Helping Patients With Knee OA Find—and Use—Their Quadriceps

Knee osteoarthritis (OA) is often discussed in terms of cartilage loss and joint degeneration, but the functional picture is broader. Pain, stiffness, swelling, reduced activity, and impaired quadriceps activation can reinforce one another. When the quadriceps become difficult to recruit, patients may avoid loading the involved leg, lose strength, and find everyday activities such as rising from a chair, climbing stairs, or walking increasingly challenging.

Exercise remains a cornerstone of conservative knee OA management. The clinical challenge is that prescribing an exercise does not guarantee that the intended muscle is working effectively. For patients who have difficulty finding or sustaining a quadriceps contraction, surface EMG biofeedback can make that otherwise invisible effort easier to understand and repeat. mTrigger uses surface electromyography (sEMG) to translate voluntary muscle activity into real-time visual and auditory feedback. Instead of relying only on cues such as “tighten your thigh,” the clinician can give the patient an objective target and immediate visual information about each attempt.

What the Research Supports

Research examining EMG biofeedback during quadriceps exercise in knee OA supports several practical concepts:

• Biofeedback can help patients recognize and sustain a voluntary quadriceps contraction
• A visible or audible target can encourage active participation during repetitive exercise
• Repeated isometric exercise with EMG biofeedback has been associated with improved quadriceps strength and reduced pain
  

These findings suggest that biofeedback can complement progressive strengthening by helping patients achieve more effective and consistent quadriceps contractions, particularly when impaired activation limits exercise performance.

Applying the Evidence with mTrigger 

Given these findings, mTrigger may be particularly useful for a patient who:

• Has difficulty initiating or sustaining a quadriceps set
• Demonstrates quadriceps inhibition or side-to-side asymmetry
• Shifts away from the involved leg or compensates with other muscles
  
• Has difficulty understanding verbal or tactile activation cues
• Is hesitant to load the quadriceps because of pain or low confidence
  

Getting Started

After cleaning the skin, place the electrodes over the selected superficial quadriceps region, following the muscle fibers and the mTrigger placement guide. Research protocols have commonly monitored the VMO and rectus femoris, but the clinical goal should be broader than isolating one part of the quadriceps. Select the placement that reflects the patient’s activation deficit and the exercise being trained.

Watch several practice contractions. Confirm that the signal rises with the intended quadriceps contraction and returns toward baseline during relaxation. Watch for substitutions such as lifting the hip, holding the breath, or pressing excessively through the opposite leg.

Choose an Achievable MVC Goal

Use the patient’s initial contractions to establish a target that is challenging but repeatable. A painful or highly inhibited patient may require a lower starting threshold. The goal is not the highest possible number; it is a deliberate contraction with good technique and an acceptable symptom response.

Begin with a simple contract and relaxation exercise such as a quad set. Ask the patient to raise the activation meter above the target, sustain it without compensating, and then return toward baseline (relax). Increase the target as performance improves, considering contraction quality, pain, fatigue, and consistency across the set.

Progress From Activation to Function

Once the patient can sustain a consistent signal, progress to exercises that require quadriceps activation during movement:

• Seated terminal knee extension
• Straight-leg raise initiated with a quadriceps set

• Supported sit-to-stand
• Mini-squat or wall-supported squat

• Step-up and controlled step-down

During a straight-leg raise, establish the quadriceps contraction before lifting and maintain it without an extension lag.

During sit-to-stand or a step-up, use feedback to reduce unloading of the involved leg and reinforce quadriceps contribution throughout the task.

By helping a patient first recognize and reproduce an effective quadriceps contraction, then reinforce that activation during increasingly challenging movements, and ultimately help transfer improved muscle control into loaded, functional tasks. In this way, mTrigger evolves with the exercise program rather than serving as a tool for only one stage of treatment.

Gradually Remove Feedback

The goal is independent quadriceps control, not permanent reliance on the device. Once the patient is consistent, intermittently remove visual or auditory feedback and ask them to predict contraction quality. Briefly restore the feedback to check accuracy and strengthen the connection between the external signal and the patient’s internal sense of activation.

Keep the Signal in Context

sEMG amplitude is not a direct measurement of muscle force. Electrode placement, skin preparation, subcutaneous tissue, fatigue, movement artifact, and device settings influence the signal. Keep conditions consistent when comparing performance across sessions.

Monitor progress beyond the mTrigger display, including pain response, quadriceps strength, chair-rise performance, walking tolerance, stair function, and patient-reported outcomes. A higher signal matters when it accompanies better movement, increased loading tolerance, and improved function.

mTrigger is one component of a comprehensive successful knee OA program that includes progressive strengthening, aerobic activity, education, self-management, and neuromuscular training as appropriate.

Summary

Research supports EMG biofeedback as a practical way to reinforce quadriceps activation during exercise for knee OA. mTrigger turns muscle activity into immediate, understandable feedback that can improve awareness, participation, and consistency. Begin with an achievable contraction, progress into loaded and functional tasks, and gradually reduce feedback as the patient develops independent control.

More on mTrigger for Knee OA

Using mTrigger with Older Adults 

References

1. Anwer S, Equebal A, Nezamuddin M, Kumar R, Lenka PK. Effect of gender on strength gains after isometric exercise coupled with electromyographic biofeedback in knee osteoarthritis: A preliminary study. Ann Phys Rehabil Med. 2013;56(6):434-442. doi:10.1016/j.rehab.2013.06.001
2. Choi YL, Kim BK, Hwang YP, Moon OK, Choi WS. Effects of isometric exercise using biofeedback on maximum voluntary isometric contraction, pain, and muscle thickness in patients with knee osteoarthritis. J Phys Ther Sci. 2015;27(1):149-153. doi:10.1589/JPTS.27.149