Why does muscle weakness occur after joint injury?

Sure, the muscle crosses the joint - but it isn't damaged. What does the quadriceps have to do with the ACL? Why the profound weakness?

This phenomonen is called arthrogenic muscle inhibition (AMI). It is a protective mechanism to avoid use of the injured joint.

Essentially, damage to ligamentous, boney, and mensical structures combine with swelling and pain to disrupt sensory input. The motor side of the system is ultimately shut-off to protect the joint.

Patients are unable to fully contract (e.g., neurologically engage) their muscle during exercise due to inhibitory signals flooding the spinal cord.

Unfortunately, this inability to fully contract the muscle limits our progress in rehabilitation. Further, our ineffective muscle-centric approaches (e.g., quadriceps strengthening programming) treat the symptom of muscle weakness, and not the neural source of the impairment.

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