Important Methodological Concerns for the Future of BFR Research

We at the BFR PROS recommend blood flow restriction (BFR) be used with low-intensity exercise (either aerobic or resistance training), as prior research (Laurentino, 2008) has indicated no additional benefit of BFR to heavy loads, likely due to the already heightened muscle activation and slow movement speeds inherent to lifting > 70% 1-rep max. However, a peculiar new just published study by Wang et al. (2022) challenges our commonly held beliefs on the topic. Let’s look at what they did and speculate on potential explanations for their findings.

Wang et al. (2022) enrolled 18 well-trained volleyball players (~20 years old) with resistance training experience and randomized them into one of three groups for the 8-week duration of the experiment: low-load BFR performed with 30% 1-rep max (n = 6), heavy load strength training with 70% 1-rep max (n = 6), and heavy load strength training with BFR using 70% 1-rep max (n = 6) performing backsquats 3x/week. BFR was applied at an estimated 50% arterial occlusion pressure (AOP) using an algorithm based on thigh circumference previously proposed by Loenneke’s group (Loenneke, 2012) and 4 sets of exercise were performed in the commonly recommended BFR fixed repetition scheme of 30-15-15-15 with 60 seconds of interset rest. BFR was applied to the bilateral thighs using B-STRONG™ cuffs and was applied continuously (was inflated before the exercise and released after the exercise only). Heavy load strength training with and without BFR was done for 4 sets of 8 repetitions with 60 seconds of interset rest. The major outcomes of the investigation were knee flexion/extension muscle strength (assessed with a backsquat 1-rep max and isokinetically at 60 degrees/second) and vertical jumping ability (assessed with a squat jump without arm countermovement and a three- footed takeoff jump – where the athletes took three steps, utilized a countermovement and then jumped).

After 8 weeks (24 sessions), athletes were retested, and the results were potentially noteworthy given the response of BFR during heavy load strength training. For muscle strength, 1-rep max backsquat strength improved for all groups compared to baseline, but the heavy load strength training group with- (+28.6%) and without BFR (+17.3%) improved more than the low load BFR group (+9.9%) with a non-significant trend (p = 0.071) for the heavy load BFR strength training group above heavy load strength training alone. Peak left and right knee extension isokinetic strength improved +5.1%/+8.6% in the low-load BFR group from baseline compared to +11.7%/+12.9% in the heavy load strength training group without BFR and +17.1%/+17.7% in the heavy load strength training with BFR group. Significantly greater increases in both heavy load strength training groups were observed compared to low-load BFR exercise, with no differences (p < 0.05) between heavy load groups. For left/right peak knee flexion torques, a similar trend was observed with both heavy load groups (+10.9%/+13.2% in heavy loads without and +16.5%/+15.9% with BFR) improving greater (p < 0.05) than low-load BFR exercise (+5.5%/+8.7%) with no differences between heavy load groups. Jumping performance as assessed by a squat jump improved only in the heavy load group with BFR, which was significantly greater than low-load BFR, but not heavy load strength training, post- intervention. Last, a similar trend was also observed in the three-footed takeoff jump as the heavy load group with BFR outperformed the low-load BFR group and was significantly higher than baseline but displayed similar overall changes to the heavy load strength training group without BFR. The results of this study support the use of BFR during heavy load strength training to improve not only muscle strength but also jumping performance compared to low- intensity BFR strength training. Or does it?

BFR is restriction of arterial blood supply to the working muscle and occlusion of venous return (Patterson, 2019). Prior research on heavy load strength training has used either practical BFR (knee wraps) (Cook, 2014) or single-chambered systems (Laurentino, 2012) and have mixed results on both augmenting strength as well as performance. The results of this study therefore, are surprising given the training status of the participants, the performance of a multi-joint exercise (the squat) for 75 repetitions at 30% of 1-rep max, and the applied pressure (180 mm Hg). If BFR exercise could augment performance, maybe there is another application that is available for athletes to train in the offseason to further their gains!

