Acute Perceptual & Muscle Activation Responses Between Delfi, B-Strong and High Load

As more and more BFR devices come to market it is quite useful for independent investigators to examine the performance of these devices. This allows the consumer to make a more educated decision when seeking to determine what is the best choice for their setting and clientele. It is however very important that these trials are conducted in a manner that allows outcomes to be compared.(1)

Recently, Bordessa et al examined the acute effects of low intensity BFR knee extensions with two different BFR devices against a heavy load control.(2) The BFR interventions were provided by an unregulated handheld pump device (B-Strong), and a regulated device (Delfi). The loads utilized were 30% and 80% 1RM and the outcomes measured were muscle activation (peak and mean EMG), RPE (Omni-Res), and pain via the Numeric Pain Rating Scale (NPRS). The researchers found no difference in mean or peak muscle activation between the BFR groups, but a significantly greater EMG response for the high load group. Additionally, Delfi was found to be associated with greater pain and RPE than either the B-Strong or heavy loaded groups; while the B-Strong group was associated with a significantly greater pain and RPE than the heavy load group.

The major limitation of this study is the failure of the design to ensure both BFR groups received the same or even similar levels of blood flow restriction. This limitation alone calls into question any comparison of acute responses between the two devices. The Delfi device uses a research validated measurement of occlusion pressure and accurate pressure regulation throughout an exercise.(3) This approach to applying BFR pressure is generally accepted by the medical and research communities as the gold standard.(4,5) To our knowledge there have been no trials conducted using B-Strong to validate its means of determining pressure. Given the marketing and reported design of the B-Strong device that, “it will never occlude”, raises the question whether or not an individualised pressure could ever be determined using that device.

A number of factors are reported to be taken into account for the pressure used by the B-Strong device: age, gender, overall health, size of the strap used, limb girth and preferred intensity level. Importantly, of the variables considered, only the effect limb girth has on LOP has been studied. When used with a narrow cuff like B-Strong, limb girth only explained 15% of the variance in LOP.(6) Without controlling for the magnitude of restriction, one is unable to determine if the findings or lack thereof, are a result of a difference in the amount of restriction or because one device is regulated and the other is not. This would be synonymous with looking at the effects of two different pain relievers without being mindful of the dosage of each.

While the EMG data is interesting, the findings of greater discomfort and RPE were predictable given the comparison of a high relative pressure (80% LOP) against an arbitrary pressure from a cuff that is less than half the width of Delfi.(7) Acutely, this appears to be closely related to the absolute pressure of the tourniquet when the same relative load is used.(8,9) However, over a training period, this response is diminished and similar to that achieved by high load resistance training.(10,11) Nevertheless, during the initial few sessions, if the pressure is not well tolerated, the clinician can employ a couple strategies to address this. When utilizing a low load (20% 1RM), initially starting with a lower pressure, such as 60% LOP and gradually progressing back towards 80% can allow individuals to acclimate to the pressure, making the 80% LOP more tolerable when reached. In addition to modifying the percentage of occlusion during the exercise, the clinician can keep the pressure high during the exercise and decrease the pressure to 40% LOP during the 30 second rest period. This approach will make the rest period more tolerable, but maintains full venous occlusion so the metabolites accumulated during the exercise are not flushed out of the muscle.

Surface EMG amplitudes are commonly collected and compared between exercise techniques or loads. Based on these acute comparisons, researchers attempt to extrapolate findings into longitudinal changes in muscle mass or strength. However, the longitudinal relevance of acute EMG responses has recently been questioned.(12) It would also appear from Morton et al that the chief determinant of EMG amplitude is the relative load being lifted. The findings of Bordessa et al certainly seem to support this. Previous research indicates there are numerous parameters ranging from cuff width, relative occlusion pressure, and effort, which strongly influence muscle activation, lactate accumulation and ultimately muscle hypertrophy.(6,13–15) By only looking at muscle activation, one is unable to accurately assess how much effort was exerted by the muscle and if the effort exerted was sufficient to produce an anabolic effect that would subsequently lead to an increase in muscle hypertrophy throughout a training period. Recent research strongly suggesting there are comparable increases in muscle mass over a resistance training period when a similar volume (weight*total reps) is performed, regardless of the load lifted.(16) Given this, one must ultimately question the overall value of EMG data as it relates to a stimulus being sufficient to cause a desired adaptation.

