What is arthrogenic muscle inhibition (AMI)?

• A. Inability to fully activate a muscle (prevents CNS from fully activating)
• B. Enhanced muscle activation
• C. Improved motor unit recruitment
• D. Increased endurance of affected muscles

Answer: (A)

Arthrogenic muscle inhibition is a neural response after joint injury that reduces activation of the surrounding muscle. Damaged or inflamed joints send abnormal signals to the nervous system, which protective reflexively dampens the alpha motor neurons feeding the agonist muscle. The result is an inability to fully recruit motor units during voluntary contraction, so strength looks diminished even though the muscle tissue itself could be fine. This inhibition is a protective mechanism to limit further joint stress, but it can persist and impair function.

In NMES context, this explains why a patient may not achieve full activation with voluntary effort alone—the neural drive is compromised. Electrically stimulating the muscle can help recruit fibers directly and support rehab, even if the person can’t fully activate the muscle on their own. The other options describe enhanced activation, better motor unit recruitment, or increased endurance, which do not reflect what AMI entails.