Blood Flow Restriction Training and sEMG Biofeedback

History

Bloodflow restriction training, or BFR, is far from a new discovery. However, its use in rehabilitation over the last decade has greatly increased in popularity. The concept of blood flow restriction was initially discovered in 1966 by Yoshiaki Sato in Japan after he injured his lower leg and was placed in a cast for 6 weeks. He spent that time sitting cross-legged, as is common in Japanese culture, and essentially restricted blood flow to his lower leg. When the cast was removed 6 weeks later, he surprisingly had no atrophy. Fast forward to the early 90’s, and clinical units for blood flow restriction training started to enter the market; but it wasn’t until around 2012 that this intervention really took off.

How it Works 

Blood flow restriction training creates a hypoxic environment in the muscle, meaning an environment that lacks oxygen. This causes cellular swelling, activates protein synthesis, causes intramuscular anabolic signaling, increases growth hormone, and increases muscle fiber recruitment.^1,2 Through these mechanisms, blood flow restriction training can elicit muscular hypertrophy and strength adaptions in a tissue that may be load compromised. The addition of light external loads – 20-30% of one repetition maximum (1 RM) to BFR – is necessary to optimize these cellular effects.³ BFR is popular in rehabilitation settings where the goal is to improve overall muscle hypertrophy and strength, but you are still dealing with healing soft tissues and joint complexes.³ Furthermore, the addition of BFR has been shown to increase the neuromuscular activation and MVC (maximum voluntary contraction) of targeted muscles 15 minutes after BFR was applied.^4,5

The ability of a muscle to generate force depends on the balance between motor unit recruitment and development of muscular fatigue, which occurs due to a lack of oxygen delivery to the muscles.⁶ When lacking oxygen and under fatigue, the force producing capacity of exercising skeletal muscles are slightly altered.⁶ When exercising with BFR, there is a greater decline in the maximal voluntary isometric muscle contraction (seen as a decrease in force production) compared to lower pressures or no BFR intervention at all.⁷ Especially under isometric conditions, the maximum voluntary contraction EMG amplitude is greatly reduced: 72.5% at low pressure vs. 46.3% of maximum EMG activity at higher pressures.⁴ However, in order to maintain force output levels during BFR when under accelerated fatigue, motor units of high threshold excitability are recruited. Therefore, a hypertrophic stimulus would be provided to a greater proposition of the muscle fibers, creating an increased level of myoelectric activity in resistant exercise with BFR.⁸ The use of BFR targets the recruitment of Type II fast twitch muscle fibers⁴, the same type of muscle fiber that is first to atrophy.

Layering BFR with Other Modalities

Similarly to BFR, visual biofeedback as an adjunct intervention for physical therapy has been transformed and modernized over the last several years as well. The use of visual biofeedback has demonstrated greater increases in muscle activation and greater improvements in exercise form compared to verbal and audio feedback.⁹ When muscle activation is minimal, simply being able to see changes in muscle activation levels is a huge motivating factor for patients. Furthermore, it gives them a goal, purpose, and intention to their training that they are often missing.  For one study, real time visual biofeedback on quad muscle activation was provided to assist participants in maintaining a sustained quadriceps contraction.¹⁰

Previous research has shown an additive effect when BFR is paired with electrical stimulation.^3,11,12 In fact, the two together demonstrated a greater increase in strength compared to either intervention alone.¹³ Unfortunately, NMES is not always readily available, and some patients do not tolerate the uncomfortable sensation of electrical stimulation very well.

Surface EMG has been shown to be effective at picking up differences in muscular activation and fatigue during both BFR training and non-BFR conditions.¹⁴ Visual biofeedback using mTrigger is an excellent supplement to BFR training. This addition of visual biofeedback provides a critical element of insight and motivation to the patient rehabbing. As Johnny Owens, founder of Owens Recovery Science BFR System puts it, “mTrigger forces patients to keep recruiting, even when BFR is really, really hard; that way, the patient can have buy in.”

Clinical Applications

Here are a few exercises commonly used with BFR, with the addition of mTrigger visual biofeedback. Notice how sEMG activation levels change with the addition of BFR!

1. Quad Set

1. Using single or dual channel, place the electrodes on the quadricep muscle (VMO and rectus femoris, or two on the VMO) of the involved side (and healthy side if working on bilateral activation). If using dual channel, make sure you are also using BFR on both sides.
   
2. Set up time parameters to 5 sec contraction and 5 sec relax for 60-90 sec total.
   * We recommend starting with a 5-10s isometric contraction at the top of the exercise and progressing from there as strength and stamina improve.
3. Instruct patient to activate their quadricep muscle while performing a long arc quad, trying to get their leg all the way straight.
4. As the patient performs the exercise, they are instructed to increase the muscle activation meter and to maintain that high level of isometric contraction before resting.
5. SAVE the session.
6. Go into “Track” and view the average MVC and chart; how does fatigue affect each rep?

Use the same set up but with the addition of BFR: At the end of your session be sure to save the session and reference the data!

