#179 - Jeremy Loenneke, Ph.D.: The science of blood flow restriction—benefits, uses, and what it teaches us about the relationship between muscle size and strength
Jeremy Loenneke, Ph.D., discusses Blood Flow Restriction (BFR) training, explaining its science, mechanisms for hypertrophy with low loads, and practical applications. He also delves into muscle physiology and challenges the conventional understanding of the relationship between muscle size and strength.
Deep Dive Analysis
14 Topic Outline
Jeremy Loenneke's Journey into Exercise Science
Understanding Muscle Microstructure and Physiology
Distinguishing Fast-Twitch and Slow-Twitch Muscle Fibers
Defining Muscle Hypertrophy and Strength
Origins of Blood Flow Restriction (BFR) Training
Methods for Applying and Calibrating BFR Pressure
Practical Considerations for BFR Exercise
Safety Profile and Risks of BFR Training
Rethinking the Relationship Between Muscle Size and Strength
BFR Applications for Athletes and General Population
Optimal Scenarios for BFR Training
Mechanisms of BFR-Induced Hypertrophy at Low Loads
Potential Benefits of Passive BFR Training
Future Research in Strength and BFR
9 Key Concepts
Sarcomere
The smallest functional unit of a muscle, composed of actin and myosin proteins that interact to cause muscle contraction. When a muscle grows, it's primarily due to synthesizing more of these proteins.
Actin and Myosin
These are the primary proteins within a sarcomere. Myosin interacts with actin, pulling it to contract the muscle. ATP is specifically required to break the bond between actin and myosin, allowing for relaxation and re-cocking for subsequent contractions.
Type I (Slow-Twitch) Muscle Fibers
These muscle fibers are more endurance-based, less forceful, and highly resistant to fatigue due to their oxidative metabolism. They are generally smaller in size.
Type II (Fast-Twitch) Muscle Fibers
These muscle fibers are more force-based, stronger, and fatigue much faster. Type IIX fibers are typically the biggest and strongest but fatigue quickest, while Type IIA are more oxidative and can sustain force longer.
Hypertrophy
An increase in the size of individual muscle cells, primarily due to an increase in the amount of contractile proteins like actin and myosin. This is the main way adult muscles get bigger in response to exercise, rather than an increase in cell number (hyperplasia).
Strength (Neurological Component)
The initial rapid gains in strength when starting exercise are largely attributed to neurological adaptations. These include increased excitatory input from the brain, reduced inhibition, and lower thresholds for firing motor units, making it easier to activate muscle fibers.
Blood Flow Restriction (BFR)
A training technique that involves applying a cuff to a limb to reduce, but not completely occlude, arterial blood flow during exercise. This allows individuals to achieve hypertrophy and strength gains using much lower weights than traditional training.
Arterial Occlusion Pressure (AOP)
The lowest pressure at which there is no blood flow into a limb, typically measured with a Doppler probe. It serves as a personalized reference point for setting BFR cuff pressures, ensuring consistent relative restriction across individuals.
Henneman Size Principle
This principle describes the order of motor unit recruitment during muscle contraction, stating that smaller, slower (Type I) motor units are recruited first, followed by larger, faster (Type II) motor units as the force requirement or fatigue increases.
12 Questions Answered
Muscle contraction occurs when actin and myosin proteins within the sarcomere slide past each other. A neural signal releases calcium, exposing binding sites, and myosin heads attach to actin, pulling them inward. ATP is then required to release this bond, allowing the cycle to repeat.
Slow-twitch (Type I) fibers are endurance-based, less forceful, and fatigue slowly, while fast-twitch (Type II) fibers are more force-based, stronger, and fatigue quickly. Type IIX are the most powerful but least enduring, with Type IIA being an intermediate type.
While training can shift fiber types along a continuum (e.g., Type IIX to Type IIA), there appears to be a significant genetic component to an individual's baseline fiber distribution, influencing their natural aptitude for certain athletic endeavors.
Hypertrophy refers to the increase in the size of individual muscle cells, primarily due to more contractile proteins. Strength is the ability to exert force, which can increase due to neurological adaptations (better muscle activation) and potentially local changes within the muscle, not necessarily solely from increased size.
BFR training, also known as Kaatsu, was developed by Dr. Yoshiaki Sato in Japan. He conceived the idea after experiencing numbness in his calves while kneeling at a Buddhist ceremony, which felt similar to the sensation of heavy squats, leading him to experiment with restricting blood flow.
