Manipulating BFR Parameters
February 11, 2021
As more and more papers come out using a variety of parameters for BFR interventions we are routinely asked if we have new protocols to share. From our perspective, any and all protocols have flaws, and oftentimes those flaws are rather large and unavoidable. Thus, we generally try to avoid them, opting instead to teach principles of exercise prescription and how to adjust those in relation to BFR. In reading a recent paper written to summarize the existing literature on BFR endurance exercise, a line from the paper prompted me to try and map out the many variables and criteria one should have a mastery of in order to manipulate a BFR intervention in a comprehensive manner. Ferguson et al wrote, “In many respects, the permutations of intensity and duration of exercise and the application of BFR are endless.”(Ferguson et al., 2021) Below is a list of most of the variables you can manipulate for a given exercise session:
Probable BFR Exercise Variables:
- Pressure: Percentage of Limb Occlusion Pressure
- Pressure Application: Continuous or Intermittent
- Rep / set scheme
- Load progression / regression
Any number of factors could play into why you might adjust the aforementioned variables. For example, perceptual responses like discomfort could be addressed via pressure reduction until tolerance increases; another strategy could be to deflate between sets two and three. Difficulty completing the rep / set scheme could be the result of the load being too heavy, or perhaps the task itself was just too complex or difficult.
In today’s Instagram world, an oft perpetuated myth is that the more complex and “cool” an exercise is, the more effective it is. These “circus bear exercise feats” are often followed by some word salad explanation that is very confident, and in effect hypnotizes the reader into thinking the author must clearly know more than the reader regarding exercise prescription. Well, the good news is that exercise does not need to be complex in order to create changes in muscle size and strength. In fact, the more complex an exercise, the more varied the adaptations or lack thereof may be. A nice example of that can be found in the paper we reviewed on our most recent podcast. The authors described why they favored a single joint strength assessment over a multi-joint assessment as follows, “...and single joint > multiple joint strength test. This approach was chosen in order to minimize outcome variability by favouring low exercise neuromotor difficulty (e.g. knee extension > leg press).”(Grønfeldt et al., 2020) The more complex an exercise task, the more options there are for how to complete it. This has also been detailed very nicely in two papers from researchers at USC who showed that even to the trained eye, picking up on how someone alters their strategy to complete a task as simple as a squat is virtually impossible.(Chan & Sigward, 2019, 2020)Thus, in order to force a muscle to work hard enough to elicit a change, at minimum one must consider if there’s an escape for that muscle via an alteration in strategy, and control for it by constraining the movement.
Effective exercise prescription requires that you have a goal for the exercises you choose. Presently, some treatment and parameter targets with BFR that have an established evidence base are pain reduction, or increases in endurance, hypertrophy, or strength. Hughes et al have indicated that higher pressures may play a role in the magnitude of hypoalgesia (Hughes & Patterson, 2020), while guidance for the latter three was nicely detailed in the 2019 methodology paper spear-headed by Stephen Patterson, PhD.(Patterson et al., 2019) Other goals for the intervention are of course possible, but at least one of these should comprise the reason for choosing BFR.
In addition to having a treatment and / or parameter target based on current evidence, inherent limitations in rehab will result in the clinician inevitably encountering scenarios where BFR may be used in a strategic fashion to progress toward more optimal parameters, or progress away from the intervention altogether. This is why we’d suggest having a performance as well as a progression target to help you determine when to modify the intervention. With that in mind, simple aerobic type tasks can serve as a bridge to more traditional isotonic interventions as the patient gains ROM, and the ability to complete a high volume of work. Those early visits with low level activity can be used to familiarize w/ pressure as well as with engaging fatigue at a lower intensity than will ultimately be necessary to build muscle. Early phase interventions like combining BFR w/ NMES can also contribute in this way, but could have a place later in rehab as a finisher too.
Some simple adjustments to variables can help the clinician gain buy-in from his or her patient, while exposing them gradually to an intervention. If you’re like me, you probably undershoot the load initially. This can work well as an introduction to BFR though. It does however require that you be mindful of effort and progress load as soon as possible. I watch rather intently how well my patient completes their last set of 15. Did I have to encourage them, did I have to assist them, or did they finish with just some minor effort? These are questions that help me determine how to adjust their next visit. If they make all 75 reps 2 visits in a row, load goes up. Sometimes it is obvious you have undershot and merely adding exercise volume to get more effort on the fly is certainly an option. Then make a note to progress the load the next visit. Other times a patient might really be having a tough time with the pressure. In those cases you can of course reduce the pressure, but you could also fully deflate during the rest period (to do this with a Delfi, disconnect the hose from the cuff and cover it with your thumb...pushing deflate will force a 1 minute rest). That’s just a sampling of how to think through your BFR exercise. Below you will also find a sample of a chart I made to help me think through the many variables I need to be attending to and modifying!
Chan, M.-S., & Sigward, S. M. (2020). Center of pressure predicts Intra-limb compensatory patterns that shift demands away from knee extensors during squatting. Journal of Biomechanics, 110008.Chan, M.-S., & Sigward, S. M. (2019). Loading Behaviors Do Not Match Loading Abilities Postanterior Cruciate Ligament Reconstruction. Medicine and Science in Sports and Exercise, 51(8), 1626–1634.
Ferguson, R. A., Mitchell, E. A., Taylor, C. W., Bishop, D. J., & Christiansen, D. (2021). Blood-flow-restricted exercise: Strategies for enhancing muscle adaptation and performance in the endurance-trained athlete. Experimental Physiology. https://doi.org/10.1113/EP089280
Grønfeldt, B. M., Lindberg Nielsen, J., Mieritz, R. M., Lund, H., & Aagaard, P. (2020). Effect of blood-flow restricted vs. heavy-load strength training on muscle strength: Systematic review and meta-analysis. Scandinavian Journal of Medicine & Science in Sports. https://doi.org/10.1111/sms.13632
Hughes, L., & Patterson, S. D. (2020). The effect of blood flow restriction exercise on exercise-induced hypoalgesia and endogenous opioid and endocannabinoid mechanisms of pain modulation. Journal of Applied Physiology. https://doi.org/10.1152/japplphysiol.00768.2019
Patterson, S. D., Hughes, L., Warmington, S., Burr, J., Scott, B. R., Owens, J., Abe, T., Nielsen, J. L., Libardi, C. A., Laurentino, G., Neto, G. R., Brandner, C., Martin-Hernandez, J., & Loenneke, J. (2019). Blood Flow Restriction Exercise: Considerations of Methodology, Application, and Safety. Frontiers in Physiology, 10, 533.