Biofeedback is Critical Care for Knee Injury Rehab

By |2021-07-20T10:14:07-04:00January 10th, 2021|Latest Articles|

Knee injuries are some of the most common issues treated in physical therapy. The lower body experiences significant impact and wear and tear during sports, fitness, and everyday life. Such activity can inflict damage as a result of falls, collisions, quick changes in direction, over-use, and more. Knee injuries like patellofemoral syndrome or a torn ACL can be devastating for athletes, resulting in months of physical therapy and lost play. The general public also represents their fair share of knee pathologies, with recent spikes in conditions such as osteoarthritis. Osteoarthritis is caused by wear and tear from aging, overuse, and obesity, and is painful and irreversible, usually resulting in a total knee replacement. Because the functionality of the knee impacts so much of our daily lives – and for some, their livelihood directly – efficacy of treatment following injury and/or surgery is critical. 

When rehabilitating various knee injuries, the main focus is to strengthen and regain range of motion. Overall, various knee injuries have similar treatment plans, with the main difference being changes in pathology from patient to patient. The most important part of the treatment plan is turning the quad back on. The quad experiences the most inhibition from pain and swelling after a knee injury, with its EMG output dropping by up to a whopping 50%! Another primary goal of treatment is to regain extension of the knee, which is achieved via exercises that force the knee to straighten. As the quad becomes re-engaged and range of motion improves, physical therapists can work back up to walking exercises and running. After six months post-op, treatment can re-focus on strength and conditioning in preparation to get back into sport around 8 months. Using biofeedback during this process speeds up recovery time by making the most out of every single muscle contraction. We believe that biofeedback should be in the tool arsenal of every expert looking to provide high quality care that gets results for their knee patients.


Why Biofeedback?

Knee treatment is so fundamental to mTrigger’s development that we were talking about it when we first launched back in 2018! Check out Russ Paine and Mike Reinold discussing the basics of getting set up on the knee here:

The mTrigger®️ Biofeedback System senses the electrical current produced by motor neurons and transmits that data to a visual display for physical therapists and patients to observe. sEMG biofeedback helps patients witness and improve control over subtle changes in muscle activation that occur during therapeutic exercise. 

Such observation allows us to assess somatic awareness and neuromuscular functionality by making the invisible visible. Improving control over voluntary muscle activity – whether relaxing during muscle inhibition or contracting for strengthening exercises – will help your patients reach their goals faster. sEMG biofeedback provides real-time data that ensures patients understand how to perform their exercises effectively; in turn, more accurate reps speed motor learning, strength gains, and recovery. Audiovisual feedback educates patients and informs clinicians so that everyone gets the most value possible from every rep. Additionally, visual stimuli motivates patients, adding a competitive nature to training sessions and building consistent, accurate recruitment patterns with long term impact. Learn more about the mechanisms of muscular recruitment here and read on to dig into the benefits for knee treatment!


Tell Knee About It!

Target muscles for rehabilitation after knee injury or surgery are the quad and hamstring. In general, when rehabbing a knee injury, patients are taught to relax their hamstring and strengthen quad activation.

ACL injuries – usually the result of twisting and pivoting – are the most common knee injury and the most time-consuming to rehabilitate. ACL injury predominantly occurs in people that have lost dynamic control of the knee and don’t have the same fitness level as they once did. Being out of shape makes knee injury much more likely, and women are seven times more likely to injure their ACL! Sports that rely on jumping, such as basketball and volleyball, cause a lot of knee injury, and high-contact football is also an offender. Hot tip: Practice injury prevention by incorporating a jumping program that teaches patients how to land properly and safely

After knee injury, quad “firing” is reduced because swelling and pain in the knee lead to muscle inhibition. This condition has many potential implications, including quad atrophy and weakness, changes in gait pattern, and compensation from other muscles like the hamstring or glute med. Naturally, then, one of the primary goals in physical therapy for knee rehabilitation is to re-engage the quad. By placing electrodes either to target the whole muscle group, or to isolate a single muscle such as the VMO (more on electrodes here), you can show your patient the strength of their muscle contraction on the mTrigger app. The main training display consists of a red-to-green activation scale, whose max contraction goal can be adjusted to reflect the neuromuscular output of each individual patient. Hitting the green zone of the scale indicates the patient is reaching their maximum activation potential for that exercise, and our rep counter encourages them to hit that goal on every rep. There is no faking it with mTrigger, and your patients will certainly feel their quad contracting! 

