hi,
I think you decide to check teh muscle strength depending upon the voluntary control that the patient has on the affected limb!! for easy reference,
assess the spasticity of the limb if it is more that 2 mas then you know that the patient may (if he has some voluntary control) use spasticity to move!! If the spasticity is less that 2 mas, the assess his voluntary control and if it ins more than grade four in the brunstroms scale then you can assess the muscle strength!!