The so-called center of gravity is the center of mass symmetry, where the sagittal, frontal and horizontal planes intersect. At this point, the resultant of the gravitational forces that exert their effect on a body is applied.
It should be noted that the center of gravity does not necessarily correspond to a given point of mass on the body. If it is a cube with nothing inside, for example, its center of gravity will not belong to the body.
According to abbreviationfinder, the center of gravity (the geometric point that acts as if it were affected by the resultant of forces external to the system) only agrees with the center of gravity if the gravitational field is uniform by the action of a vector of constant magnitude and direction.
The geometric center or centroid, on the other hand, agrees with the center of mass if the body has uniform density (and therefore is homogeneous) or if the proportion of matter in the system is symmetric.
The human body
In the human body, the center of gravity is in the pelvis, anterior to the sacrum. It is worth mentioning that women have this point lower than men, since their pelvis and thighs weigh more, and that their legs have less extension.
The line of gravity is known as the line that vertically crosses the center of gravity, and that depends on the position of the latter. Roughly speaking, it is correct to say that if the posture is adequate, this line crosses the middle cervical and middle lumbar vertebrae, as well as the front of the dorsal vertebrae.
When walking normally, the center of gravity moves vertically in both directions. The point of greatest height occurs when the limb that carries the weight is in the center of its stance phase; the lowest, on the other hand, occurs when the support is double, that is, when both feet are touching the ground. In a male adult, the midpoint can be said to be approximately 5 cm. During this movement, the line that follows the center of gravity does not change drastically, but is smooth and fluid.
When the weight is transferred between the two legs, the pelvis and trunk deviate laterally, towards the side on which the weight of the body is supported. In addition to the vertical displacement suffered by the center of gravity, it also moves from side to side and the average is again 5 cm. These lateral movements are limited by the average support of each limb. As in the previous case, the curves are not abrupt.
Throughout the stance phase, as soon as the heel makes contact, the knee begins to flex and this continues until it reaches approximately 20 degrees.