How Hard Should You “Squeeze”?: A Review into Blood Flow Restriction Training on Powerlifting

Introduction

In powerlifting, marginal advantages over competitors may be the difference between winning and losing [16]. As such, many training methods have been developed to maximize strength output. One such approach is blood flow restriction training (BFRT). Developed in Japan in 1966 by Yoshiaki Sato, BFRT involves low-load, high-repetition exercise with restriction cuffs applied to the proximal ends of limbs [1]. These cuffs effectively restrict blood flow to working muscles, thus increasing mechanical tension and metabolic stress [20]. Blood flow restriction is characterized by arterial occlusion pressures (AOP), which are pressures corresponding to the amount of blood restricted within a vessel. High AOPs create a hypoxic environment in which hypertrophic pathways are upregulated [3]. Elevation of these responses leads to enhanced muscle fiber repair post-exercise [20].

This anabolic state is often achieved with conventional heavy weight training, a state that lightweight BFRT aims to recreate [1]. The efficacy of clinical low-load BFRT for post-op patient rehabilitation has long been acknowledged and utilized since 2006 [11]. Since then, additional clinical studies have shown blood flow restriction (BFR) greatly benefits individuals who are unable to perform heavy-weight exercise [12], [15]. However, there is currently little research on the application of this method in heavy-load training programs. Unlike clinical BFRT, mechanisms of BFRT that elicit strength are still unclear. Hence, this review will investigate the effects of BFRT on maximal strength, muscle hypertrophy, and the relationship between AOP and different limb circumferences.

Key Words: Blood flow restriction (BFR), blood flow restriction training (BFRT), arterial occlusion pressure (AOP), restriction cuffs, maximal strength, muscle hypertrophy, limb circumference 

BFRT and Upper Limbs

The bench press is a staple multi-joint exercise to assess upper body strength [21]. BFRT at high AOPs showed significant strength increases for this exercise; however, how it elicits these gains remains inconclusive. To study this, Gepfert et al. (2021) examined the effects of external compression on peak bar velocity (PV), time under tension (TUT), and maximum repetitions (MR) during the BP exercise. Cuff pressures were set to 70% AOP and were applied continuously throughout the sets. Results found no significant increases in any of the metrics of interest. Hence, the research team concluded that BFR does not have any benefits on BP performance, nor does it have any negative effects. In a similar 2019 study, Rawska et al. explained that BFRT increased performance not only through enhanced metabolic stress but also through mechanical work generated by the cuff itself. Because restriction cuffs are elastic, their compression leads to a rebound effect which could physically aid the lifter in the concentric part of the lift. Therefore, it is possible that the restriction pressures used by Gepfert et al. were too low to elicit any noticeable strength gains. 

In contrast, Wilk et al. (2020 (A)) looked into the effects of BFRT on BP performance at occlusion pressures over 100%. At 100% AOP, restriction cuffs completely cut off blood flow to muscles. This study used the same setup and methodologies as Gepfert et al. (2021); the only difference being that pressures were set to 150% AOP instead of 70% AOP. After 7 weeks of training, participants’ one rep maxes (1RM) were measured, along with their PV, TUT, and MR. Results found significant increases in all categories between the control group and the 150% AOP group, which contradicts Gepfert et al. findings. Comparing 70% AOP and 150% AOP, the former permits some level of blood flow; whereas, the latter not only completely cuts off blood flow, but also exerts additional pressure onto the muscles. 150% AOP ensures that the muscle is completely fatigued, thus ensuring metabolic stress is properly induced. Research suggests that at extremely high AOPs, BFRT is highly effective at increasing total force production. However, whether it does so by enhancing physiological responses or adding mechanical energy still needs to be distinguished.

