Blood Flow Restriction — Benefits, Uses, & the Relationship Between Muscle Size and Strength

Understanding Muscle Fibers and Exercise

• Confusion surrounding muscle fiber identification methods 
  • Old methods vs. new methods
  • How fibers are classified as fast or slow
• Type 2x fibers: bigger, stronger, fatigue faster
• Type 2a fibers: more oxidative, forceful, can sustain for longer
• Type 1 fibers: slower, less forceful, resistant to fatigue
• Fiber type distribution may be influenced by genetics and training 
  • People often gravitate towards sports they’re good at
  • Genetic component likely plays a role in baseline fiber distribution
  • Training can improve certain aspects, but may not make someone elite

Strength and Hypertrophy

• Hypertrophy: increase in muscle fiber size 
  • Likely due to increases in overall protein, actin, and myosin
• Hyperplasia: increase in the number of muscle fibers 
  • Not thought to play a significant role in adults
• Strength improvements after training 
  • Can be broken down into mechanical strength and neurologic strength
  • Increase in one rep max and muscular endurance
  • Exact reasons for strength improvements not fully understood
    Neurological Changes and Strength
• Initial change in strength due to neurological changes 
  • Signal sent from the brain through the spinal cord to the alpha motor neuron (nerve that communicates with the muscle)
  • Changes could include more excitatory input, less inhibition, or lowered thresholds for firing type two fibers
• After 3–4 weeks, muscle size also contributes to change in strength

Blood Flow Restriction (BFR) Training

• Developed by Yoshiaki Sato 
  • Inspired by sensation felt while kneeling at a Buddhist ceremony, similar to heavy squats
  • Experimented with restricting blood flow in lower and upper body
• First study on BFR published in 1998 by Shinahara 
  • One leg performed exercise with BFR, the other without
  • Greater change in strength observed in the BFR leg
• BFR aims to reduce blood flow going into the limb, but not completely occlude it 
  • Early studies had variability in pressure applied
  • Current methods account for blood pressure, limb size, and cuff size

Katsu Training

• Japanese term meaning “increasing pressure”
• A brand of BFR training
• Should not be used as a generic term unless using Katsu apparatus
  Blood Flow Restriction (BFR) During Exercise
• BFR involves restricting blood flow during exercise using a cuff 
• The cuff is inflated to a percentage of the pressure at which blood flow is completely occluded
• Cuff size matters: wider cuffs require lower pressure to reach occlusion
• 40–80% of occlusive pressure is typically used in studies 
  • 40% is used for muscle adaptations (size and strength)
  • 80% may be used for vascular changes, but discomfort is higher
• Discomfort varies between individuals at the same occlusive pressure
• Blood flow restriction is not necessarily the same as the percentage of occlusive pressure applied
• BFR can be used during low-​​intensity aerobic exercise or resistance training 
  • For aerobic exercise, cuffs can be worn for 30–40 minutes
  • For resistance training, start with one exercise (four sets) and gradually increase to a few exercises
  • Cuffs should not be worn continuously for more than a few exercises during resistance training
    Blood Flow Restriction Training
• Start with 40% to 80% of occlusive pressure 
  • Can use Doppler or base pressure as a percentage of systolic blood pressure
  • Can also use percentage of resting limb size or conditioning to feel what 40% feels like
• Use weights around 20% to 40% of one rep max 
  • Lower loads (20%-30%) are generally preferred
• Pace: 1 second up, 1 second down (or 1.5 seconds)
• Rest: 30 seconds between sets 
  • Supersetting with different muscles can also be effective
• Can be used with compound movements, but isolation movements are generally safer and more effective for growth
• Risks: blood clotting and muscle damage 
  • No increased risk compared to high load exercise
  • No significant increase in CK levels or structural damage
• Blood pressure response: higher than without restriction, but comparable to high load exercise
  Blood Flow Restriction Training
• Comparing high load exercise to blood flow restriction training 
  • Blood pressure returns to baseline within 5 minutes in healthy individuals
  • Certain populations may hyper respond to blood flow restriction
• Relationship between strength and hypertrophy 
  • Conventional thinking: neural first, followed by muscle hypertrophy
  • Research shows muscle growth similar to high load exercise, but strength gains are less
  • Correlation between strength and size exists in both trained and untrained individuals
• Studies on muscle growth and strength 
  • Mortal and DeVries study: inferred muscle growth from changes in EMG amplitude 
    • One arm lifted weights, the other did not
    • Changes in EMG slope inferred as muscle growth; no change in slope considered neural
  • Questions remain on the causal relationship between muscle growth and strength gains
  • Blood flow restriction training may increase efficiency in fatiguing muscle fibers
  • Potential benefits of blood flow restriction beyond resistance exercise (e.g., vascular response)
    Hypertrophy and Strength Relationship
• Hypertrophy and strength relationship not fully understood 
• Landmark paper by Ikai and Fukunaga documented changes in muscle size in response to resistance exercise 
  • Assumed muscle growth changes contribute to strength
  • If no muscle growth change and strength increases, it’s neural
• Some studies suggest neural factors play a predominant role in exercise-​​induced changes
• Mediation analysis found no partial or complete mediation between muscle growth and strength 
  • Suggests muscle growth may not be a mechanism for strength increase
  • More research needed to conclusively rule out muscle growth as a mechanism

