Blood Flow Restriction Article Summary
- The study’s results suggest that type I fiber hypertrophy is at least as great, and sometimes greater, than type II hypertrophy when performing low-load-blood flow restriction training (LL-BFR). This contrasts with high-load (HL) training, where type II fiber hypertrophy tends to be substantially greater than type I fibers.
- The review found that LL-BFR resistance training can be an effective alternative to traditional high-load resistance training for individuals unable or unwilling to lift heavy weights.
- The review’s authors conclude that while LL-BFR appears to be an effective strategy for targeting type I fiber hypertrophy, more research is needed to directly compare its effects with those of HL training protocols.
Are you looking for a novel approach to boost muscle growth and strength without using heavy weight? Look no further than Blood Flow Restriction Training (BFRT). This blog will dive deep into the science behind BFR and its contribution to Type I hypertrophy. This blog will take a deep dive into a new systematic review titled “Fiber-Type-Specific Hypertrophy with the Use of Low-Load Blood Flow Restriction Resistance Training: A Systematic Review” by Dr. Schoenfeld and colleagues. (Schoenfeld et al., 2023) The review has shed light on an alternative method that could revolutionize our understanding of strength training and muscle growth using low-load resistance training (i.e., light weights) in combination with blood flow restriction.
BFR for ACL and Immobilization Injuries
Resistance training has traditionally focused on high-load training or heavy weight (i.e., 60-80% of a 1-RM) for muscle hypertrophy. BFRT is a novel approach to resistance training that has gained attention for its potential to enhance muscle growth and strength gains. Incorporating BFR into physical therapy sessions can provide additional benefits for patients recovering from injuries or surgeries. Some physical therapists use blood flow restriction training to reduce muscle atrophy (i.e., muscle loss) after injuries such as ACL reconstruction and knee surgery.
What is Blood Flow Restriction Training, and How Does it Work to Increase Hypertrophy?
Blood flow occlusion is performed by applying a specialized blood pressure cuff, tourniquet, or strap proximal to the working muscle. BFRT partially restricts the blood flow, creating targeted metabolic stress through the use of BFR. This restriction results in a greater accumulation of metabolites and low oxygen availability, believed to enhance the stress on type I muscle fibers. (Ogborn & Schoenfeld, 2014) This low-load blood flow restriction training (LL-BFR) method stimulates Type I hypertrophy, a specific type of muscle growth usually associated with endurance activities.
How does BFR Affect Muscle Physiology
BFR occlusion works by occluding blood flow temporarily by compressing blood vessels, leading to the accumulation of metabolites such as lactic acid and an increase in growth hormone release. These metabolic changes activate protein synthesis, resulting in muscle fiber hypertrophy. (Loenneke et al., 2011) Additionally, cell swelling has been suggested as a mechanism for type I muscle hypertrophy with BFRT, as the restriction of blood flow leads to the accumulation of metabolites and fluid in the muscle cells, resulting in cell swelling and muscle growth (Loenneke et al., 2011).
The Role of BFR, Fatigue, Motor Unit Recruitment, and Satellite Cells
BFRT has been shown to increase motor unit recruitment (i.e., activation of type I and type II muscle fibers) during exercise. When BFR is applied to the limbs, it restricts blood flow to the muscles, leading to a decrease in oxygen supply and an accumulation of metabolites. This creates a lack of oxygen to muscles and metabolically stressful environment, which stimulates the recruitment of muscle fibers.
Previous studies have found BFRT can stimulate muscle fiber recruitment similar to heavy weight training. Henneman et al., demonstrated that the recruitment of skeletal muscle fibers follows the size principle. According to this principle, low-threshold motor units (associated with the type I fibers) are activated first, with higher-threshold motor units (associated with the type II fibers) progressively recruited thereafter to meet force demands.(Henneman et al., 1965)
LL-BFR (low-load blood flow restriction) training, also known as low-intensity resistance training, has been shown to potentially increase type I fibers. (Grgic & Schoenfeld, 2018) The stress response to LL-BFR is more pronounced in type I fibers than in type II fibers, which may result in greater hypertrophy of slow-twitch fibers. In this regard, LL-BFR may induce a greater stimulus to the fatigue-resistant type I fibers, given that such training involves an extended time under-tension. (Martineau & Gardiner, 2002) Finally, LL-BFR may increase the activation of satellite cells involved in muscle repair and growth. (Takarada et al., 2002)
The Benefits of Blood Flow Restriction Training on Type I Muscle Fibers
Type I muscle fibers, known as slow-twitch fibers, are typically associated with endurance activities. They are more fatigue-resistant and have a slower contraction speed than type II fibers, which are fast-twitch and more suited for power and speed activities.
