Originally Posted by NLBwell
Getting off the ground on groundstrokes is not something you do intentionally. It does happen in the right circumstances depending upon your court movement at the time. Of course it is caused by the legs, but it is not an intentional jump (unless you are trying to hit a groundstroke off a really high ball over your head for some reason).
When you try to analyze what is "intentional" or not "intentional, you are entering a very tricky area. I normally hop on every real serve. Is it intentional? I would say at the moment, I am thinking about where I want to hit the ball and what spin I want to put on it and not the hop at all. But at one time the hop was definitely intentional as I was learning. I was also a long jumper in college. I can tell you that once you reach a high level, most of what you are doing is just running on auto-pilot, but it doesn't mean I wasn't still sprinting as fast as I could and jumping.
As corners mentions, David Bailey is explicitly teaching jumping moves to young players. Once the neural pathways are made, most of this stuff will seem subconscious or non-intentional, but it still is jumping or hopping.