2. Straight Leg Raise

1. In single channel mode, place the electrodes on the quadricep muscle (VMO and rectus femoris or two on the VMO) of the involved side. See photo above.
2. Set 5 sec on and 5 sec off for 60-90 sec.
3. Instruct the patient to activate their quad muscle and perform a straight leg raise. As the patient performs the exercise, they are instructed to increase the muscle activation meter and maintain that high level of isometric contraction at the top of the exercise before lowering down and resting.
4. SAVE the session.
5. Go into “Track” and view the average MVC to see how fatigue affects each rep.

Use the same set up but with the addition of BFR: At the end of your session be sure to save the session and reference the data!

3. Squat

1. Using dual channel, place one set of electrodes on the right quadricep (VMO and rectus) and one set on left quadricep.
2. Set 5 sec on and 5 sec off for 60-90 sec.
3. Instruct patient to perform a squat (back squat, kettlebell squat, body weight squat) slowly and smoothly.
4. As the patient performs the exercise, they are instructed to increase the muscle activation of their quadricep muscle then sustain that increased level of activation throughout the exertion of the exercise. Both meters should increase together to indicate equal weight and activation.
5. SAVE the session.
6. Go into “Track” and view average MVC and see how fatigue affects each rep.

Use the same set up but with the addition of BFR: At the end of your session be sure to save the session and reference the data!

Summary:

BFR creates a hypoxic environment within an exercising muscle that promotes protein synthesis and increased muscular activation. The use of BFR in addition to low loads (20-30% 1RM) can be highly beneficial for improving strength of healing tissues. The layering of sEMG visual biofeedback to the application of BFR can enhance the effects when used together. By providing motivation, increasing hypertrophic stimulus to a greater proposition of the muscle fibers, and improving activation on every rep, BFR and mTrigger visual biofeedback are more effective when used together.  

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References:

1. Scott BR, Slattery KM, Sculley D V., Dascombe BJ. Hypoxia and resistance exercise: a comparison of localized and systemic methods. Sports Med. 2014;44(8):1037-1054. doi:10.1007/S40279-014-0177-7
2. Yasuda T, Loenneke JP, Thiebaud RS, Abe T. Effects of blood flow restricted low-intensity concentric or eccentric training on muscle size and strength. PLoS One. 2012;7(12). doi:10.1371/JOURNAL.PONE.0052843
3. Patel S, Amirhekmat A, Le R, Williams III RJ, Wang D. Osteochondral Allograft Transplantation in Professional Athletes: Rehabilitation and Return to Play. Int J Sports Phys Ther. 16:2021. doi:10.26603/001c.22085
4. Lauber B, König D, Gollhofer A, Centner C. Isometric blood flow restriction exercise: acute physiological and neuromuscular responses. doi:10.1186/s13102-021-00239-7
5. Nie J, Dankel SJ, Laurentino GC, et al. Blood Flow Restriction During Futsal Training Increases Muscle Activation and Strength. 2019. doi:10.3389/fphys.2019.00614
6. Hammer SM, Alexander AM, Didier KD, Barstow TJ. The Journal of Physiology C 2020 The Authors. The Journal of Physiology C 2020 The Physiological Society. J Physiol. 2020;598:4293-4306. doi:10.1113/JP279925
7. Head P, Waldron M, Theis N, David Patterson S. Acute Neuromuscular Electrical Stimulation (NMES) With Blood Flow Restriction: The Effect of Restriction Pressures. J Sport Rehabil. 2020;30(3):375-383. doi:10.1123/JSR.2019-0505
8. de Queiros VS, de França IM, Trybulski R, et al. Myoelectric Activity and Fatigue in Low-Load Resistance Exercise With Different Pressure of Blood Flow Restriction: A Systematic Review and Meta-Analysis. Front Physiol. 2021;12:786752. doi:10.3389/FPHYS.2021.786752/FULL
9. Riek LM, Pfohl K, Zajac J. Using biofeedback to optimize scapular muscle activation ratios during a seated resisted scaption exercise. J Electromyogr Kinesiol. 2022;63:102647. doi:10.1016/J.JELEKIN.2022.102647
10. Arkov V V, Abramova TF, Nikitina TM, et al. Cross Effect of Electrostimulation of Quadriceps Femoris Muscle during Maximum Voluntary Contraction under Conditions of Biofeedback. Vol 149.; 2010.
11. Lorenz D. Clinical Viewpoint Blood Flow Restriction: Cause for Optimism, But Let’s Not Abandon The Fundamentals. Int J Sports Phys Ther. 16:2021. doi:10.26603/001c.23725
12. Natsume T, Ozaki H, Saito AI, Abe T, Naito H. Effects of Electrostimulation with Blood Flow Restriction on Muscle Size and Strength. Med Sci Sports Exerc. 2015;47(12):2621-2627. doi:10.1249/MSS.0000000000000722
13. Slysz JT, Burr JF. The Effects of Blood Flow Restricted Electrostimulation on Strength and Hypertrophy. J Sport Rehabil. 2018;27(3):257-262. doi:10.1123/JSR.2017-0002
14. Hotta GH, Queiroz POP, de Lemos TW, Rossi DM, Scatolin R de O, de Oliveira AS. Immediate effect of scapula-focused exercises performed with kinematic biofeedback on scapular kinematics in individuals with subacromial pain syndrome. Clin Biomech. 2018;58:7-13. doi:10.1016/J.CLINBIOMECH.2018.07.004