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How to Restore Volitional Muscle Control

To properly function after an injury or surgery, returning strength back to the involved muscle groups is always essential. In fact, strength is often used as one of our main objective findings we look at when evaluating an injury, or assessing someone’s ability to return to sport.

One thing that any sports physical therapist definitely knows about injuries is that muscle function is almost always inhibited afterward. This is especially true after a surgery.

But why?

Why does quadriceps strength go down after ACL surgery? And why does it often take so long to come back?

I recently got together with my friend Russ Paine from Houston, TX to record a presentation for my Inner Circle on the use of biofeedback in rehabilitation. Russ is one of the best sports physical therapists around and has rehabbed countless NFL, NBA, and MLB stars that you would definitely know. So he has seen a ton of ACLs in high-level athletes in his career.

The loss of strength after an injury was something we talked about, here’s a clip of Russ explaining what happens:

I thought this was really important to understand, and Russ alludes to this at the end. But, when faced with this loss of strength acutely after an injury or surgery, we often perform neuromuscular electrical stimulation to help regain muscle function.

But is there a better way?

Russ and I think so, and often use biofeedback with our athletes. The difference between NMES and biofeedback comes down to volitional control of the muscle.

Russ explains more in this clip from his presentation:

As you can see, biofeedback does a better job at stimulating volitional muscle control. Honestly, this may be the key to early phases of our rehabilitation process.

Rather than using NMES to stimulate the muscle, we can use biofeedback to actively work on improving volitional control.

Get Started with Biofeedback

mTrigger Biofeedback

Until recently, using biofeedback was a little bit harder to do. The devices were old, clunky, and expensive. But Russ and his crew have developed the mTrigger Biofeedback device, which I really think is a game-changer. It’s so easy to use, effective, and affordable. And lucky for you, mTrigger is also giving my readers an additional 10% off:

If you want to keep learning more about biofeedback. Check out Russ’s last article on my site on Why You Should Be Using Biofeedback in Rehabilitation or better yet, watch his full Current Concepts on the Use of Biofeedback in Rehabilitation presentation in my Inner Circle.

Why You Should Be Using Biofeedback in Rehabilitation

This week’s article is an excellent guest post from my friend Russ Paine, PT, discussing why and how we should be using biofeedback in our rehabilitation patients.  Russ and I are both big fans of biofeedback but unfortunately, it’s fallen out of favor because insurance companies don’t reimburse it. But that doesn’t mean it’s not effective.  And now, there’s a new biofeedback device, the mTrigger, that uses an app on your phone that is amazingly easy to use and affordable. I think this is going to be a real game-changer.  And mTrigger was nice enough to offer my readers 10% off if they use coupon code REINOLD! More details below, but check out the article and our video first!


Why You Should Be Using Biofeedback in Rehabilitation

I have been involved in the evaluation and treatment of sports medicine injuries for 33 years.  I have been very fortunate to have a “true” sports medicine practice that predominantly includes professional, college, high school, amateur, and aging athletes.  Having this type of clientele has forced me to explore and pursue restoring full function in the timeliest manner, being very careful to not cause harm using an aggressive approach.  

I believe that one of the secrets to having a successful return to sports with minimal adverse effects is fully restoring muscle function.  

Although many aspects of our field have seen excellent advancements and growth, we continue to combat one of the most difficult challenges following injury and surgery, muscle atrophy, and weakness.  

Restoration of muscle function should not only be measured by muscle force output and scores obtained on functional tests but neurological function. In my practice, establishing normal neurological function following knee surgery is goal number one for our patients’ initial step on the path toward a successful return to function.  

The Use of Biofeedback in Rehabilitation

So how do I do this?  The use of biofeedback is my preferential method of attacking the neurological deficit following surgery or injury.  

New advances in biofeedback devices have recently allowed the ability to provide a general assessment of the patients’ EMG neurological status. The subjects’ ability to fire the inhibited muscle may now be conveniently measured by recording EMG activity of the involved extremity and comparing this to the opposite normally functioning muscle group.

The primary rationale for the use of biofeedback is the belief that the patient should begin to use their own “electrical system” as soon as possible through a volitional contraction. 

The concept known as the order of recruitment lends support to the use of biofeedback to enhance volitional contraction.  This order is based on the size principle. Heinemann’s size principle states that under load, motor units are recruited from smallest to largest. In practice, this means that slow-twitch, low-force, fatigue-resistant muscle fibers are activated before fast-twitch, high-force, less fatigue-resistant muscle fibers.  

When using a biofeedback device, the clinician sets the goal for the inhibited muscle so that a strong voluntary effort is required by the patent for each contraction.  This is visible to the patient and forces a strong contraction to reach the pre-set goal. I believe that voluntary contraction using biofeedback produces the greatest results in restoring muscle function early.