BFR aims to reduce arterial blood flow without complete occlusion. In research, this is typically achieved by first measuring the Arterial Occlusion Pressure (AOP) using a Doppler probe, then applying a percentage (e.g., 40-80%) of that pressure with a cuff, ensuring blood flow is maintained.
For muscle size and strength adaptations, a moderate pressure of around 40% of Arterial Occlusion Pressure (AOP) is typically used in research. Higher pressures (e.g., 80-90% AOP) can also produce similar muscle adaptations but result in significantly higher discomfort.
The safety profile of BFR is generally comparable to traditional high-load exercise. Concerns about blood clots and muscle damage have been studied, and BFR does not appear to increase the risk of either in healthy individuals when done appropriately. Blood pressure response is usually similar to or slightly lower than high-load exercise.
While muscle size and strength are correlated, current evidence suggests that muscle growth (hypertrophy) may not be a primary mechanism for increases in strength. Studies have shown similar strength gains in groups with and without muscle growth, and statistical mediation analyses often fail to show a causal link.
BFR training with low loads can produce similar or even superior muscle hypertrophy compared to traditional high-load training, often with less total volume and in a more time-efficient manner. However, for maximal strength gains, traditional high-load exercise remains superior, as it specifically trains the ability to lift heavy weights.
BFR-induced hypertrophy at low loads is thought to be driven by the trapping of metabolites (like lactate), which augments muscle activation. This metabolic stress causes earlier fatigue, leading to the recruitment of more muscle fibers, including fast-twitch fibers, for a sufficient duration to stimulate growth, similar to high-load training.
Passive BFR, where cuffs are applied without exercise, has shown promise in slowing muscle loss in highly injured or post-surgical individuals who cannot actively train. This could be a crucial tool for attenuating muscle atrophy, especially in elderly populations where muscle loss has significant morbidity and mortality implications.
24 Actionable Insights
1. Use BFR for Efficient Hypertrophy
Blood flow restriction (BFR) training with low loads is a more efficient method for generating muscle hypertrophy compared to work-matched low-load training without BFR, often yielding better results with less total volume and time.
2. Progressive BFR Rehab Protocol
For rehabilitation, progress BFR usage from passive application (if unable to move) to low-intensity aerobic exercise, then to low-load resistance training, and finally to high-load exercise if appropriate, to maximize recovery and adaptation.
3. Restrict, Not Occlude, Blood Flow
When using blood flow restriction, ensure that blood flow is reduced but not completely occluded, as the goal is to always have some arterial flow into the limb for safety and efficacy.
4. Determine Individual Occlusive Pressure
Before applying BFR, measure your arterial occlusion pressure (AOP) using a handheld Doppler probe to find the lowest pressure at which there is no blood flow, then use a percentage of that pressure for training to ensure appropriate restriction.
5. Moderate BFR Pressure for Growth
For muscle adaptations (size and strength), aim for approximately 40% of your arterial occlusion pressure (AOP), as it provides similar benefits to higher pressures (80-90% AOP) with significantly less discomfort.
6. Train with Low Loads in BFR
Utilize very low loads, typically around 20-30% of your one-repetition maximum (1RM), when performing blood flow restriction exercise to leverage its primary utility and achieve desired adaptations.
7. Gauge BFR Tightness by Reps
When using BFR with low loads (e.g., 20-30% 1RM), aim for around 30 repetitions on the first set and 15 on subsequent sets; if you cannot achieve these targets, the load is too high or the wraps are too tight.
8. Adjust BFR if Painful
If you experience pain before starting BFR exercise, your wraps are likely too tight and should be loosened to prevent excessive discomfort and potential issues.
9. Start BFR with One Exercise
When first incorporating resistance training with BFR, limit continuous cuff application to one exercise (around 7-10 minutes) to allow your body to adapt to the sensation and demands.
10. Limit BFR to Minutes
Remember that BFR involves restricting blood flow for minutes, not hours, which is a key factor in maintaining its safety profile.
11. BFR is Generally Safe
Blood flow restriction training has a safety profile comparable to traditional high-load exercise, as it does not appear to increase the risk of blood clots or muscle damage, and blood pressure responses are similar or lower than heavy lifting.
12. Prioritize Heavy Lifting for Strength
If your primary goal is to maximize strength in a specific lift, consistently training at or close to your one-repetition maximum (1RM) with heavy weights is the most effective method.
