Biofeedback is Critical Care for Knee Injury Rehab

By |2022-01-14T16:03:52-05:00January 10th, 2021|Latest Articles|

Knee injuries are one of the most common issues treated in physical therapy, with their cause being multifactorial. The lower body experiences significant impact forces during sporting activities and everyday life. With joint forces reaching 2-3x body weight during running and even higher for landing or jumping maneuvers, the wear and tear on the knees during such activity adds up. Knee injuries as a result of falls, collisions, quick changes in direction, or over-use can be devastating for athletes, resulting in months of physical therapy and lost play. 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 population also represents a significant portion of knee pathologies, with recent spikes in conditions such as osteoarthritis. Osteoarthritis is caused by a progressive loss of the cartilage surface that protects the knee joint. Over time the issue can become more pronounced, leading to pain, loss of function, and ultimately a total knee replacement. The functionality of the knee impacts so much of our daily lives – and for some athletes, it effects their livelihood directly. Therefore, proven and effective treatment following a knee injury and/or surgery is critical. 

When rehabilitating various knee injuries, the overall goal is to regain range of motion, increase strength, and improve movement patterns. Although knee injuries vary by patient and pathology, the foundations of treatment are generally the same. For any knee injury a significant portion of the early treatment plan focuses on learning to turn the quad back on. The quadriceps muscle is meant to support and protect the knee. After an injury, quadriceps inhibition occurs asa result of pain and swelling in the knee. Quad function can drop by up to 50% as measured with EMG output; this is a significant deficit to overcome if not addressed urgently and appropriately.

Another primary goal of treatment is to regain knee extension range of motion, which is achieved via exercises and drills that encourage the knee to straighten. As the quad becomes more efficient and range of motion improves, physical therapists can begin working back to walking and functional activities. Eventually, when appropriate, running, cutting, and jumping should be incorporated. After six months post-op for major knee surgeries, treatment can re-focus on heavy, more intense strength and conditioning in preparation to get back into sport around 9-12 months. Using biofeedback during this process speeds up recovery time by emphasizing the importance of every muscle contraction. By receiving visual biofeedback, each rep is maximized and optimized, teach strong, accurate movement early on. Biofeedback should be in the arsenal of every expert looking to provide high quality care that gets results for their knee patients.


Why Biofeedback?

Optimizing knee treatment has been fundamental to mTrigger’s development we first launched back in 2018! Check out Russ Paine and Mike Reinold discussing the basics of mTrigger for the knee here:

The mTrigger®️ Biofeedback System picks up the electrical current produced by motor neurons within the muscle 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, patterns, or compensations 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 by relaxing a muscle during inhibition or contracting it for strengthening exercises – visual biofeedback will help your patients reach their goals faster. sEMG biofeedback provides real-time data to ensures patients understand how to perform their exercises correctly and effectively. In turn, we see more accurate reps, increased speed of motor learning, strength gains, and improved recovery. Visual feedback helps to educate patients and inform clinicians so that everyone gets the most value out of every rep, exercise, and movement. Additionally, visual stimuli provides motivation for patients, adds a competitive element to training sessions, and builds 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!

The target muscles for rehabilitation after knee injury or surgery include the quad and hamstring. When rehabbing a knee injury, patients are taught activate their quad muscle to protect the knee. Occasionally, working on hamstring relaxation is useful when trying to regain full knee extension motion. Further down the road, hamstring strength becomes a focus to help further protect against knee injuries, especially anterior cruciate injuries (ACL). 

ACL injuries – usually the result of improper twisting and pivoting motions – are the most common knee injury and the most time-consuming to rehabilitate. ACL injury predominantly occurs in athletes and those with neuromuscular movement deficits. Females are seven times more likely to injure their ACL, and the risk of re-tear is significant if not rehabbed correctly. Sports that rely on running, jumping, and cutting – such as basketball, soccer, lacrosse, and volleyball – raise concern for knee injury. Contact sports, such as football and rugby, also present high risk. Hot tip: Practice injury prevention techniques in the pre-season 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 has many potential implications, including quad atrophy, weakness, changes in gait, and compensation from other muscles. Naturally, then, one of the primary goals in physical therapy for knee rehabilitation is to re-engage the quadricep muscle.

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 (increased tone) in the hamstring that prevents full knee 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 a bilateral quad muscle comparison, which involves placing electrodes on the injured side quad (channel 1) and uninjured side quad (channel 2) to compare muscle activation deficits in real time. Another potential setup monitors compensation patterns: place electrodes on the quad (channel 1) AND hamstring (channel 2), both on the injured side, if your patient is experiencing difficulty with hamstring  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 are extremely common in physical therapy clinics due to the high loading and frequent changes in direction that occur during sports and everyday life. To achieve and maintain healthy activation and movement patterns, it is extremely important for patients to have accurate 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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