Biofeedback or Neuromuscular Stimulation?

Neuromuscular electrical muscle stimulation (NMES) is often used to stimulate muscle contraction.  There is a vast amount of literature supporting NMES for use during rehabilitation. Until recently, NMES has been a reimbursable modality, thus there was much financial support to research its’ effectiveness.  

Biofeedback has not been reimbursable and that may have had an effect on the comparative lack of literature.  One article from Draper and Ballard supports the use of biofeedback over NMES.  This article compared the two modalities during ACL rehabilitation.  After 6 weeks, the biofeedback group was shown to provide greater quadriceps isometric muscle strength than NMES treated group.

I believe in the use of NMES if a patient is unable to make any voluntary contraction, which sometimes happens following ACL reconstruction surgery.  But, once a patient is able to produce a voluntary contraction, detected by the biofeedback, we immediately switch the patient to biofeedback.

When using NMES, all nerve fibers are stimulated simultaneously.  This, in my opinion, is not as effective as biofeedback because the order of recruitment from small to large diameter nerve fibers is not sequential as is the case with voluntary contraction.  NMES actually recruits the large-diameter nerve fibers first because they are more excitable, as large diameter axons have less resistance to firing. Atrophy of muscles has predominate effects on the slow-twitch smaller diameter Type I  fibers, so recruiting these muscle fibers is critical to reverse the effects of muscle inhibition and atrophy.

How to Use Biofeedback in Rehabilitation

I use biofeedback on virtually every knee patient that has decreased neurological EMG output.  As previously mentioned, we are able to use a new device to provide a side to side assessment of EMG activity.  

This information as also very educational and motivational to the patient as they can see the actual deficit via visual EMG numbers between normal and involved.  

Cycles of 10 seconds on and 10 seconds off are utilized during the 10-minute biofeedback session.  My instructions to the patient for quadriceps re-education are to “tighten your muscle and force your knee straight”.  Progress is continued to be monitored on a weekly basis to measure the change in EMG activity, as shown using the biofeedback application.  

The mTrigger Biofeedback device that we use utilize has an amplifier that sends the measured EMG activity via a Bluetooth signal to an android or IOS device with the appropriately downloaded software application.  

This mTrigger is available for home use as well as clinical use.  Patient reported motivation using this type of biofeedback product is very high as they can actually visualize their intensity of muscle contraction when performing home exercise programs.  There seems to be an interesting psychological connection between the use of one’s personal smartphone or computer pad and their muscle activity.

Lack of extension of the knee has been shown to have an adverse effect on knee function.  Loss of extension alters the gait pattern and can produce abnormal stresses to the patellofemoral joint.  Due to a lack of quadriceps control, many quad inhibited patients will ambulate with a flexed knee gait pattern.  

The use of biofeedback can be used to combat this common malady often associated with post-op care of the knee.  Lacking quad control, patients’ are unable to eccentrically control the knee flexion moment that occurs during single-limb balance.  A quad inhibited patient will assume this flexed knee position because they “know” the position of the knee during single-limb balance.

This sets up the knee for a co-contracted state and presents as muscle splinting until normal muscle tone and function are restored.  This muscle splinting will continue to exacerbate the lack of extension in the knee. Biofeedback can be very effective at addressing this issue.  

With muscle splinting, we want to teach the patient to relax the hamstring muscle during knee extension stretching, thus negating the effect of a contracting hamstring muscle.  The patient is placed in a prone position, with both patella over the edge of the table. Electrodes are placed over the hamstring muscle. Unlike the inhibited quadriceps muscle where we are trying to elicit a more perfect contraction, the biofeedback unit is now used for relaxation purposes.  As the patient uses the relaxation mode of the unit and learns to control the overly active hamstring contraction immediate increase in passive knee extension is observed.

This position is maintained for a 10 minute period.  Once the patient has “learned” to control the hamstring overactivity, a lightweight may be applied for the 10-minute period to produce a low-load long-duration stretch.  Change in knee extension can be measured using heel height difference measurement technique. Dale Daniel described this measurement and showed that 1cm of HHD = 1 degree of flexion contracture.

Note from Mike: That’s a great example of how you would use biofeedback to work reducing muscle activity.  It’s not always used to increase activity. Another way we use it is to use both channels together on 2 different muscle groups.  Imagine doing a bird dog or glute bridge with the pads on the glutes and low back. You would focus on performing the drill with high glute activity and low back activity.  It’s pretty neat.

Return to Play

Return to play is a hot topic in rehab right now.  It’s difficult to determine if the athlete is ready to return to sport.  There are many obstacles when assisting your athlete to the ultimate goal of returning to sport with pre-injury level of performance.  