Specifically, high-repetition, light weight lifting targets type I fibers, while low-repetition, heavy weight (or sometimes high velocity) training targets type II fibers.(Jozo Grgic et al., 2018) For power athletes, type II fiber-specific hypertrophy is attractive, while bodybuilders are interested in the potential of using both high- and low loads to synergistically maximize total muscle growth of both type I and II fibers.
A bodybuilder looking to increase muscle size may be interested in using compression therapy because it preferentially increases type I fibers, which are normally only increased with aerobic exercise. Increasing both type I and II fibers will result in an overall greater increase in muscle size.
What Does Blood Flow Restriction Training Do to Type I Fibers?
Interestingly, LL-BFR could lead to a similar, if not greater, hypertrophy of type I fibers compared to regular strength training. This is a significant finding, as heavy weight training typically results in greater hypertrophy of type II fibers. Athletes participating in muscular endurance sports would benefit the most from BFRT.
Additionally, bodybuilders looking to increase muscle size would benefit from BFRT as it can increase both type I and type II fibers, resulting in overall greater size. Furthermore, some studies have suggested that BFR may be particularly beneficial for athletes who are recovering from injuries or who are unable to perform high-intensity exercise due to other factors (e.g., age, joint pain)(Cook et al., 2007)
Does Blood Flow Restriction Training Work? Results from New Review
A new study published in the Journal of Functional Morphology and Kinesiology aimed to systematically review the effects of low-load blood flow restriction (LL-BFR) resistance exercise on fiber-type-specific hypertrophy.
The researchers analyzed various studies that investigated the longitudinal effects of LL-BFR on muscle fiber size and compared it to high-load (HL) resistance exercise. The review included 11 studies that met the inclusion criteria. The study duration ranged from 2 to 9 weeks. Intensities of load ranged from 20% 1RM to 50% 1RM in the LL-BFR condition. All studies solely measured muscle growth of the vastus lateralis muscle.
The review found that LL-BFR can lead to significant increases in muscle size, particularly in type I fibers, and that the magnitude of type I fiber hypertrophy is at least as great, and sometimes greater, than type II hypertrophy when performing LL-BFR. However, the overall findings were mixed, with some studies showing similar hypertrophic responses between LL-BFR and HL exercise.
The effects of LL-BFR on type I fiber cross-sectional area appear to be more pronounced with frequent exercise bouts (>5 days/week). However, some studies show a preferential effect on type I fibers with lower exercise frequencies. The authors also note that current research has almost exclusively involved younger participants. Given the greater percentage of type I fibers in older muscles, it is conceivable that LL-BFR might promote greater overall hypertrophy with advancing age. However, further research is needed to confirm this hypothesis.
Is Blood Flow Restriction Training Safe?
As for the risks, it is important to note that LL-BFR should be performed under proper supervision and guidance to ensure safety. Improper use of blood flow restriction could lead to complications such as blood clots, nerve damage, or muscle damage. Following appropriate protocols and guidelines is crucial when implementing LL-BFR in resistance exercises. Additionally, LL-BFR may not be appropriate for individuals with certain medical conditions, such as hypertension, deep vein thrombosis, or peripheral artery disease. It is important to consult with a qualified healthcare professional before beginning the LL-BFR exercise to determine if it is safe and appropriate for your needs and goals.
Practical Implications of Blood Flow Restriction Training
For those unfamiliar with these two concepts, BFR is resistance exercise for the limbs with low loads (20-50% 1RM) while restricting blood flow proximally (at the groin or armpit) with a cuff or wrap. (J. Grgic et al., 2018) You use tightness sufficient to maintain arterial inflow while restricting venous outflow, subjectively prescribed at a 7 out of 10 tightness or objectively to a specific mmHg blood pressure value. (Grgic et al., 2020)
Researchers are still exploring BFRT bands and the benefits of blood flow restriction exercise. Although the current research shows promise, we need to do more to fully comprehend this training method’s potential. So, does blood flow restriction exercise yield results? Yes, it does, but we need more studies to fully grasp its potential and determine the best way to utilize it.