Unfortunately though, the authors really missed the mark with their BFR prescription because they failed to consider that B-Strong™ is a multi-chambered bladder system designed to not occlude. In fact, the recommended pressures for the lower body according to B-Strong™ is 350 mm Hg (Early, 2020). In addition, Citherlet et al. (2022) showed that femoral blood flow was unaltered from resting conditions at pressures as high as 300 mm Hg using B-Strong™, a pressure that is almost double to that used in this study (180 mm Hg). This is important as there appears to be a minimum amount of applied pressure (~50% AOP) needed to induce fatigue accumulation during BFR exercise (Cerqueira, 2021). The pressures used in this study likely did not alter resting blood flow to induce any effect related to the BFR stimulus and therefore the results indicate that the study did not actually measure the impact of BFR, but bilateral limb compression. Prior research has shown that limb compression enhances maximal strength to a greater degree than when performed without (Baum, 2020) which aligns with the results of the current study. We already know that when compared in a program, heavy load strength training will more than likely outperform low-intensity BFR exercise in strength and practical experience also supports that heavy load strength training will induce greater performance changes than low-intensity exercise with- and without BFR. I think its plausible to hypothesize that the bilateral stimulus applied to the legs during the backsquat exercise enhanced some form of stretch reflex in the working muscles beyond that of heavy load strength training alone. Unfortunately, as muscle activation and velocity were not measured, it leaves many questions unanswered.

Therefore, we cannot conclude that BFR in addition to heavy load strength training is superior to heavy load strength training alone because BFR was likely not achieved with adequate restriction pressures. Applying the pressure meant for a single-chambered bladder system to a multi-chambered bladder system is a very noticeable symptom of the exploding interest in studying BFR (which is great!) but not truly understanding what makes an effective restrictive stimulus (using a single-chambered bladder system) and a disregard of cuff design/features.

Unfortunately, as BFR continues to gain more popularity, I am seeing more studies designed whose methodologies convey that the researchers do not understand the nuances associated with cuff design (for example, single- versus multi-chambered bladders) and their associated features (for example, autoregulation). This muddles the water with our understanding of what BFR does and does not do because these studies will eventually be meta-analyzed and if this trend continues, we risk making unsupported conclusions based on poorly-designed studies simply because they failed to account for cuff design.

I feel so strongly about this, I wrote a paper on cuff designs and features that you can access here (Rolnick, 2022). It is my hope that highlighting shortcomings in the research particularly as it pertains to cuff design can help improve future research studies. The manuscript I wrote is under review and hopefully will be published eventually and maybe, just maybe, will shape the future of how we study BFR beyond just its clinical applicability.

In conclusion, the results of the study are more in line with intra-exercise compression therapy rather than BFR per se. I’d be more impressed with the results if they used a single- chambered system.

Until the next post….#ChaseThePump!

Study Citation:

Wang J, Fu H, QiangZhang, Zhang M, Fan Y. Effect of leg half-squat training with blood flow restriction under different external loads on strength and vertical jumping performance in well-trained volleyball players. Dose Response. 2022;20(3):15593258221123672.

References:

Laurentino G, Ugrinowitsch C, Aihara AY, et al. Effects of strength training and vascular occlusion. Int J Sports Med. 2008;29(8):664-667.

Patterson SD, Hughes L, Warmington S, et al. Blood flow restriction exercise position stand: Considerations of methodology, application, and safety. Frontiers in Physiology. 2019;10(MAY):533. doi:10.3389/fphys.2019.00533

Cook CJ, Kilduff LP, Beaven CM. Improving strength and power in trained athletes with 3weeks of occlusion training. Int J Sports Physiol Perform. 2014;9(1):166-172.

Early KS, Rockhill M, Bryan A, Tyo B, Buuck D, McGinty J. Effect of blood flow restriction training on muscular performance, pain and vascular function. Int J Sports Phys Ther. 2020;15(6):892-900.

Citherlet T, Willis SJ, Chaperon A, Millet GP. Differences in the limb blood flow between two types of blood flow restriction cuffs: A pilot study. Front Physiol. 2022;13. doi:10.3389/fphys.2022.931270

Cerqueira MS, Lira M, Mendonça Barboza JA, et al. Repetition failure occurs earlier during low-load resistance exercise with high but not low blood flow restriction pressures: A systematic review and meta-analysis. J Strength Cond Res. 2021;Publish Ahead of Print. doi:10.1519/JSC.0000000000004093

Baum JT, Carter RP, Neufeld EV, Dolezal BA. Donning a novel lower-limb restrictive compression garment during training augments muscle power and strength. Int J Exerc Sci. 2020;13(3):890-899.

Rolnick N, Kimbrell K, De Queiros V. Beneath the cuff. Published online August 13, 2022. doi:10.51224/srxiv.185 

****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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