"So when you tap into the Speed Force, you have to make sure that you're not pulling out a whole lot more than you need. That's kind of the trick. So it's like... make them move fast, but not too fast. You get the hang of it with practice but you know, during practice..." Bart made the same hand gesture, "Boom. Like a lot."
Surely Tommy already knew about the Speed Force. Bart couldn't imagine a speedster getting to Tommy's skill level with out it (Jay Garrick being the exception because he was old as dirt).