Blood Flow Resistance (BFR) training is gaining more traction in research and practical application. I talked about BFR nearly five years ago. Since then, others have done different types of blood flow restriction for many years (like KAATSU). However, research is still being done to determine the effectiveness and best protocols for BFR.
Luckily, we have Luke Hughes, a leading researcher, join us to discuss BFR training and their current research. He graduated from Loughborough University with a BSc (Hons) in Sport and Exercise Science. After graduating he did an MSc in Exercise Physiology at Loughborough, specialising in Exercise Immunology.
Luke now studies at St Mary’s as a PhD student in Exercise Physiology. He is based between St Mary’s and University College Hospital London, at the ISEH, where he is an honorary researcher.
Luke teaches physiology and research methods on undergraduate degrees within the School of Sport, Health and Applied Science, and has also taught exercise immunology on the MSc Strength and Conditioning. He also teaches Anatomy and Physiology as part of the ITEC Sports Massage short courses at St Mary’s University.
Luke’s research is focused on the use of blood flow restriction training in clinical musculoskeletal rehabilitation and neuromuscular electrical stimulation with blood flow restriction.
What is Blood Flow Resistance Training
“Blood flow restriction training, also referred to as occlusion training, involves restriction of blood flow during exercise. It is typically applied during low-load exercise, achieved using pneumatic or non-pneumatic tourniquets, and aims to partially restrict arterial inflow to the muscle and occlude venous return. This results in an ischemic and hypoxic muscular environment distal to the cuff, and blood pools within the working muscles, along with extensive exercise-induced metabolite accumulation due to constrained venous removal.
In terms of subjective responses, research has shown that perceived exertion and pain is higher during acute low-load BFR exercise compared with low-load exercise without BFR (both 30% 1RM). However, such reported values for perceived exertion and pain are not necessarily high, and comparison of perceptual responses to low-load BFR (30% 1RM) versus heavy load (70% 1RM) exercise demonstrates that these responses are lower in low-load BFR exercise compared with an equivalent form of exercise at a higher intensity. Finally, research has demonstrated a similar time course of adaptation to perceptual responses between low-load BFR and heavy-load exercise.”
Why are Many People Interested with BFR Training
Many people are interested in the application of BFR for building muscle (hypertrophy) and strength. They say:
“Blood flow restriction is typically applied during low-load/intensity exercise to produce muscular adaptations that are not commonly achieved using low-loads/intensities alone. Augmentation of low-load resistance training with blood flow restriction has been shown to elicit greater muscle hypertrophy responses compared to low-load training alone, with loads as low at 20% 1RM.[2, 3] In addition, BFR has been found to yield hypertrophy responses comparable to that observed with heavy-load resistance training, suggesting low-load BFR training may provide a surrogate for heavy-load training in contraindicated populations. However, at present such findings are not common. That aside, the hypertrophic capacity of low-load resistance training with BFR is well documented.”
Low-Load Training with BFR
Low-load resistance training with BFR has also been shown to produce significant increases in muscle strength.[3, 5-6] Strength increases and hypertrophy have also been observed with aerobic BFR training, including cycling and slow walk training, thus low-intensity aerobic training may be used to stimulate muscle hypertrophy and increases in strength when low-load resistance training may not be applicable, i.e. early post-surgery. Such increases are not commonly observed with an aerobic form of exercise; thus, the ischemic and hypoxic environment is the likely trigger of muscular adaptations.
Although there is a vast amount of research demonstrating the strength gain and hypertrophic capacity of BFR training, the mechanism by which hypertrophy is achieved has not been pragmatically identified. Metabolic stress and mechanical tension have been described as primary hypertrophy factors for muscle growth, and theorized to activate other mechanisms for the induction of muscle growth in low-load BFR training. These include: elevated systemic hormone production, cell swelling, increased fast twitch fibre recruitment and intramuscular anabolic/anti-catabolic signaling. However, at present these are mainly hypothetical and theoretical-based associations. When comparing low-load BFR training to heavy load training there appears to be similarity in terms of molecular factors that lead to muscle growth. Strength gains may be driven by hypertrophy and neural adaptations similar to those observed with heavy-load training, and the underlying mechanisms are also likely similar. However, with BFR exercise, these mechanisms may be activated by the combination of tension and hypoxia.”