Inhibition training can also be critical to patient success and return to function following knee injury. One particular area of note is in hamstring tonicity and guarding: achieving restoration of gait requires full knee extension; but after trauma, it is common to see hypertonicity in the hamstring that prevents full extension. The hamstring has a pivotal role in protecting the knee, and often recovers much more quickly than the quad – so it’s critical to start this training early. See a demonstration here of the use of biofeedback to reduce heel height difference via relaxation training.

Quad exercises are also a fantastic way to utilize mTrigger’s dual channel setting once some of that early inhibition is overcome with isometrics and quad sets. One setup option is bilateral comparison, which involves placing electrodes on the injured (channel 1) and uninjured side (channel 2) to compare muscle activation in real time. Another potential setup monitors compensation: place electrodes on the quad (channel 1) AND hamstring (channel 2), both on the injured side, if your patient is experiencing difficulty with compensation; this will help them identify and reinforce the proper recruitment patterns during knee extension.

Take it from Russ Paine:

“Don’t stop using the mTrigger too early! You should start your sessions with the mTrigger to identify the initial EMG deficit, but it is highly important to keep using the mTrigger in every single session. You have to keep teaching your patients to tone and recruit slow twitch muscle fibers since they are the most affected by the atrophy.”

Biofeedback can be used to strengthen, isolate, improve fine motor control, or actively inhibit specific muscles during exercise. This versatility allows you to target a plethora of issues that can accompany knee rehab. Customize electrode placement, resistance, and goal and time settings to fit your existing programs, or get creative – biofeedback is all about increasing awareness and control over the body to get outcomes!


mTrigger Set-up

To connect the mTrigger to a phone or tablet, simply power on, head to the mTrigger App and hit “Connect” in the top right corner.

Start your MVC (maximum voluntary contraction) goal around 1000 microvolts and have your patient perform a contraction. If the feedback meter hits the green zone easily, increase the MVC goal. If the patient contracted as hard as possible and was not able to get out of the red or orange zone, decrease the MVC goal to make it slightly easier to get in the green zone. We want to hit the sweet spot of getting that goal at the level of maximum contraction to achieve visual feedback that’s both motivating and challenging!


How mTrigger’s Games Improve Performance

Using the mTrigger during therapy sessions is so beneficial because you can see the level of intensity of each muscle contraction. mTrigger is also helpful in identifying the initial level of EMG deficit at hand. One of the most effective ways to use mTrigger for knee injury rehabilitation, though, is the Play module: mTrigger games vastly increase muscle activation by forcing patients to work harder. The games are fun and engaging, thereby ensuring patients are entertained enough to stay focused.

MuscleBall is excellent for quad activation, and FlexSledding is very effective for straight leg raises. Using the Train feature is very useful for visual feedback, but don’t sleep on the games, where you’ll see loads of engagement and activation!


To Wrap Up

Knee injury is extremely common in physical therapy clinics due to high loading in multiple directions during sports and everyday life. To achieve and maintain healthy activation patterns, it is extremely important for people to have control of their bodies in and out of therapy. Invest in an mTrigger to improve patient awareness and mastery of volitional muscle activation. We guarantee you’ll see results that improve both speed and longevity of return to function. 



“We feel as though our patients/athletes primarily benefit from implementation of the mTrigger post surgically in order to enhance quad tone as well as strength and speed of contraction following inhibition caused by surgery. Patients also benefit from the feedback when performing exercises that require terminal knee extension.” – Sean, PT | ID


“This is the first time that I’ve really felt my quads working during this exercise and the first time I’ve been aware of how to fire them.”     -Ray, mTrigger Patient | NY


“The mTrigger gives you more of a workout [than just electrical stimulation]. It actually shows you how you’re doing and lets you know if you are doing it right, whereas the e-stim just does it for you. I felt it was more beneficial for me to use the mTrigger since it was letting me know if my quad was actually firing or not. It was easier for me to have a visual cue than just believing that I was contracting my quad.”     – Kyle, mTrigger Patient | NE


“The mTrigger device is the best clinical tool to come along in 10 years. It is a must for all clinicians treating Orthopedic case loads. It fills in a gap in our treatment programs when patients – due to trauma or pain – simply cannot turn back on these muscles due to neurological inhibition. I have had tremendous success with the most difficult patients helping to restart their Quads, Rotator Cuff, or peroneals etc. Again, a must technique to add to your clinical tool box.”     – Mike, PT | MI


Other articles of interest:

Case Study: Reflection on “Actively” Rehabbing after Medial Meniscectomy

Top Clinical Applications for the mTrigger Biofeedback System

Addressing Muscle Atrophy in Post-op Knee Patients

Quad strength + return to function

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