BFRT and Lower Limbs

Heavy-load BFRT is successful in increasing maximal power output in the squat exercise - a staple assessment of lower limb strength. Godawa et al. (2012) aimed to see whether BFRT allowed athletes to lift heavier loads by assessing their total weight lifted. Collegiate competitive lifters were randomly split into 2 groups: Compressive Gear and Non-Compressive Gear. These groups underwent 10 weeks of strength training with identical loading programs, after which, back squat, bench, and deadlift were tested for 1RM. Results found significant increases in back squat 1RM alone, while bench and deadlift gains were negligible. This result does not contradict prior statements on BFRT and upper limbs, since researchers did not use restriction cuffs for the arms and opted for compression sleeves instead. The performance gains from this study were noteworthy, as the average improvement of the Compressive Gear over 10 weeks was similar to athletes training conventionally for a year. Further measurements into the back squat showed significant reductions in popliteal flow under BFR conditions, suggesting a connection between blood flow occlusion and strength gains. Although researchers concluded that the lack of blood flow increased powerlifting performance, the underlying cause is still unknown.

A possible explanation for BFRT strength-enhancing mechanisms could be increased muscle hypertrophy. BFRT induces metabolic stress that grows bigger muscles capable of lifting more weights. To study this, Bjornsen et al. (2019) used muscle cross-sectional area analysis to measure muscle sizes between a BFRT group and a control group. Researchers found that after a 6.5 week front squat program, participants under BFR conditions not only exhibited greater thigh circumferences and increased muscle thickness but also an increase in the amount of weight lifted. Utilizing muscle biopsy and ultrasound imaging, multiple studies also confirmed the hypertrophic benefits of BFRT: Increased cross-sectional areas of major thigh muscles [3] and increased overall limb circumference [1]. Muscle fibers are categorized into two main types: Type I dominates slow, endurance contractions, while Type II dominates rapid, explosive contractions. Under normal conditions, heavy load strength training preferably recruits type II muscle fibers which exert more force over a shorter time period [6]. However, analysis from Bjornsen et al. revealed that the hypertrophic effect came from type I muscle fibers, not type II. BFRT seems to preferentially target type I muscle fibers whose functions are entirely opposite. This discrepancy in muscle recruitment can be explained by increased rates of type I protein heat shock and glycogen depletion under hypoxic conditions [10]. Cumulatively, these findings not only support the efficacy of BFRT in lower limb strength but also suggest BFRT as a novel stimulus for powerlifters who have hypertrophied fast twitch muscle fibers. 

Discussion on AOPs and Limb Circumference

The efficacy of BFRT ultimately depends on the relationship between limb circumference and AOPs. Gepfert et al. (2020) looked into back squat performances in training groups with restriction cuffs placed at the proximal ends of the legs. Although AOPs varied among the groups, cuff placement completely cut off blood flow from the tibial artery, ensuring similar metabolic stress among the groups. Participants were divided into three groups with three different pressures: 0% AOP (control - no cuffs), 100% AOP (173+-17mmHg), and 150% AOP (256+-26mmHg). Results found a significant increase in power output and bar velocity in the 150% AOP group compared to the rest. Among the remaining two groups, no significant differences were found. These findings suggest that the magnitude of external compression played a role in the increased performance. Wilk et al. (2020 (A)) also found similar results for upper limb bench press performance. Similar to Gepfert et al., Wilk's team also applied three different restriction pressures to the proximal ends of both arms: 0% AOP (control), 100% AOP (135+-16mmHg) and 150% AOP (202+-23 mmHg). Results found that the 150% AOP group had significantly increased their one rep max (1RM) compared to the other groups. This group could also perform significantly more repetitions in one set, suggesting an increase in strength endurance as well. Again, no differences were found between control and 100% AOP. Although Gepfert et al. (2020) and Wilk et al. (2020 (A)) looked at two different areas of the body, they both concluded that different limbs require different levels of absolute AOP to elicit similar strength gains. This coincides with Gepfert et al. (2021) discussion: The smaller circumference of upper limbs requires a smaller absolute pressure to produce the same effect as their lower body counterparts. In addition, the frequency and length of blood flow restriction application also affect results (Wilk, 2020 (B); Wilk, 2020 (C)). Gepfert et al. (2021) and Wilk et al. (2020 (A)) only applied BFR for a short training period (6.5 weeks). Both also applied the equipment right before and took them off right after participants finished their sets. Although this method ensured that target muscles were properly fatigued, the duration of metabolic stress might have not been enough to investigate the extended physiological effects of BFRT. 

