The Human Center of Gravity Defined

Center of gravity or mass is the point around which all other parts are equally balanced.
Center of gravity or mass is the point around which all other parts are equally balanced. Brian Hagiwara/Stockbyte/Getty Images

Human center of gravity is a term that has implications for all things related to posture, including issues such as swayback, the design of posture exercise programs and much more.

Gravity is a downward pull, or force, that is exerted by the earth on your body. Your center of gravity is the point around which all parts of your body are balanced.

Believe it or not, your center of gravity can be located outside your body.

How is this possible?

When we define the center of gravity we do so from the reference of a static, standing position. But the body is constantly in motion, which means we change positions often. With each new position comes a new location for the center of gravity. Remember, the COG, as it's sometimes called for short, is the point around which all the parts balance; this may be inside or outside your body. Even slight changes in position can change where your center of gravity is. 

The center of gravity is also called the center of mass. The two terms are interchangeable. 

Center of Gravity Definition — Let's Get Technical

The center of gravity is the average location in a 3-dimensional space, of a person's mass.

Body mass may be understood as the total amount of physical material that comprises your body. Technically, it is your weight divided by the force of gravity. That is, your weight is determined by gravity; if you are on the moon, where gravity is less, you will weigh less, but your mass will remain the same.

But in practical reality, gravity acts on all objects, whether bodies or things, that are located on earth. So as we consider the center of gravity, we remove this force from one side of the equation in an effort to use the most accurate concept and term, which, of course, is mass.

You might also think of mass as your body's resistance to movement, aka, its bulk. On the other hand, your weight is the force that your body's mass exerts when it is — which is all the time for we earthlings — under the influence of gravity.

The Human Center of Gravity

As alluded to earlier, the center of gravity is the point at which the body's mass is equally balanced, and this point changes depending on one's position (arms up/down, leaning, turning a somersault, etc).

Watching dancers, gymnasts and tight-rope walkers offers examples of how, with strength and flexibility training, the human body can change the center of gravity in the most intriguing of fashions, and also how a human being can consciously overcome the effects of gravity and inertia on the body.

When standing, the center of gravity is normally located in front of your sacrum bone, at about the second sacral level. (The sacrum is made up of five bones fused together vertically.)

To understand the difference between theory and practical application, let’s compare the human body to a baseball for a minute. From a point in the exact center, the mass of the baseball is evenly distributed all the way around, is it not? So, with any movement of the ball, this center point moves right along with it. Easy.

But when we consider center of gravity in the human body, things get more complicated. As discussed, because the body has moving parts (arms, legs, head, various areas of the trunk), every time you do, well, anything, the shape of your overall form changes. And if you carry something like a suitcase or grocery bag or if you wear a backpack, this adds weight to some areas, but not others, changing the center of gravity as it does.

So, we can say that the center of gravity is a constantly changing point in or outside the body that represents where the weight or mass of the rest of your body is equally balanced in every direction. This point can and does change based on what you’re carrying and how you’re carrying it, as well as the position you take and the movements you make.

Center of Gravity and Chronic Low Back Pain

Authors of a 2014 study published in the Journal of Back and Musculoskeletal Rehabilitation say that patients with chronic low back pain tend to have center of gravities that are located excessively towards the back. The study found decreased strength in the patients' low backs upon extension, plus decreased amount of normal low back curve. The study authors concluded that people with chronic low back pain whose center of gravities are too far back may have strength and balance challenges to overcome in order to re-establish postural control.