My knees went south playing on hard courts. Hard true came late for me. I played both singles and doubles but near the end of tennis days it was only doubles. Won state of Ohio 13 times as a captain of a team. Played 4.0 but as i aged i was plating 3.5 . I am 78 now but told i look 60. Shot my age in golf the other day. When i had first tkr i noticed i lost a lot of speed. I decided on stem cells as my TKR did not go well. Its been 5 years and still have swelling, pain, etc, I love my biking and i do 20 miles each day. Good luck to you.