Practical Implications

• For maximal strength, focus on specificity and training close to one-​​rep max
• Muscle growth may play a small role, if any, in strength increase
• Allocating less time to muscle growth-​​focused training may benefit strength athletes
• More research needed to fully understand the relationship between hypertrophy and strength
  Local Changes in Muscle and Strength
• Possible local changes at the muscle level that might explain strength increase without muscle growth 
  • How muscle deals with calcium
  • How myosin head binds
• Neural component likely plays a significant role

Blood Flow Restriction (BFR) in Athletes

• Becoming more common in athletic departments and professional sports
• Used for rehab and recovery
• Some athletes use BFR for everyday training to recover faster

BFR in Bodybuilding

• Can be a valuable tool for hypertrophy
• Allows for personal preference in training
• Can be used on days when heavy lifting is not ideal or focus is lacking
• Provides variety in training
• Useful for rehabilitation

Super Slow Lifting Protocols

• Reasonable for those who don’t have the desire or technical skills for traditional training
• Likely not as beneficial as traditional training unless done to failure
• Difficult to truly fail in super slow workouts

Traditional Lifting for Maximum Strength

• Necessary for training maximum strength in exercises like bench press, squat, deadlift, and leg press
• BFR with low loads can increase strength, but to a much smaller degree than traditional exercise
• Practicing lifting heavy weight is the best way to get better at lifting heavy weight
  Blood Flow Restriction (BFR) Training
• Two areas where BFR shines: 
  1. Individuals who can’t lift heavy weights but need to get stronger and potentially bigger (e.g., recovering from injury or concerned about injury avoidance)
  2. Hypertrophy (muscle growth) — BFR can produce slightly superior hypertrophy response despite less total volume and lower load
• BFR is more efficient in generating hypertrophy compared to traditional exercise without BFR 
• Metabolites (e.g., lactate) pooling during BFR might augment muscle activation, causing the muscle to work harder and recruit more fibers, leading to growth 
• Mechanisms of BFR and traditional high-​​load exercise might be similar once muscle fibers are activated 
• Henneman’s size principle: type 1 motor units are recruited first, followed by type 2 motor units as needed based on exercise demands 
• Both type 1 and type 2 muscle fibers grow in response to high-​​load exercise and low-​​load exercise with BFR 
• Passive BFR (inflating and deflating without exercise) may slow muscle loss in injured individuals, but more research is needed 
• BFR can be used as a progression technique for individuals recovering from injury or surgery, transitioning from passive BFR to walking with BFR, and eventually to resistance exercise with BFR
  Blood Flow Restriction (BFR) and Muscle Loss
• Muscle loss occurs in sedentary individuals following elective surgery, emergent surgery, and injuries 
  • Disproportionately affects the elderly, leading to devastating effects
  • A year of hard training can be lost in just ten days of hospital bed rest
• BFR could potentially slow muscle loss 
  • Should be explored more in the elderly population
  • Could become standard of care if proven effective
• BFR progression: passive, low-​​end aerobic, low-​​load resistance, high-​​load resistance
• Large-​​scale studies needed to answer questions about BFR’s effectiveness

Strength and Overall Function

• Investigating the relationship between strength gained from resistance training and overall function 
  • How does increased strength affect walking ability and other functional aspects?
• Applying BFR to this area of research could provide valuable insights

Blood Flow Restriction (BFR) Research

• Current studies on BFR have small sample sizes
• Large-​​scale, long-​​term studies needed to answer questions about BFR’s effectiveness
• Research funding allocation should prioritize BFR and muscle loss prevention, especially in the elderly population