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Optimizing the use of blood flow restriction in strength training

by P. Debraux | 18 December 2024

Muscle strength and mass are essential. For athletes, they determine performance. For sedentary people in good health, for those with chronic illnesses or for the elderly, muscle strength and mass are positively correlated with life expectancy. To build muscle mass and increase strength, resistance training remains the best non-pharmacological intervention. Muscle gains are generally linked to training intensity, i.e. the relative load used. With relatively heavy loads (>80% 1RM), a superior effect on strength improvement is generally observed for gains in strength and hypertrophy compared to training with relatively light loads (30-60% 1RM). However, it's important to note that training with heavy loads can induce pain, injury or the onset of cardiovascular problems in populations suffering from chronic diseases, such as hypertension or osteoarthritis.

The best way to circumvent these limitations is to reduce the relative load used during training. In this case, it is necessary to adapt the number of repetitions to obtain significant effects on strength and muscle mass. For example, when training with a light load, it's best to train systematically to failure, doing as many repetitions as possible in each set. The disadvantage is that the duration of the sets, and therefore the total training time, will be significantly extended. Blood Flow Restriction (BFR) training, on the other hand, drastically reduces the number of repetitions required by inducing muscular hypoxia, thereby increasing the concentration of metabolites in the targeted muscle, leading to increased muscle fiber fatigue and, ultimately, recruitment of the larger motor units.

BFR combined with low-intensity strength training therefore appears to be a relatively safe alternative treatment to traditional training protocols for improving muscle and motor function in patients in clinical settings or in sedentary populations. However, despite its growing use in numerous studies and clinical settings, the absence of standardized criteria for BFR training protocols and equipment remains a problem. Indeed, to assess the effectiveness of BFR in improving muscle strength and hypertrophy, it is essential to better understand the impact of key parameters such as occlusion pressure, strap width and choice of resistance level.

The Study

To better understand the impact of different BFR protocols coupled with strength training on muscle strength and hypertrophy, Chinese researchers carried out a meta-analysis. They analyzed the results of 20 randomized controlled trials involving 28 intervention groups and a total of 515 young adults.

Studies were included if they met the following criteria: participants were healthy adults over 18 years old, the intervention involved strength training combined with BFR, a control group was present and did not receive treatment with BFR, and study outcomes focused on muscle hypertrophy (measurement of cross-sectional area or circumference) and muscle strength (measurement of 1RM or maximum voluntary isometric force).

Studies lasted between 3 and 14 weeks. The frequency of training sessions varied between 2 and 4 times a week, with only one study implementing a training frequency of 4 times a week.

With regard to the intensity of BFR combined with strength training, a range of 20% to 80% 1RM was observed among the intervention groups in the included studies. Twenty-three groups used intensities below 60% of 1RM, 2 used intensities of 60-80% of 1RM, and 3 an intensity of 80% of 1RM.

The intervention groups used different types of tourniquets. The length of these tourniquets was adapted to the cross-sectional area of the participants' arms or legs. In some studies, tourniquets of different widths were used. In addition, in 14 studies (20 intervention groups), tourniquets were inflated throughout training, and in 6 studies (8 intervention groups), tourniquets were inflated during exercise and deflated during rest periods.

Results & Analyzes

The main results of this study show that vascular occlusion ( BFR) combined with strength training produces results comparable to traditional strength training in terms of muscle strength and hypertrophy. Although medium- and high-intensity strength training is the most effective method for improving muscle strength and thickness, its application is sometimes limited in certain populations. Elderly people and hospitalized patients are often confronted with muscle weakness due to lack of exercise and/or loss of muscle mass. Although effective in improving muscle strength, weight training can present risks due to the acute hemodynamic response it triggers. Repeated elevation of arterial pressure increases endothelial shear and thrombin and fibrin concentrations, thereby increasing the risk of venous thrombosis. Resistance training with BFR, and with a light load, circumvents this problem and is often used in clinical contexts for functional rehabilitation.

With regard to load intensity, the results revealed no significant difference in improvements in muscle strength and thickness between low-intensity training with BFR (< 60% 1RM) and moderate- and high-intensity training with BFR (60-80% 1RM). Training with BFR at low load (30% of 1RM) has been shown to result in lower RPE scores than training at 70% of 1RM. For people lacking training experience or unable to withstand high-intensity training, implementing low-load training with BFR can alleviate discomfort during training. What's more, low-intensity resistance training with BFR places significantly less stress on joints, soft tissues and the cardiovascular system than high-intensity training.

In addition to training intensity, this meta-analysis explored the link between certain tourniquet characteristics and their effects on muscle hypertrophy. Tourniquet width and occlusion pressure are likely to influence the effectiveness of training protocols. Right now, there are no standardized criteria for tourniquet use. Previous research has suggested that larger tourniquets may exert greater occlusion pressure and thus induce more localized hypoxia, which could help stimulate muscle growth. And if we consider that a narrower cuff can lead to localized muscle damage due to increased tension, a wider cuff would be more practical and comfortable.

With regard to the pressure applied by tourniquets, the regression model highlighted that higher vascular occlusion correlated with more effective improvement in muscle hypertrophy. Nevertheless, careful occlusion selection is essential. Most studies have used an arterial occlusion pressure (AOP) of between 40% and 80%. It has been suggested that an AOP of 50% to 80% is optimal for training with BFR, and an AOP greater than 80% may increase the risk of adverse events during patient training, such as the potential induction of venous thrombosis.

Finally, no significant association between tourniquet deflation during rest periods and its impact on muscle hypertrophy was observed. However, the existing evidence may not be sufficient to establish a definitive relationship between tourniquet inflation status and the effects of BFR training on muscle hypertrophy. One study, for example, reported early discomfort and fatigue associated with inflated tourniquets during training, which could influence long-term muscle gains. The practice of deflating tourniquets during rest periods could help maintain adequate training volume for muscle hypertrophy.

Practical Applications

Low-intensity strength training with blood flow restriction is effective in improving strength and hypertrophy compared with a conventional training method. This meta-analysis suggests that program prescription could be guided by the following parameters: 2-3 training sessions per week at an intensity of 20-40% of 1RM. In addition, BFR can lead to discomfort and a reduction in total exercise volume. Careful attention to tourniquet width and occlusion pressure during procedures is essential to minimize potential adverse effects while achieving the desired muscle growth. It is therefore recommended to use a wider cuff and apply 50-80% of the arterial occlusion pressure during training. In addition, releasing the tourniquet pressure during rest periods would be beneficial in reducing discomfort.

And while this type of training may be less demanding for some patients, it can still impose some significant cardiovascular stress, which can lead to adverse effects. It is therefore important to consider the individual's state of health, and to check that there are no contraindications to the use of BFR.

References

  1. Ma F, He J and Wang Y. Blood flow restriction combined with resistance training on muscle strength and thickness improvement in young adults: a systematic review, metaanalysis, and meta-regression. Front Physiol 15:1379605, 2024.

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