Perceptual And Arterial Occlusion Responses To Very Low Load Blood Flow Restricted Exercise Performed To Volitional Failure
We typically see that higher loads and magnitude of restriction pressure result in greater ratings of perceived exertion (RPE) and discomfort, as well as higher blood pressure responses. These factors are important because (1) the high levels of discomfort associated with high RPE may lead to poor adherence and (2)
the increased arterial pressure may be of concern especially for those with high or uncontrolled blood pressure.
While BFR training has been recommended for loads between 20-50% 1RM, not much is known about perceptual exertion, blood pressure response post-BFR, and volume workload responses to lighter loads (< 20% 1 RM). This study examined perceived effort and blood pressure responses in different load and occlusion pressure protocols.
Twenty-three college-aged individuals completed four exercise conditions varying in load and pressure. Each performed 4 sets of knee extensions to volitional failure (or 90 repetitions).
15% 1RM; no restrictive pressure
15% 1RM; 40% arterial occlusion pressure
15% 1RM; 80% arterial occlusion pressure
70% 1RM; no pressure
A ~30% increase in blood pressure was observed post exercise in the BFR conditions compared to the free flow conditions, suggesting that there may be a stronger circulatory stress response following BFR exercise (although still within safe parameters). The authors state that, “it does seem that applying blood flow restriction may augment the arterial occlusion/blood pressure response to resistance exercise, but not to an extent that would be considered dangerous for most individuals.”
Lower loads, as opposed to applied occlusion pressure, tend to be the primary driver of increased RPE when exercise is performed to volitional failure. A drop in volume did not cause a drop in RPE when BFR was applied, so it appears that it is not volume, but the magnitude of fatigue that determines RPE. Higher pressures and proximity to failure appear to increase RPE more so than volume. Depending on the individual, high loads may be more favorable due to less perceived effort.
The authors state, “Blood flow restriction may reduce the volume necessary to reach volitional failure, but it does so at an increased discomfort.” For individuals who are incapable or unwilling to lift heavier loads, blood flow restriction can be a useful tool to help reduce the amount of volume needed to reach volitional failure. For individuals experiencing high levels of discomfort, reducing the occlusion pressure may help improve adherence and overall tolerance to exercise. Once again, we see that BFR has the potential to be a bridge to heavier loading and assist in early rehabilitation.
Source: Dankel et al. (2018). Perceptual and arterial occlusion responses to vey low load blood flow restricted exercise performed to volitional failure. Clin Physiol Imaging. DOI: https://doi.org/10.1111/cpf.12535
****Remember, the decision to use BFR, or any treatment for that matter, should be based on the pillars of evidence-based practice.
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