Tennis, question about bending your knees?

Question

I know you need to bend your knees to get more power but, during the stroke, do you extend your knees or do they stay bent the whole time?

Answer 1

As you make contact, both rotate your body and extend your knees. This will help you get more power and topspin respectively.

Answer 2

Extend

Answer 3

extend your knees to complete the stroke