INTRODUCTION

Traditional weight training protocols rely on heavy-load resistance to induce muscle hypertrophy and strength improvement. Conventionally, 70% of an athlete’s one-repetition maximum (1RM) has been considered necessary to achieve muscle hypertrophy. The high load activates and recruits more type II muscle fibers, which are more inclined to hypertrophy than type I fibers (1). Low-load training also can produce muscular hypertrophy, albeit with inferior results (2). Blood flow restriction (BFR) training is a unique addition to strength training protocols. Recent evidence indicates that the addition of BFR training to low-load resistance training can induce muscle hypertrophy and strength gains comparable with high-load resistance (3,4). The ability to achieve similar strength and hypertrophy gains with lighter resistance is especially beneficial in populations who cannot tolerate heavy-load resistance training, such as patients and athletes recovering from surgery or injury, or those suffering from frailty. Thus, BFR training has generated interest as an emerging tool for rehabilitation, strength training, and prevention of sarcopenia.

BACKGROUND

BFR training involves the limitation of blood flow through a restrictive device placed proximally to, or above, the target muscle group. The type of device used varies widely, but inflatable bands, elastic bands, and tourniquets are most common. The goal of BFR training is to inhibit venous outflow while maintaining arterial flow to the extremity (5). The BFR training technique arose in Japan in the late 1960s when Dr. Yoshiaki Soto first developed the concept of blood flow occlusion during training. He experimented with various devices and occlusion pressures before successfully using it on himself after suffering bilateral ankle fractures in a skiing accident. Protocols for what he termed “Kaatsu” training were published for public use in the early 1980s, spurring scientific research into the mechanisms and possible applications of what is now more commonly known as BFR training (6).

The precise mechanism of action of BFR training is unknown. It appears that the metabolic stress caused by limited venous return works synergistically with the mechanical stress of resistance training to mediate several autocrine and paracrine effects (7). Multiple other potential mechanisms have been proposed. For instance, BFR training causes elevated systemic hormone production, increased fast-twitch fiber recruitment, increased production of reactive oxygen species, greater buildup of anabolic metabolites, and increased cell swelling (7–11). Although each of these alone or in some combinations may contribute to the beneficial effects of BFR training, the mechanistic actions are not yet proven.

APPLICATIONS

The proper utilization of BFR training has been shown to induce muscle hypertrophy, muscle strength, and functional gains (4,12–14). A wide variety of applications have been studied, from resistance training to aerobic training, to static application for the prevention of muscle wasting. One of the most robustly evaluated applications uses BFR training in conjunction with low-load resistance training, or 20% to 30% of 1RM. As previously mentioned, low-load resistance training alone does not lead to significant muscle hypertrophy in most cases. However, many early studies have shown that the addition of BFR training to low-load training produces augmented hypertrophy and strength improvements compared with traditional low-load training (13), yet many of these early studies were performed with untrained or amateur athletes. In trained athletes, there is evidence of improved knee extension torque and muscular endurance after 8 weeks of low-load resistance BFR training (3), and also increased 1RM on bench press and squat testing using low-load BFR training compared with low-load training alone (15). Both of these studies demonstrated that there is likely some functional and strength benefit to low-load training with BFR training, even in trained athletes.

Despite this, it remains clear that strength and hypertrophy gains with low-load BFR training alone are not as substantial as traditional high-load resistance training, yet low-load BFR training does appear to yield better strength gains and more hypertrophy than low-load resistance training alone (16). This raises questions regarding the utility of low-load BFR training when weight training healthy elite athletes who are able to participate in traditional high-load programs. The available evidence seems to indicate a greater benefit for this group when low-load BFR training is used as a supplement to a traditional high-load training routine. This effect was best noted in a study using college football players, with those who added low-load BFR training to their traditional high-load lifting routines experiencing a greater increase in squat 1RM compared with several other groups, including traditional high-load resistance training alone (17). This strategy of combining traditional high-load resistance with supplemental low-load BFR training has possible applications for resistance training in athletes, facilitating more rapid gains in strength than with traditional high-load resistance training.

Beyond strength training, BFR training has several potential applications in the realm of rehabilitation. Acute and chronic injuries are known to lead to muscle weakness and atrophy. Low-load resistance training with BFR training has the potential to allow patients to begin rebuilding meaningful amounts of muscle earlier in the course of rehabilitation when they cannot tolerate high-load training. Low-load resistance training with BFR training also has shown benefit in postoperative rehab after ACL reconstruction and knee arthroscopy. Patients in the BFR training groups had significantly increased strength in the knee extensors and thigh cross-sectional area when compared with patients whose rehab included low-load resistance training alone (18,19). Similar strength and functional gains were seen in women older than 45 years with symptomatic knee osteoarthritis, which can be associated with muscle wasting due to chronic pain (20). Literature also suggests that BFR training may be applied statically to prevent muscle wasting from occurring in the first place. In fact, applying a daily occlusive stimulus, without any associated exercise, to a postoperative leg on days 3 to 14 after ACL surgery demonstrated significantly diminished knee extensor muscle atrophy when compared with controls (21). Further study is warranted, but these few published studies indicate that BFR training could be a useful tool in both the prevention of muscle wasting associated with acute and chronic injury and the more rapid recovery of muscle strength and volume during rehabilitation.

