My right knee is sore and strengless sometimes, especially stepping downstairs after getting up in the morning and long-time sitting.
When I jump, I can feel the right knee is not strong enough.
What is wrong with it?
Thanks for any concern.

How old are you?

41 years old.

You would most likely need to see an orthopedic doctor about this. There is no way we can diagnose what is wrong with you over the internet.

There is too much about your lifestyle now and when you were younger, among MANY other factors that we do not have access to.

z, At your age, it is likely that any number of things could be giving you problems with you knee. Could be stretched ligaments, arthritis, bone rubbing on kneecap, soft tissue(muscle)irritation due to disease or injury of some sort.

YOu really need a professional, a physician, to manipulate and examine your knee to help you get answers. :)

Best wishes,