Pronation is a term you’ll here a lot when higher-level tennis players discuss proper serve technique. Pronation is a special type of arm movement that allows you to accelerate your tennis racket through the ball, increasing the amount of power and spin you can generate. All advanced players pronate when they serve, but very few club-level players pronate properly.

Let’s start with a basic explanation of what exactly pronation is. Place your hands out in front of your body and point your palms at each other. Now rotate your forearm and wrist together, as one piece, so that your palms are facing the floor. This simple motion of your arm is pronation; the act of turning your palm to face away from you. If you rotate in the opposite direction so that your palms are facing the ceiling, then you are "supinating" your arm, which is the opposite of pronating.

Another good way to understand the motion of pronation involves your cell phone. Take out your phone and hold it to your ear like you were talking to someone. Pretend that your computer monitor is a person and you want to show them who you are talking to. Without adjusting the position of the phone in your hand, you have to pronate to turn your cell phone screen toward your computer monitor. Now that the cell phone’s screen is facing the monitor, you have to supinate to turn your phone screen back toward you.

Again, to reiterate, this motion requires that you rotate your forearm and wrist together as one piece. Pronation is sometimes referred to as a wrist snap. That is incorrect.

So how do you pronate when serving? First, you need the correct grip. Either a continental or eastern backhand will do. The continental is the most common, and you can find an explanation of the continental grip here. To pronate, you start swinging up at the tennis ball on your serve as if you were trying to hammer a nail into the ball. In other words, you would hit the ball with the side of your racket, the frame. But you don’t want to hit the ball with the edge of your frame, you of course want to hit it with your strings! So just before you make contact with the tennis ball, you need to rotate the racket about 90 degrees to get the strings facing the correct direction. That’s where pronation comes in. Wait until the last second and then pronate as fast as you can to make contact with the tennis ball in the center of your strings.

Now why exactly do you want to pronate? What’s the point? When a high-level player pronates, he’s rotating the racket very, very fast. If the racket were allowed to continue rotating it would spin on its axis at a very high rate of speed. This spinning racket has a lot of rotational energy, just like a spinning figure skater has a lot of rotational energy. When a high-level player pronates and makes contact with the tennis ball that rotational energy is transferred into the ball. That’s what adds power and spin to your serve.