Many people automatically jump to performance, but rehabilitation is also an area where BFR may be helpful.
BFR Training as Rehabilitation Tool
“Although BFR training was initially used in healthy and athletic populations, the low-load nature and hypertrophic capacity of BFR training makes it an attractive rehabilitation tool for clinical populations where heavy loads required to stimulate hypertrophy and strength adaptations are not feasible/dangerous. Such populations include; fractures and ligament injuries, osteoarthritis, sarcopenia, myositis and other musculoskeletal [MSK] conditions/injuries requiring surgery. Low-loads are commonly used during early rehabilitation; our recent systematic review and meta-analysis found low-load BFR training was more effective at increasing muscle strength compared to low-load training alone, and is likely also more effective for stimulating hypertrophy. We also concluded that, at present, heavy-load training is more effective at increasing strength; therefore, BFR training should be used as a clinical MSK rehab tool in a progressive manner, from early ambulation to return to heavy-load exercise. A progressive model of BFR application has been proposed, where BFR is used during bed rest, then in combination with low-load aerobic training then low-load resistance training, until the individual can return to heavy-load exercise.
Implementation of BFR Training
BFR training has been reviewed in depth; it has been concluded that correct implementation presents no greater risk than traditional exercise. An epidemiological study reported low occurrence of adverse events other than skin bruising. However, concerns over disturbed hemodynamics, ischemic reperfusion injury and rhabdomyolosis still exist. Moreover, incorrect implementation and screening prior to implementation may increase the risk of such adverse events occurring. It is important to properly screen for any blood disorders, hypertensiveness, and previous MSK injuries before using BFR, and rule out potential causes of rhabdomyolosis, such as infections and prolonged immobilisation. Additionally, when using BFR in post-surgery rehabilitation, it is important to consider the degree of swelling around the injured joint/muscle/bone before using BFR, given that BFR has been shown to cause swelling. Finally, including measures of muscle damage markers (e.g., serum creatine kinase) throughout the rehabilitation training period is important to monitor the physiological response to BFR.”
What Are Safety Recommendations in BFR Training
To ensure safety, experts proposed:
“The recent systematic review and meta-analysis from our group analysed the quality and reporting of exercise training studies that have used BFR as a clinical rehabilitation tool. The results indicated that many of the studies were not individualizing the occlusive stimulus and training load, and not assessing the risk of adverse events to BFR. Furthermore, in a questionnaire study produced by our group we identified that practitioners are not always following the current recommendations in the literature. Despite the use of low loads, prolonged training studies greater than two weeks in duration should reassess training load to ensure individuals are still training at 20/30% of their 1RM – given the strength gains that have been reported with BFR – to ensure continued progression. Moreover, the occlusive stimulus should be prescribed on an individual basis to ensure that an effective stimulus is being applied. Thigh circumference is a determinant of the pressure required to restrict blood flow, thus different pressures are needed in different individuals to reach the same level of occlusion. Calculation of limb arterial occlusive pressure [LOP] allows for selection of a pressure at a percentage of LOP – at present, 80% LOP is common among the emerging clinical BFR literature, but some research has also shown that higher LOP pressures are not required for greater facilitation of muscular responses to exercise compared with lower pressures. For example, 40% LOP produced similar increases in muscle size, strength and endurance after 8 weeks of training to that of 90% LOP but without the high ratings of discomfort that were reported with the latter pressure.
At present, we recommend using a pressure between 40-80% LOP during blood flow restriction exercise, with the cuff remaining inflated during rest periods to allow for metabolite accumulation within the muscle. Regarding repetitions and sets, 4 sets to failure or 4 sets (30, 15, 15, 15 reps) appears to be the most effective. Although BFR exercise is safe if implemented correctly, we recommend that total occlusion time does not exceed 10 minutes to avoid the risk of excessive muscle damage.”
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