WOMAC Physical function assessment

HI

I am getting introduced to the WOMAC score . I think it is simple and good, however I am finding some difficulties determining physical function.
most of the times the patient answers are biased by pain. so What is the best method to ask physical function question
Should I ask the patient to perform the task and i evaluate ? or just ask the patient on their level of difficulty in performing the task?

if his answered on his physical function level was biased by pain should i correct him.

some examples of questions would help.

Thanks