After surgery, many people experience difficulty activating their muscles the way they used to. This phenomenon, known as arthrogenic muscle inhibition (AMI), is particularly common after knee surgeries, where it significantly impacts the quadriceps muscles (front of the thigh). If left untreated, AMI can slow recovery, delay strength gains, and lead to long-term complications.
Arthrogenic muscle inhibition occurs due to a combination of factors that reduce muscle activation after surgery.
The central nervous system (CNS)—which includes the brain and spinal cord—sends signals to muscles, telling them to contract. However, after surgery, this communication becomes impaired. Research shows that patients recovering from knee surgery, such as ACL reconstruction, struggle with voluntary quadriceps activation1. Interestingly, when electrical stimulation is used to bypass the CNS, muscle contraction strength increases, highlighting the nervous system’s role in AMI.
ACL injuries further complicate this issue, as the torn ligament causes a loss of sensory input from specialized nerve receptors, disrupting normal muscle function2.
Swelling is another key factor in AMI. Post-surgical swelling has been repeatedly shown to decrease muscle activation, though this effect lessens over time with proper management3. This is why ice, elevation, and compression are crucial early in the recovery process. As you get further away from surgey, this becomes less important as swelling decreases with treatment.
If AMI isn’t resolved, it can alter movement patterns and increase the risk of long-term joint issues.
Research shows that patients recovering from ACL surgery with prolonged quadriceps weakness land harder on their operated leg while walking, increasing force through the knee joint instead of absorbing impact through the muscles4. Over time, this altered gait pattern can lead to pain and further compensations affecting other parts of the legs and back. After surgeries like knee replacements managing AMI can also help to reduce post-surgical pain by decreasing the force through the new joint and putting more of it into the quadriceps.
Limited quadriceps strength after ACL repair may be associated with a higher likelihood of developing osteoarthritis, likely due to increased joint stress5. Since AMI contributes to persistent muscle weakness, addressing it early can reduce the risk of arthritis.
A combination of treatment strategies is often the most effective way to improve muscle activation after surgery.
NMES is one of the most common tools for combating AMI. This technique involves placing electrodes over the affected muscle and using electrical impulses to force the muscle to contract. Since this bypasses the nervous system, it helps improve voluntary muscle contraction later on. NMES is frequently used early in the recovery after ACL surgery or knee replacement but some protocols have found a benefit using it for up to 3 months post operatively to help strength come back more fully6. Combining NMES with traditional exercises like quadriceps squeezes or leg extensions has also been shown to improve strength gains more than exercise alone7.
Some studies suggest that icing the knee can improve quadriceps activation by increasing activation of certain neurons which in terms helps to overcome the inhibition from AMI8. While more research is needed, icing can also be combined with TENS, a type of electrical stimulation that helps manage pain.
While BFR training does not directly improve AMI, it can help limit muscle atrophy during the early stages of recovery. Since AMI makes it harder to fully activate muscles, BFR training allows for muscle maintenance with lower-intensity exercise, reducing strength loss. (For more details on BFR training, check out our previous blog post here.)
Arthrogenic muscle inhibition is a common and often overlooked challenge after surgery, particularly for knee surgeries like ACL repair and knee replacement. Since AMI can contribute to joint stress, muscle loss, and an increased risk of osteoarthritis, addressing it early is crucial for long-term recovery.
If you’re preparing for, or recovering from knee surgery, our team at Maven can help you regain strength and function faster. Contact us today to start your personalized rehabilitation plan!
1. Hopkins, J. Ty, and Christopher D. Ingersoll. “Arthrogenic Muscle Inhibition: A Limiting Factor in Joint Rehabilitation.” Journal of Sport Rehabilitation, vol. 9, no. 2, May 2000, pp. 135–159, https://doi.org/10.1123/jsr.9.2.135.
2. Needle, Alan R et al. “Central Nervous System Adaptation After Ligamentous Injury: a Summary of Theories, Evidence, and Clinical Interpretation.” Sports medicine (Auckland, N.Z.) vol. 47,7 (2017): 1271-1288. doi:10.1007/s40279-016-0666-y
3. Palmieri-Smith, Riann M et al. “Pain and effusion and quadriceps activation and strength.” Journal of athletic training vol. 48,2 (2013): 186-91. doi:10.4085/1062-6050-48.2.10
4. Shi, Huijuan et al. “The relationship between quadriceps strength asymmetry and knee biomechanics asymmetry during walking in individuals with anterior cruciate ligament reconstruction.” Gait & posture vol. 73 (2019): 74-79. doi:10.1016/j.gaitpost.2019.07.151
5. Palmieri-Smith, Riann M, and Abbey C Thomas. “A neuromuscular mechanism of posttraumatic osteoarthritis associated with ACL injury.” Exercise and sport sciences reviews vol. 37,3 (2009): 147-53. doi:10.1097/JES.0b013e3181aa6669
6. Fitzgerald, G Kelley et al. “A modified neuromuscular electrical stimulation protocol for quadriceps strength training following anterior cruciate ligament reconstruction.” The Journal of orthopaedic and sports physical therapy vol. 33,9 (2003): 492-501. doi:10.2519/jospt.2003.33.9.492
7. Snyder-Mackler, L et al. “Strength of the quadriceps femoris muscle and functional recovery after reconstruction of the anterior cruciate ligament. A prospective, randomized clinical trial of electrical stimulation.” The Journal of bone and joint surgery. American volume vol. 77,8 (1995): 1166-73. doi:10.2106/00004623-199508000-00004
8. Loro, William A et al. “The effects of cryotherapy on quadriceps electromyographic activity and isometric strength in patient in the early phases following knee surgery.” Journal of orthopaedic surgery (Hong Kong) vol. 27,1 (2019): 2309499019831454. doi:10.1177/2309499019831454
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