Mixed

Early quadriceps strength loss after total knee arthroplasty is predominantly caused by failure of voluntary muscle activation (neural inhibition) rather than muscle atrophy.

After knee replacement, your leg is weak not just because the muscle shrank, but because your brain is failing to fully recruit it. Since pain isn't the main reason for this 'shutdown,' simply waiting for pain to disappear won't fix your strength. You need active rehabilitation that specifically targets retraining your nervous system to fire the muscle fully, such as high-intensity contractions or neuromuscular electrical stimulation.