The Exercise Pressor Reflex: Should We Be Concerned? Part 2

 

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The Exercise Pressor Reflex: Should We Be Concerned? Part 2
Nicholas M. Licameli, PT,DPT

 

 

 

 

Welcome back! As promised, here is part two of our dive into the exercise pressor reflex (EPR). I know!  So exciting!  Let’s go!

 

BE SURE TO CHECK OUT PART 1 BEFORE PROCEEDING, but just to quickly review, the EPR is the exaggerated cardiovascular response to exercise proportional to the level of intensity of that exercise.  This can be a barrier to the widespread usage of BFR, especially for patients and athletes with comorbidities.  There are, however, ways to mitigate the EPR and in Part 1, I introduce four ways to do just that.  They are (1) avoiding exercises that require a strong valsalva maneuver, (2) selecting cuff pressures that are on the low end of the range of effectiveness and using intermittent BFR, (3) choosing dynamic over static exercises while avoiding failure, (4) and performing exercises that use small muscle groups rather than large muscle groups.  Now it’s time to dive deep!

 

Avoiding Valsalva

Increased cardiovascular demand is well documented during non-BFR exercise. MacDougall et al showed that the increases in blood pressure and heart rate could be extreme when performing exercise at high intensities. When individuals performed bilateral leg press at 80-100% of their 1 rep max, blood pressure was measured as high as 480/350 mmHg and heart rate was as high as 170 beats per minute. (MacDougall et al., 1985). The authors considered that the significant increases in pressure and heart rate might have occurred as a result of mechanical compression of the vasculature and increased abdominal pressure via valsalva.  Therefore, to avoid excessive cardiovascular demand during BFR exercise, it may be wise for clinicians and coaches to educate their patients and clients to avoid valsalva.

 

Low Cuff Pressures and Intermittent BFR

Another consideration for modulating cardiovascular demand is pressure selection.  Brandner et al compared 130% of systolic pressure (intermittently) to 80% of systolic pressure (continuously) while performing a bicep curl exercise with 20% of a 1-rep max. They showed that the changes in blood pressure, heart rate, and mean arterial pressure are greater even when BFR is applied intermittently at a higher pressure (Brandner et al., 2015) (more on intermittent BFR later).  As explained by Rolnick et al, using an intermittent pressure system can decrease the exaggerated cardiovascular response to BFR training (Rolnick et al., 2021). Bradner et al saw greater cardiovascular demand using an intermittent pressure protocol, however they used 130% LOP, which is higher than what is typically recommended (Patterson et al., 2019).  Therefore, whether constant or intermittent, it is reasonable to conclude that using a low to moderate pressure can help reduce overall cardiac demand during BFR exercise.  

 

Dynamic vs. Static Exercise and Exertion

Another consideration regarding BFR and cardiovascular demand is exercise selection.  It appears that static exercise elicits a greater pressor response than dynamic exercise (Mitchell, et al., 1994).  Wilson et al, showed that exercise that involves contraction of fast twitch glycolytic fibers elicits a much larger pressor response than slow-twitch oxidative muscle (Wilson, et al., 1995).  Spranger et al notes that BFR hastens the recruitment of fast-twitch fibers, which may generate greater elevations in sympathetic activity and blood pressure than traditional exercise (Spranger et al., 2015).   So if you are planning on using dynamic exercise in order to limit the EPR, be sure to perform exercises in a way that does not tax the high threshold motor units.  This may come in the form of avoiding explosive movements or avoiding close proximity to failure. 

 

Small vs. Large Muscle Groups

Finally, Oliveira et al explains that exercises that involved larger muscle groups (legs) tend to have a higher pressor response than exercises that use smaller muscle groups (hand/forearm) (Cristina-Oliveira, et al., 2020).  If a patient or athlete has comorbidities and you would like to limit the EPR, try performing a calf raise or biceps curl rather than a squat or a push up.  

 

So there you have it, folks.  This two-part beast should supply you with enough knowledge to hold a conversation the next time the exercise pressor reflex comes up at a summer barbeque.  Kidding aside, this information can be extremely powerful for the safety of our patients, but also the education of other professionals.  Be sure to dive into the references in both Part 1 and Part 2 for a more in-depth explanation.

 

References

 

Brandner, C. R., Kidgell, D. J., & Warmington, S. A. (2015). Unilateral bicep curl hemodynamics: Low-pressure continuous vs high-pressure intermittent blood flow restriction. Scandinavian journal of medicine & science in sports25(6), 770–777. https://doi.org/10.1111/sms.12297.

 

Cristina-Oliveira, M., Meireles, K., Spranger, M. D., O’Leary, D. S., Roschel, H., and Peçanha, T. (2020). Clinical safety of blood flow-restricted training? a comprehensive review of altered muscle metaboreflex in cardiovascular disease during ischemic exercise. Am. J. Physiology-Heart Circulatory Physiol. 318, H90–H109. doi: 10.1152/ajpheart.00468.2019.

MacDougall JD, Tuxen D, Sale DG, Moroz JR, Sutton JR. Arterial blood pressure response to heavy resistance exercise. J Appl Physiol 58: 785–790, 1985.

Mitchell JH, Kaufman MP, Iwamoto GA. The exercise pressor re- flex—its cardiovascular effects, afferent mechanisms, and central path- ways. Annu Rev Physiol 45: 229–242, 1983. 

Patterson, S. D., Hughes, L., Warmington, S., Burr, J., Scott, B. R., Owens, J., et al. (2019). Blood flow restriction exercise: considerations of methodology. application, and safety. Front. Physiol. 10:533. doi: 10.3389/fphys.2019.00533.

Rolnick N, Kimbrell K, Cerqueira MS, Weatherford B and Brandner C (2021) Perceived Barriers to Blood Flow Restriction Training. Front. Rehabilit. Sci. 2:697082. doi: 10.3389/fresc.2021.697082.

Spranger, M. D., Krishnan, A. C., Levy, P. D., O’Leary, D. S., & Smith, S. A. (2015). Blood flow restriction training and the exercise pressor reflex: a call for concern. American journal of physiology. Heart and circulatory physiology309(9), H1440–H1452. https://doi.org/10.1152/ajpheart.00208.2015.

Wilson LB, Dyke CK, Parsons D, Wall PT, Pawelczyk JA, Williams 

RS, Mitchell JH. Effect of skeletal muscle fiber type on the pressor response evoked by static contraction in rabbits. J Appl Physiol 79: 1744 –1752, 1995.



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