In conclusion, when using low loads, the exercise must be taken close to the point of failure, to produce similar hypertrophic results to high load training. An important component to this when performing low load BFR exercises is doing the entire protocol (30/15/15/15) and ensuring a proper pressure is utilized (60%-80% LOP). When looking at the effect of BFR, it is important to establish a relative pressure for each individual, this will ensure all individuals receive an objective, repeatable stimulus. Lastly, when prescribing an intervention to an individual, the clinician should always consider what the goal of the treatment is and how is this going to accomplish an overall treatment outcome. Many of the issues faced in a clinical setting are a result of muscle disuse. The primary goal to address this acutely is to perform a resistance exercise that significantly increases muscle protein synthesis, longitudinally this will increase muscle hypertrophy and contribute to an increase in strength. Both adaptations can be accomplished regardless of the load lifted, as long as the individual performs the lift close to the point of fatigue.

1. Rolnick N, Cerqueira MS. Comparison of Blood Flow Restriction Devices and Their Effect on Quadriceps Muscle Activation: Letter to the Editor. Phys Ther Sport. Published online March 22, 2021. doi:10.1016/j.ptsp.2021.03.006

2. Bordessa JM, Hearn MC, Reinfeldt AE, et al. Comparison of Blood Flow Restriction Devices and Their Effect on Quadriceps Muscle Activation. Phys Ther Sport. Published online February 12, 2021. doi:10.1016/j.ptsp.2021.02.005

3. Masri BA, Day B, Younger ASE, Jeyasurya J. Technique for Measuring Limb Occlusion Pressure that Facilitates Personalized Tourniquet Systems: A Randomized Trial. J Med Biol Eng. 2016;36(5):644-650.

4. Patterson SD, Hughes L, Warmington S, et al. Blood Flow Restriction Exercise: Considerations of Methodology, Application, and Safety. Front Physiol. 2019;10:533.

5. Day B. Personalized Blood Flow Restriction Therapy: How, When and Where Can It Accelerate Rehabilitation After Surgery? Arthroscopy. 2018;34(8):2511-2513.

6. Loenneke JP, Fahs CA, Rossow LM, et al. Effects of cuff width on arterial occlusion: implications for blood flow restricted exercise. Eur J Appl Physiol. 2012;112(8):2903-2912.

7. Rossow LM, Fahs CA, Loenneke JP, et al. Cardiovascular and perceptual responses to blood-flow-restricted resistance exercise with differing restrictive cuffs. Clin Physiol Funct Imaging. 2012;32(5):331-337.

8. Mattocks KT, Mouser JG, Jessee MB, et al. Perceptual changes to progressive resistance training with and without blood flow restriction. J Sports Sci. 2019;37(16):1857-1864.

9. Dankel SJ, Jessee MB, Mattocks KT, et al. Perceptual and arterial occlusion responses to very low load blood flow restricted exercise performed to volitional failure. Clin Physiol Funct Imaging. 2019;39(1):29-34.

10. Teixeira EL, Painelli V de S, Schoenfeld BJ, et al. Perceptual and Neuromuscular Responses Adapt Similarly Between High-Load Resistance Training and Low-Load Resistance Training With Blood Flow Restriction. J Strength Cond Res. Published online December 9, 2020. doi:10.1519/JSC.0000000000003879

11. Martín-Hernández J, Ruiz-Aguado J, Herrero AJ, et al. Adaptation of Perceptual Responses to Low-Load Blood Flow Restriction Training. J Strength Cond Res. 2017;31(3):765-772.

12. Morton RW, Sonne MW, Zuniga AF, et al. Muscle fibre activation is unaffected by load and repetition duration when resistance exercise is performed to task failure. J Physiol. Published online July 11, 2019. doi:10.1113/JP278056

13. Laurentino GC, Loenneke JP, Teixeira EL, Nakajima E, Iared W, Tricoli V. The Effect of Cuff Width on Muscle Adaptations after Blood Flow Restriction Training. Med Sci Sports Exerc. 2016;48(5):920-925.

14. Stray-Gundersen S, Wooten S, Tanaka H. Walking With Leg Blood Flow Restriction: Wide-Rigid Cuffs vs. Narrow-Elastic Bands. Front Physiol. 2020;11:568.

15. Ilett M, Rantalainen T, Keske M, May A, Warmington S. The Effects of Restriction Pressures on the Acute Responses to Blood Flow Restriction Exercise. Front Physiol. 2019;10:1018.

16. Schoenfeld BJ, Grgic J, Ogborn D, Krieger JW. Strength and Hypertrophy Adaptations Between Low- vs. High-Load Resistance Training: A Systematic Review and Meta-analysis. J Strength Cond Res. 2017;31(12):3508-3523.