One of the things you want to make sure you’re doing when you are serving is getting your core muscles (abs, obliques, lats) into the serve. More generally you want to use as many muscles as possible when you’re serving, but especially the core because it is such a large muscle group. The most effective way to make sure you’re getting your core into your serve is to lead with your front hip into your trophy pose. The way to accomplish getting your front hip out is to imagine that your body should be in a bow shape, with your feet and head behind the baseline but your hip extending out over it. By leading out with the hip like this, it will stretch your core muscles and allow you to pull yourself up and forward into the court, almost like the beginning of a cartwheel motion. If all you do is bend your knees, you won’t get your core into the serve at all. Let’s now take a look at some pros at about 1:05 in the video above. First is Marat Safin, and you can see that he’s leading with his front hip and his body looks like a bow. From this position, he will use his core muscles to pull himself up and out into the court, and that power will be transferred into his swing and the tennis ball. At 1:40, when he is in his racket drop, you can see that he has now straightened his body out and used those muscles. If you look at the two split-screened, you can see the dramatic difference in body position that getting your core muscles into the serve causes.