Another promising application for BFR training is among frail elderly, who can experience significant muscle atrophy as the result of muscle resistance to anabolic stimuli. It is often difficult to combat muscle wasting, as this population often has difficulty participating in high-load resistance training (22). However, low-resistance walking training with BFR training has been shown to increase muscular strength and functional ability in the elderly (12). Low-load resistance training with BFR training also has been shown to produce substantial strength and functional improvements. Significantly, these functional improvements were preserved even after a period of detraining (23). Thus, BFR training has shown possible benefits across multiple populations, from the elderly to the trained athlete. However, some of the more promising applications in the world of rehabilitation, strength, and functional maintenance appear to be in their infancy and warrant further investigation to determine the most appropriate and useful protocols.

SAFETY

As illustrated above, BFR training has been shown to be efficacious in various situations and populations. However, because of the cardiovascular manipulation inherent in BFR training, safety must be considered as well. Several questions have arisen regarding effects on vasculature, nerve conduction, muscle tissue, and the heart. Pooling of blood within the extremity could theoretically cause deep vein thrombosis or venous valve damage. However, there appears to be no evidence of this in the literature, and changes in vasculature appear to be similar to what is seen with standard exercise (24). In addition, muscle damage seems to be comparable with what is seen with traditional low-load resistance exercise, and there has been no evidence of any change in nerve conduction after BFR training (24). There have been a few case reports of rhabdomyolysis; however, incidence appear to be rare (25). Hemodynamic concerns also have been raised, which are especially relevant as BFR training is emerging as a potential cardiac rehabilitation tool. Current research has demonstrated that changes in heart rate and blood pressure appear to be less significant than with traditional high-resistance exercise. Although both responses are higher than in traditional low-load resistance training, the changes are very small and unlikely to be significant (26). All in all, adverse events have been rare, and when implemented correctly, BFR training appears to pose no more risk than traditional exercise (24).

However, widespread protocol inconsistencies within the literature raise questions about what constitutes “correct” application. This variation appears to have translated into variation among practitioners as well (27). To date, no consistent protocols have been established addressing tourniquet pressure, tourniquet width, repetition count, and ischemic time (27). The wide variability among studies raises concerns not only about safely applying BFR training principles, but also about possible variations in efficacy depending on the protocol chosen. Establishing safe and effective protocols to standardize use among practitioners is the next logical area of investigation.

AUTHOR’S PROTOCOL

The current authors have experience using BFR training in collegiate and international-level wrestlers and have previously described their protocol when using the KAATSU Nano system (KAATSU Global, Inc.) (28). The following outlines their current protocol using the third-generation tourniquet Delphi system from Owens Recovery Science (ORS) and is based on best-practice evidence in the literature.

The determination of individual limb occlusion pressure (LOP), or the pressure at which arterial flow into the extremity stops, is required to both safely and effectively use BFR training. Because the goal of BFR training is to impede vascular outflow, rather than complete arterial occlusion, the pressure at which this arterial occlusion occurs must be determined for each individual athlete. Variables such as cuff width, tourniquet pressure, and limb circumference all affect LOP. The Delphi system recommends a pressure resulting in an 80% occlusion for the lower extremities and 50% for upper extremities. These pressures are consistent with current literature, suggesting that LOP between 40% and 80% is safe and effective (29). However, these suggested pressures can be altered based on patient tolerance. Delphi is a personalized tourniquet pressure device using a built-in system to measure vascular flow. The Delphi system helps reduce the many variables such as cuff width, blood pressure, and limb size, which all can affect LOP calculations. The author’s protocol (Table) is based on the preestablished ORS protocol and the ORS user manual (30). BFR training sessions typically consist of 5 minutes of inflation and 1 minute of rest. Training frequency is recommended to be a minimum of 2 to 3 days a week with an intensity of 15% to 30% of the athlete’s 1RM (31). A wide variety of exercises can be used, depending on target area and muscle groups, and it is important to note that treatment protocols vary based on the level of athlete, age, injury, and/or surgery that has occurred.


TABLE -
Author’s BFR Training Protocol using the Third-Generation Tourniquet Delphi System from Owens Recovery Science (ORS)














1. A limb protection sleeve is placed on the patient and the tourniquet cuff is applied over top.
2. The LOP is then calculated while the patient is supine, and the limb is relaxed. The Personalized Tourniquet Pressure (PTP) button on the touch-screen machine initiates the LOP calculation. After LOP is calculated, Delphi will provide the PTP for the session.
3. Set 1, exercise 1: 30 repetitions, each consisting of a 2-second concentric contraction followed by a 2-second eccentric contraction. Weight is 20% to 30% of patient’s 1RM.
4. 30 seconds of rest with cuff inflated
5. Set 2, exercise 1: 15 repetitions
6. 30 seconds of rest with cuff inflated
7. Set 3, exercise 1: 15 repetitions
8. 30 seconds of rest with cuff inflated
9. Set 4, exercise 1: 15 repetitions
10. 1 minute of rest with cuff deflated
11. Repeat protocol with 2 to 3 more exercises

CONCLUSIONS

BFR training has shown benefit across diverse populations, from trained athletes to elderly populations. Current literature supports its potential utility in the prevention of disuse atrophy after acute or chronic injury, as well as the recovery of muscle strength more quickly during rehabilitation. The addition of low-load BFR training to traditional high-load resistance training also has the potential to augment strength and functional improvements in amateur and trained athletes alike. However, further research is necessary to determine optimal protocols for maximizing safety and results.

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