Too often, a shift is made during the rehabilitation process to more functional activities and reduced emphasis on strengthening.  If your patient continues to possess a decreased EMG signal compared to the normal side, it will be highly unlikely that they will be able to resume the pre-injury level of function.  

With biofeedback, we have a tool that makes certain that we have completed one of the early critical steps in the process of rehabilitation – restoring and measuring the normal neurological function of the inhibited muscle group.  Don’t allow decreased EMG function to be one of the obstacles to continue to linger.

The mTrigger Biofeedback Device

I thought that was a great article from Russ.  Many don’t even realize how impactful biofeedback can be as it has fallen out of favor.  Here’s a great video from Russ and I demonstrating the mTrigger device and talking about how and why we use biofeedback:

As you can see, the new mTrigger device is so simple to use and completely affordable.  That has always been a limitation in biofeedback devices, they were just to clunky and expensive.

mTrigger biofeedback device

If you want to get started using biofeedback, mTrigger was nice enough to offer my readers 10% off their purchase, making this even more affordable.  Click the link below and be sure to use coupon code REINOLD to get your 10% off

About the Author

Russ Paine, PT, is known for his experience in sports medicine with special interests in injuries to the knee and shoulder, as well as golfing injuries and conditioning. His client list includes many professional athletes who have sought his expertise to help them recover to their prior level of function. Russ has a long career in sports medicine, having served as rehabilitation consultant to the Houston Astros, Houston Rockets, and NASA. Currently the Director of Sports Medicine Rehabilitation at UT Physicians in Houston, TX, Russ continues to devote his time to research and education while maintaining a busy sports medicine clinical practice.  Russ was inducted into the Sports Physical Therapy Hall of Fame in 2018. As a well-established author and lecturer on topics related to sports medicine, he has lectured at over 500 meetings in the US and abroad. He has published 25 chapters in textbooks and over thirty research articles in peer review journals.

Is the Intensity of NMES Important for Strength Gains?

Rotator Cuff NMESNeuromuscular electrical stimulation (NMES) is a common modality used in rehabilitation to help restore function and strength of inhibited muscles.  As our professions continue to grow and expand our goal of restoring “function,” many have moved away from modalities like ultrasound and electrical stimulation, and probably for good reason.  However, I still use NMES frequently in my practice to help kick start my strength recovery after injury or surgery.  I like to superimpose NMES on a muscle that is weak or inhibited to help maximize my gains during both simple isotonic exercises and functional movement patterns.

NMES has bee shown in several studies, too many to cite here, to help restore strength faster than exercise alone following surgeries such as ACL reconstruction and total knee replacements.  Furthermore, I have publish and presented on how I use NMES for the rotator cuff after injury and surgery as well.  It appears that patients that have difficulty activating their muscle have difficulty training their muscles at intensities sufficient enough to promote strength gains.

If you want to learn more about how I use NMES for the shoulder, I have a webinar on this topic at RehabWebinars.com.  I definitely recommend you try this as I can honestly say this is something that I do that produces really good results.

A common question regarding NMES involves the intensity of the stimulation.  How strong of a stimulation should we be trying to achieve?

Even a Small Amount of NMES is Effective

In my article in AJSM, we reported that peak force production of external rotation with NMES applied was 22% greater than without NMES.  Furthermore, the increase in peak force production was not significantly different based on the intensity of the stimulation.  Essentially, it didn’t matter how high you turned up the ESTIM, you still saw a nice increase in force production.

Even low thresholds of NMES intensity could result in altered motor unit recruitment and subsequent improvement in muscle function.  This doesn’t mean that a small amount of NMES is best, it just means that if you have a patient that doesn’t tolerate a strong contraction, it is still going to provide some benefit and is worth performing.

The More NMES Intensity the Better

A recent study was published in the journal Physical Therapy looking at the relationship between intensity of quadriceps NMES and strength recovery after total knee replacement.  The authors concluded that there is a relationship between NMES intensity and change in torque and muscle activation.  This is similar to past finds by Lynn Snyder-Mackler and her group that have published extensively on NMES.

While it does appear that “the more, the better” may be true, we should also careful consider the amount of discomfort and, if the patient is postoperative, the tissue healing status.  We certainly don’t want to increase the patient’s pain to a level of perceived threat that may cause a negative effect on recovery.  Because we know that even a small amount of NMES is beneficial, I generally use the patient’s comfort level as my guide.  Patients are often apprehensive when receiving NMES for the first time.  As their tissue heals and they become more comfortable, you will naturally be able to raise the NMES intensity to maximize gains.  My comment is always “the more the better, but I would like it to be comfortable.”

NMES

What has your experience been with NMES?  Are you using NMES more or less in recent years, and why?

To learn more about how I use NMES for the shoulder following injury and surgery, check out my webinar at RehabWebinars.com.

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