Dog suddenly reluctant to jump

7 year old golden retriever, seemingly out of the blue he’s reluctant to jump in bed, on the couch or in the car. He’s still running around and nothing else seems out of norm, doesn’t seem sensitive to touch anywhere and if he’s bribed say with a tennis ball he will jump on up without a second thought. Not overly concerned since he seems totally fine otherwise, but any thoughts on what might be going on?