Blood Flow Restriction (BFR ) Exercise Part II: Enhancing Strength, Hypertrophy, and Power

Blood Flow Restriction (BFR) Can Optimize strength, endurance, motor control, and power whether an individual is focusing on recovering from an injury or training to enhance sports performance. 

By Dr. John R. Mishock, PT, DPT, DC






In Part I of Blood Flow Restriction (BFR), we reviewed the history of the technique and the evidence of its use during physical therapy and rehabilitation when returning from injury or orthopedic surgery ( Whether an individual is focusing on recovering from an injury or training to enhance sports performance, BFR can optimize strength, endurance, motor control, and power. In this article, I will review the physiological mechanisms behind BFR.

How do we gain muscle hypertrophy and strength?

Muscle hypertrophy and strength happen when there is significant (70-90% 1 repetition maximum) mechanical and metabolic stress during exercise. The mechanical tension causes muscle damage (increases muscle growth) and hormone production (Testosterone, growth hormone). Metabolic stress is the cell’s build-up of metabolites (reactive oxygen species, hydrogen ion, phosphate, and lactate) and swelling. The mechanical and metabolic stress increases the use of fast-twitch muscle while increasing protein synthesis (muscle building), lending to hypertrophy and strength. One of the most common errors in training is not using enough resistance or weight (70-90% of 1 RM) in exercise training when the goal is to gain strength and hypertrophy.

What is the difference between muscle strength and muscle power? 

Muscle strength is the amount of force an individual can develop, either isometric (muscle contraction with no joint movement), concentric (muscle contraction reducing the joint angle), or eccentric (muscle contraction lengthening the joint angle). From a physics perspective, an athlete uses his strength to produce a force on himself or an object (bat, ball, ground, person…) causing movement. The movement is defined as work (force x distance). If that work occurs rapidly (rate of force development) over a brief period, it is called power (force x distance/time). (Samozineo et al. 2012) Simply put, when you have strong muscles contract fast, you get power. The power allows the athlete to optimize jumping, sprinting, change-of-direction, throwing, and hitting. High amounts of fast-twitch type II muscle (fast-twitch type IIa to type IIb) are critical to high force development and power. Fast-twitch type IIa is used to move a semi-heavy object. Fast-twitch type IIb or X is the largest fiber type used in all-out muscular effort (jumping, sprinting, throwing hard). Creating large amounts of type IIb muscle is the goal for athletes in explosive sports (basketball, baseball, football, soccer, lacrosse). Muscle type is based on genetics; however, some fast-twitch type IIa can be changed to fast-twitch type IIb through certain types of training. (Cronin et al. 2005)

How does BFR help to increase muscle hypertrophy and strength?

BFR exercise causes the build-up of venous blood while maintaining arterial blood flow to the muscle. This physiological mechanism tricks the body into creating muscle hypertrophy and strength with lower loads of 1 rep max. In other words, you can use less weight and get an equal or greater training effect.

With BFR, how does restricting the venous return of blood increase muscle hypertrophy and strength, similar to high-load resistance training?  

BFR enhances muscle physiology in 7 ways.

  1. Exercise-induced metabolic stress: When a muscle contract, it uses glucose, fat, or protein as energy. The byproducts of that metabolism (hydrogen ion, phosphate, and lactate) accumulate in the muscle. The metabolite build-up inhibits slow twitch muscle, preferentially recruiting fast twitch muscle, similar to high-load resistance training. (Suga et al. 2010, Yasuda et al 2010, Karabulut et al 2014) Fast twitch muscle training is essential to gain strength, hypertrophy, and explosive power.
  2. Anabolic hormones: There is the acute release of anabolic hormones (Testosterone, growth hormone (GH), and insulin-like growth factor-1). These hormones are essential to increase muscle mass. These hormones are also released with high-resistance training.
  3. Increased protein synthesis: Our bodies are in a constant turnover of muscle breakdown and building (1.2% turnover per day). After working out, protein synthesis increases by 3-5 times for 48 hours (activation of MTOR and inhibition of myostatin). (Fry et al. 2010) BFR exercise at 20% of 1 rep max increases muscle protein synthesis by 56%. (Laurentino et al. 2012)
  4. Muscle swelling: BFR causes cellular swelling, further enhancing protein synthesis. (Loenneke et al. 2012)
  5. Increased ATP (Adenosine Triphosphate): ATP is the primary energy unit for the muscle. BFR increases ATP, allowing greater utilization of fast-twitch muscle. The lactate then goes to the bloodstream to the liver, where lactate is converted into pyruvate and then to glucose. The glucose goes back to the muscle for energy. (Fry et al 2010)
  6. Reduced muscle oxygenation (Cori cycle): BFR causes reduced oxygen to the muscle, stimulating fast-twitch muscle utilization instead of slow-twitch muscle, which uses oxygen. The reduced oxygen causes a lower PH in the muscle (increased hydrogen), which causes the release of lactate, which increases fast-twitch muscle activity (increased EMG and anaerobic metabolism). The lactate is turned back into glucose for energy in the liver. (Gamber et al. 2011)
  7. Hennamens size principle: The Hennamen size principle states that slow-twitch muscle fibers (smaller fibers) are used first when the resistance is low. As the resistance increases, more muscle fibers are utilized, with fast-twitch (Type II A, B, and X) being utilized with the greatest effort. BFR causes greater muscle fiber utilization at lower loads. (Garber et al. 2011)

In part III of Blood Flow Restriction (BFR) I will review how BFR can be used in healthy athletes to improve explosive power and athleticism to enhance sports performance.

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Dr. Mishock is one of only a few clinicians with doctorate-level degrees in both physical therapy and chiropractic in the state of Pennsylvania. He has authored two books; “Fundamental Training Principles: Essential Knowledge for Building the Elite Athlete”, “The Rubber Arm; Using Science to Increase Pitch Control, Improve Velocity, and Prevent Elbow and Shoulder Injury,” both can be bought on Amazon.

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