Muscle Weakness

paresis - moderate weakness

plegia - severe weakness

It can be difficult to determine UMN vs LMN in situations of acute weakness, as it can take time for signs to evolve

in the arm, extensors are the weakest:
- deltoid, triceps, wrist and finger extensors, finger abductors
in the leg, flexors are weakest:
- psoas, hamstrings, ankle dorsiflexors
spacticity follows the opposite pattern, with antigravity extensors kicking in

Peripheral neuropathy or motor neuron disease

Muscle/NMJ disease