Center of Mass
The center of mass (COM) is literally the center of the mass of the body. The mass of your body is equally distributed above and below the center of mass, as well as to the right and left, and in front and behind.
If you have ever balanced a golf club on your finger, you have found the center of mass of the club - it was directly above your finger. You probably noticed that your finger was much closer to the club head than the grip. This is because the club head has more mass than the shaft. So to evenly distribute the mass to make sure it doesn’t tilt and fall off, you have to have your finger closer to the club head.
Like the club and shaft, each body part has a certain amount of mass, or weight. For example, each thigh in an average build male is about 14% of the total body weight, while the upper torso accounts for about 30% total body weight. By calculating the mass of each part of the body, we can determine where the middle, or average point, is of all of the mass.
The center of mass is typically slightly above the belly button in a male who is standing upright, and slightly lower in females. This is because males tend to have more mass, in their upper bodies, whereas females tend to have a slightly higher percent of their total body mass in the lower body.
The center of mass is not a fixed location. If a person raises both arms overhead, the mass of the arms has moved higher, so the center of mass moves upward. Using a similar example in golf, as both arms move to the right in the backswing (the trail side of a right-handed golfer), the center of mass also moves to the right.
The following video demonstrates how the center of mass, shown with a blue-green ball, moves during the golf swing.
We will now take a look at how the center of mass moves in a typical good golfer. We'll once again use our blue ball to indicate the center of mass of the golfer. Remember the center of mass shifts as the weight or mass of the body moves. It will move as the mass of the body shifts right to left or up and down.
In the early backswing you can see the center of mass shift away from the target. This is partly caused by the mass of the pelvis and torso moving away from the target but because the arms are moving to the side as well the center of mass will shift farther away from the target than the pelvis. Then as the arms move up you can see the center of mass moves upward as well.
As the downswing begins you can see that the center of mass moves a lot. Now the thighs are moving toward the target, the pelvis is moving toward the target, the torso is moving toward the target and typically around impact we'll see the center of mass right around the back edge of the pelvis. This occurs in most golfers who have the reverse C posture or upper body lean away from the target from impact through early follow through. Once again, the center of mass moves away from the target and up, largely due to the arm's movement, then it moves down and toward the target and finishes there.