Complexity of Finding the Human Center of Gravity

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 the earth exerts on your body thereby giving you weight. Your center of gravity (COG) is the point about which a body’s weight is equally balanced in all directions.

Believe it or not, your COG can be located outside your body. How is this possible?

When we define the COG, we do so from the reference of a static, standing position. But the body is continuously in motion, which means we change positions often. With each new position comes a new location for the COG. Remember, the center of gravity 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.

Let's Get Technical

The COG 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, your body mass is your weight divided by the force of gravity, and it remains constant no matter what planet you are standing on. That is, body mass is not impacted by gravity while your weight increases and decreases depending on the force of gravity. If you are on the moon, where the force of gravity is one-sixth of the earth's, 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 must 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, and so forth).

Watching dancers, gymnasts and tight-rope walkers offer 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 behind your navel and in front of your sacrum bone, at about the second vertebra level. (The sacrum is made up of five vertebra 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 the 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, 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 continually changing point inside 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.

Chronic Low Back Pain

A 2014 study published in the Journal of Back and Musculoskeletal Rehabilitation found that patients with chronic low back pain tend to have their center of gravity located excessively towards the back.

In the study, patients had decreased low back strength upon extension, plus a decreased amount of normal low back curve. The study authors concluded that those with chronic low back pain whose center of gravity is too far back might have strength and balance challenges to overcome in order to re-establish postural control.