Center of Gravity

Center of Gravity of the human body does not have a constant anatomical location within the body, but moves depending on changes in posture; its excursions relative to the spine can reach 20-25 cm. Experimental determination of the position of the center of gravity of the entire body in a given pose is carried out by one of the following three methods: 1) the subject is placed on a board lying on the sharp edge of a prism, and is moved relative to the latter until unstable equilibrium is achieved on the prism. At this moment, the vertical plane passing through the edge of the prism also passes through the center of gravity of the system (person+board). This (historically oldest) method is tedious and inconvenient. 2) The subject is placed or laid on a board of hanging scales, which are allowed to come to rest in a state of stable equilibrium. In this case, the center of gravity of the system (person+board) lies in the same vertical plane as the axis of suspension of the scales. 3) The subject is laid on a horizontal board resting at both ends on parallel sharp edges of two prisms. One prism has a fixed support, the other is connected to scales that allow determining the pressure it experiences. If we denote the distance between the edges of both prisms as d, the scale reading with an empty board as M₀, their reading with a board with a lying person as M, and the weight of the person as P, then g = d(M-M₀)/P is the horizontal distance from the desired center of gravity of the entire body to the vertical plane passing through the edge of the fixed prism. This method is the most perfect and accurate. The idea of it is attributed to Dubois-Reymond, it was developed and improved by Scheidt and further by N. A. Bernstein. In an upright posture, the center of gravity of the entire human body is located near the upper opening of the pelvis, slightly below the promontory of the sacrum. According to radioscopic observations by M. Ivanitsky, the vertical level of the center of gravity varies from S₁ to S₅. Variations in the position of the center of gravity in the anteroposterior and lateral directions are little studied. Its position along the vertical (cranio-caudal) direction is characterized by an index, in the numerator of which is the vertical distance from the soles of the feet to the center of gravity, and in the denominator is the subject's height. According to Ivanitsky, the center of gravity index usually ranges between 0.555 and 0.565, with individual deviations reaching 0.545 and 0.580. In 1931, Bernstein established on 3 frozen corpses that the positions of the centers of gravity of the long segments of the limbs can be determined on a living person with an error of less than 1 mm by his proposed method of volumetric planimetry, which made it possible to apply the two-board method of Dubois-Reymond to determine the masses of body segments. This author, together with colleagues, conducted extensive research on 152 subjects of both sexes and different ages, the results of which have not yet been fully developed.

The center of gravity of the human body does not have a constant anatomical location within the body, but moves depending on changes in posture; its excursions relative to the spine can reach 20-25 cm. Experimental determination of the position of the center of gravity of the entire body in a given pose is carried out by one of the following three methods: 1) the subject is placed on a board lying on the sharp edge of a prism, and is moved relative to the latter until unstable equilibrium is achieved on the prism. At this moment, the vertical plane passing through the edge of the prism also passes through the center of gravity of the system (person+board). This (historically oldest) method is tedious and inconvenient. 2) The subject is placed or laid on a board of hanging scales, which are allowed to come to rest in a state of stable equilibrium. In this case, the center of gravity of the system (person+board) lies in the same vertical plane as the axis of suspension of the scales. 3) The subject is laid on a horizontal board resting at both ends on parallel sharp edges of two prisms. One prism has a fixed support, the other is connected to scales that allow determining the pressure it experiences. If we denote the distance between the edges of both prisms as d, the scale reading with an empty board as M₀, their reading with a board with a lying person as M, and the weight of the person as P, then g = d(M-M₀)/P is the horizontal distance from the desired center of gravity of the entire body to the vertical plane passing through the edge of the fixed prism. This method is the most perfect and accurate. The idea of it is attributed to Dubois-Reymond, it was developed and improved by Scheidt and further by N. A. Bernstein. In an upright posture, the center of gravity of the entire human body is located near the upper opening of the pelvis, slightly below the promontory of the sacrum. According to radioscopic observations by M. Ivanitsky, the vertical level of the center of gravity varies from S₁ to S₅. Variations in the position of the center of gravity in the anteroposterior and lateral directions are little studied. Its position along the vertical (cranio-caudal) direction is characterized by an index, in the numerator of which is the vertical distance from the soles of the feet to the center of gravity, and in the denominator is the subject's height. According to Ivanitsky, the center of gravity index usually ranges between 0.555 and 0.565, with individual deviations reaching 0.545 and 0.580. In 1931, Bernstein established on 3 frozen corpses that the positions of the centers of gravity of the long segments of the limbs can be determined on a living person with an error of less than 1 mm by his proposed method of volumetric planimetry, which made it possible to apply the two-board method of Dubois-Reymond to determine the masses of body segments. This author, together with colleagues, conducted extensive research on 152 subjects of both sexes and different ages, the results of which have not yet been fully developed.