time may increase your risk.
BFR and blood pressure:BFR training can augment the cardiovascular response to exercise when compared to an exercise matched control. However, the changes in heart rate and blood pressure observed with BFR training are relatively comparable to what is observed with traditional resistance exercise. While relatively understudied, it is hypothesized that these changes are driven by a decreased venous return and stroke volume, and by an accumulation of metabolites triggering a muscle chemoreflex response. Alternatively there is also strong research that suggests that BFR training facilitates improvements in vascular function. Ten weeks of walk training with BFR increased arterial compliance in a group of 23 elderly subjects (Ozaki et al 2011). Similarly six weeks of walk training with BFR increased venous compliance in 16 elderly females, including subjects considered to be hypertensive (Iida et al 2011).
BFR and pain/discomfort:Once again, the research surrounding BFR training and pain or ratings of perceived exertion, is somewhat conflicting. Some of the more common perceptual responses include fainting/dizziness and numbness. Fainting/dizziness is likely caused by post-exercise hypotension or a vasovagal response. Numbness is likely driven by compression of the peripheral nerve and is often influenced by cuff pressure and the use of a narrow cuff applying direct pressure to the nerve. Both responses have a relatively low incidence rate (0-2%), coincident with traditional resistance, or cardiovascular training. Further, there is no evidence of any long term nerve damage or health implications and these sensations should subside when the cuff pressure is released.
Who is at risk?While there is a growing body of evidence supporting BFR as a safe method of training, it remains relatively understudied. Care should be taken when monitoring individuals considered to be at an increased risk of an adverse reaction to a BFR training protocol. A recent study from Kacin et al (2015) developed a comprehensive screening protocol that is widely considered best practice in assessing suitability for BFR training. Those who appear to be at risk include:
- People with an increased risk of cardiovascular complications should be closely monitored for changes in heart rate and blood pressure. Exercise should be performed with more frequent reperfusions and rest periods. Individuals with a family or personal history of clotting disorders, or level 1 hypertension, may not be safe to complete a BFR training protocol.
- People at a high risk of nerve injury such as diabetics should be constantly assessed for any changes in limb sensation and should consider more comprehensive monitoring of blood glucose.
- Those at an increased of rhabdomyolysis or muscle damage should be monitored for excessive pain or muscle weakness and should consider a passive acclimatization process prior to combining BFR with resistance or cardiovascular exercise.
Figure 2: SujiBFR can measure your individual occlusion pressure ensuring you can train safely and effectively.
How can I use BFR safely?There is currently sufficient evidence that, if used appropriately, BFR training can be administered safely and effectively in a wide range of populations. So, what can you do to keep yourself safe during BFR training?
- Use a personalized limb occlusion pressure (LOP). The amount of pressure required to occlude blood flow is highly individual and driven by various intrinsic (limb circumference, muscle mass, blood pressure) and extrinsic (cuff width, cuff shape, cuff material) factors. Several products exist on the market that have the capacity to accurately measure how much pressure is required to occlude blood flow, giving you piece of mind that your pressure is both safe and effective (Figure 2).
- Progress your training gradually. Like any new health and fitness training routine, your body may take some time to adapt. BFR training is a unique stress on your body. Start at a lower pressure (30-50% LOP) and progress as you get more confident. Once you've achieved your target pressure, you can begin challenging yourself with increasing exercise intensities as able.
- Listen to your body. BFR training, as with any other form of exercise, contains some element of risk and health complications. Specifically, muscle soreness, numbness, fainting/dizziness and bruising are among some of the more common symptoms that you may experience. While there is very little evidence of any long term health implications and these symptoms will likely subside once the pressure cuff is released, if you experience any of these symptoms, you should cease the exercise protocol and consult your healthcare professional.
The Final Word:There is now sufficient evidence that, if used appropriately, BFR training is a safe and effective form of training. As with all forms of training, there is an inherent risk associated and BFR is not immune to this, however adding BFR to exercise does not seem to add to the risk.
- Nakijima, T., et al., Use and safety of KAATSU training: Results of a national survey. International Journal of KAATSU training research, 2006. 2: 5-13. https://www.researchgate.net/publication/324094275
- Wernbohm, M., et al., Commentary: Can Blood Flow Restricted Exercise Cause Muscle Damage? Commentary on Blood Flow Restriction Exercise: Considerations of Methodology, Application and Safety. Frontiers in Physiology. 11(243): 1-7. https://www.frontiersin.org/articles/10.3389/fphys.2020.00243/full
- Ozaki, H., et al., Effects of 10 Weeks Walk Training With Leg Blood Flow Reduction on Carotid Artery Compliance and Muscle Size in Elderly Adults. Angiology, 2011. 62(1): 81-85. https://pubmed.ncbi.nlm.nih.gov/20682613/
- Iida, H., et al., Effects of walking with blood flow restriction on limb venous compliance in elderly subjects. Clinical Physiology and Functional Imaging, 2011. 31: 472-476. https://www.researchgate.net/publication/51701072
- Kacin, A., et al., Safety considerations with blood flow restricted exercise. Annales Kinesiologiae, 2015. 6(1): 3-26. https://www.researchgate.net/publication/293767736