I’ve heard lots of explanations about getting power into your serve. This is the best I’ve ever found. The Jim makes it sound so simple. The results I now get are fantastic. I have always been able to serve hard but not I have control and easy power.
The best thing is that it applies to all shots. I can whip my slice, flat and topspin shots. You can’t do it on every shot because you get so much power but combine it with deep and up the middle and other shots where power is useful and you will see the results.