The practical implications of blood flow restriction BFRT include the potential to achieve similar muscle hypertrophy and strength gains with lower-weight exercise, which may benefit individuals unable to tolerate high-intensity exercise due to fatigue, joint pain, or other factors. BFRT may also be useful for individuals recovering from injury or surgery, as it can help maintain muscle mass and strength during periods of immobilization.
Cook, S. B., Clark, B. C., & Ploutz-Snyder, L. L. (2007). Effects of exercise load and blood-flow restriction on skeletal muscle function. Med Sci Sports Exerc, 39(10), 1708-1713. https://doi.org/10.1249/mss.0b013e31812383d6
Grgic, J., Garofolini, A., Orazem, J., Sabol, F., Schoenfeld, B. J., & Pedisic, Z. (2020). Effects of Resistance Training on Muscle Size and Strength in Very Elderly Adults: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Sports Medicine, 50(11), 1983-1999. https://doi.org/10.1007/s40279-020-01331-7
Grgic, J., Homolak, J., Mikulic, P., Botella, J., & Schoenfeld, B. J. (2018). Inducing Hypertrophic Effects of Type I Skeletal Muscle Fibers: A Hypothetical Role of Time Under Load in Resistance Training Aimed at Muscular Hypertrophy. Medical Hypotheses. https://doi.org/10.1016/j.mehy.2018.01.012
Grgic, J., & Schoenfeld, B. J. (2018). Are the Hypertrophic Adaptations to High and Low-Load Resistance Training Muscle Fiber Type Specific? [Opinion]. Frontiers in Physiology, 9. https://doi.org/10.3389/fphys.2018.00402
Grgic, J., Schoenfeld, B. J., Skrepnik, M., Davies, T. B., & Mikulic, P. (2018). Effects of Rest Interval Duration in Resistance Training on Measures of Muscular Strength: A Systematic Review. Sports Med, 48(1), 137-151. https://doi.org/10.1007/s40279-017-0788-x
Henneman, E., Somjen, G., & Carpenter, D. O. (1965). FUNCTIONAL SIGNIFICANCE OF CELL SIZE IN SPINAL MOTONEURONS. Journal of Neurophysiology, 28(3), 560-580. https://doi.org/10.1152/jn.19126.96.36.1990
Loenneke, J. P., Wilson, J. M., Marín, P. J., Zourdos, M. C., & Bemben, M. G. (2011). Low Intensity Blood Flow Restriction Training: A Meta-Analysis. European Journal of Applied Physiology. https://doi.org/10.1007/s00421-011-2167-x
Martineau, L. C., & Gardiner, P. F. (2002). Skeletal muscle is sensitive to the tension-time integral but not to the rate of change of tension, as assessed by mechanically induced signaling. J Biomech, 35(5), 657-663. https://doi.org/10.1016/s0021-9290(01)00249-4
Ogborn, D., & Schoenfeld, B. J. (2014). The Role of Fiber Types in Muscle Hypertrophy: Implications for Loading Strategies. Strength & Conditioning Journal, 36(2). https://journals.lww.com/nsca-scj/Fulltext/2014/04000/The_Role_of_Fiber_Types_in_Muscle_Hypertrophy_.3.aspx
Schoenfeld, B. J., Ogborn, D., Piñero, A., Burke, R., Coleman, M., & Rolnick, N. (2023). Fiber-Type-Specific Hypertrophy with the Use of Low-Load Blood Flow Restriction Resistance Training: A Systematic Review. J Funct Morphol Kinesiol, 8(2). https://doi.org/10.3390/jfmk8020051
Takarada, Y., Sato, Y., & Ishii, N. (2002). Effects of resistance exercise combined with vascular occlusion on muscle function in athletes. Eur J Appl Physiol, 86(4), 308-314. https://doi.org/10.1007/s00421-001-0561-5
Is Blood Flow Restriction Training Safe?
Blood Flow Restriction Training can be safe if done correctly and supervised by a professional. It’s crucial to use the right equipment and technique. People with medical conditions should consult a healthcare professional first. Gradually increasing intensity and duration helps minimize the risk of injury.
Practical Implications of Blood Flow Restriction Training
The choice of cuff material greatly impacts the comfort and effectiveness of BFR training. Nylon cuffs, known for their affordability, may be less comfortable for prolonged use. On the other hand, rubber cuffs strike a balance between comfort and durability.
BFR Cuff Pressure
BFR cuff pressure is a crucial factor that significantly influences the outcomes of blood flow restriction training. This, in turn, contributes to the desired muscle growth and hypertrophy.