Potential side effects of BFRT

Concerns arise that at such intense AOP, BFRT could lead to muscle damage in regions directly under the cuff, posing a big risk of physical impairment [5]. A 13,000-patient Japanese survey reported BFR-related complications such as bruising (13%), numbness (1.3%), thrombosis (0.06%), and embolism (0.008%) [11]. To measure the levels of myotrauma/inflammation, past studies have shown that plasma proteins are reliable biomarkers for muscular injury [14]. Applying this knowledge, Clark et al. (2010) investigated plasma protein levels between BFRT groups and non-BFRT groups. Researchers collected blood samples 1 hour after training sessions and analyzed differences among a wide collection of plasma protein concentrations (Fibrinogen, D-dimer, tPA antigen, and C-reactive protein). Data showed no significant changes in any of these biomarkers’ concentration levels. Similarly, Winchester et al. (2020) also used the same methodology but focused specifically on Myoglobin and Interleukin-6. These two plasma proteins promote leukocyte chemotaxis through the mobilization of satellite cells, which is critical for muscle repair [20]. Data analysis found no significant differences between the two groups. Both research teams concluded that BFRT increases rates of muscle fatigue while not causing muscle damage or inflammation responses. Collectively, these findings indicate that BFRT does not negatively affect vascular stiffness, peripheral nerve conduction, or blood clotting functions. It has to be noted that both of these studies only applied BFR for the short duration of the experiment, so the effects of continuous pressure over a prolonged period have not yet been determined. Researchers expect that frequent exposure to extremely high muscle compression could lead to adverse/irreversible effects.

Conclusion

The application of BFRT in heavy-load strength training increases both maximal strength and muscle hypertrophy in the upper and lower limbs. Several studies show how extremely high AOPs can induce metabolic stress that results in enhanced powerlifting performance. Muscle analysis also revealed that BFRT offers great hypertrophic benefits with minimal muscle damage or inflammation. Recruitment of different muscle types provides coaches and strength athletes with novel ways to elicit greater strength feats while avoiding muscle imbalances. In contrast to low-load, high-repetition BFRT, heavy-load BFRT also allows individuals to train accessory exercises (non-competition lifts) at lower repetitions, thus minimizing fatigue while still yielding competitive results.  

However, most of the studies fail to fully separate the physiological effects from the mechanical work provided by elastic restriction cuffs. The presented studies all support that BFRT increases powerlifting performance, but this increase could stem exclusively from one of the mentioned effects, or even both simultaneously. A better understanding of BFRT’s physiological effects will help solidify the safety of prolonged, continuous BFRT utilization. In addition, further investigation into restriction cuff mechanical recoil will help lifters fully utilize BFRT short-term effects for geared-competition lifts. Either way, future research should include health adaptations for long-term BFRT usage and focus on developing new methods to qualitatively study the aforementioned effects individually.

About the Author: Duong Hoang

My weightlifting journey started when I entered UC Davis. Starting out from general bodybuilding and then transitioning into powerlifting, I started using compressive equipment like sleeves, cuffs, and belts to aid my training. Being under induced pressure and stress seemed to promote muscle hypertrophy, by which my muscles grew stronger than before. I have learned about these mechanisms in my NPB major classes, but have never really gotten the chance to investigate these mechanisms meta-analytically. Therefore, when presented with the opportunity as a UWP102B assignment, I chose to compile all the recent research into one big literature review to shed light on all the areas that I did not understand. I hope this paper will be an interesting topic for readers and inspire future research on blood flow restriction training. 

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