13. Avoid BFR with High Loads
Do not combine blood flow restriction with high load training, as it does not provide additional benefits beyond what high load exercise already offers and is likely a maximal stimulus on its own.
14. Metabolite Pooling Drives BFR Growth
BFR traps metabolites (like lactate), which augments muscle activation and induces fatigue, thereby recruiting more muscle fibers for a sufficient duration to stimulate muscle growth.
15. Supersetting with BFR is Effective
Supersetting can be effective with BFR, particularly when working a muscle not directly under restriction (e.g., chest exercises with BFR on arms), as the distal muscles fatigue and the chest picks up the load.
16. BFR for Training Variety
Implement BFR as a versatile tool on days when you lack focus or feel unable to lift heavy, as it allows for effective training with light weights and provides variety to your routine.
17. Account for BFR Cuff Size
Be aware that cuff size significantly impacts the pressure needed for occlusion; wider cuffs require lower pressure, so always measure AOP with the specific cuff you plan to use.
18. Maintain Controlled BFR Pace
When performing BFR exercises, use a controlled pace, such as one second for the concentric phase and one second for the eccentric phase, as speed does not significantly impact growth.
19. Use Short BFR Rest Periods
For resistance exercise with BFR, a standard rest period of approximately 30 seconds between sets is generally used to maintain metabolic stress.
20. Passive BFR Slows Muscle Loss
For individuals who cannot exercise (e.g., post-surgery), passive BFR (applying and deflating cuffs without exercise) may help slow down muscle loss, though more large-scale studies are needed.
21. BFR for Low-Intensity Aerobics
For low-intensity aerobic exercise, BFR cuffs can be kept on for 30-40 minutes, as the lower intensity makes it less discomforting and potentially beneficial for adaptation.
22. Higher BFR for Vascular Changes
Preliminary data suggests that achieving vascular changes, such as improvements in limb blood flow or conductance, might require higher BFR pressures (e.g., 80-90% AOP) compared to muscle adaptation.
23. Caution with Complex BFR Lifts
While multi-joint movements like squats or bench press can be done with BFR using lightweight, isolation movements are generally preferred for safety and targeted growth, to avoid altering mechanics and increasing injury risk.
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7 Key Quotes
ATP is required to break that bond.
Jeremy Loenneke
The idea of blood flow restriction is to reduce blood flow going into the limb, but not completely occlude blood flow.
Jeremy Loenneke
If you want to lift with heavy weights, then just do that. I think the utility of using blood flow restriction is with that you can use lower loads.
Jeremy Loenneke
I think the safety profile overall is comparable to that of high load exercise or traditional exercise.
Jeremy Loenneke
It's about lifting heavy weight is the best way to get better at lifting heavy weight.
Jeremy Loenneke
I am not sure that muscle growth in response to exercise is a mechanism. I've seen no experimental evidence that suggests that that's the case.
Jeremy Loenneke
The morbidity and mortality associated with muscle loss, especially in the elderly, is so significant.
Peter Attia
2 Protocols
General BFR Resistance Training Protocol
Jeremy Loenneke- Apply cuff to the limb and determine the individual's Arterial Occlusion Pressure (AOP) using a Doppler probe.
- Set the cuff pressure to approximately 40% of the measured AOP.
- Select a load that is 20-30% of the individual's one-rep max (1RM).
- Perform 4 sets with the following rep scheme: 30 repetitions for the first set, followed by 15 repetitions for the next three sets.
- Rest for 30 seconds between each set.
- Maintain a controlled pace of approximately one second for the concentric phase and one second for the eccentric phase.
- Limit continuous BFR application to one exercise (approximately 7-10 minutes) when first starting out to gauge tolerance.
Progression of BFR Application in Rehabilitation
Jeremy Loenneke- Phase 1 (Passive Restriction): For individuals unable to exercise (e.g., post-surgery), apply BFR cuffs and inflate/deflate for periods a couple of times a day to slow muscle loss.
- Phase 2 (Low-Intensity Aerobic Exercise): Once able to move, but not lift weights, use BFR during very slow walking or other low-intensity aerobic activities to maintain or slightly increase muscle size and strength.
- Phase 3 (Low-Load Resistance Exercise): When resistance exercise becomes possible, incorporate BFR with light weights (20-30% 1RM) to achieve significant muscle size and strength gains.
- Phase 4 (High-Load Resistance Exercise): If appropriate and desired, transition to traditional high-load resistance exercise, as BFR is not additive to the maximal stimulus of heavy lifting for strength.