Biomechanics · functional reading

Center of mass

The center of mass is the point at which the total mass of the body can be considered to be concentrated. It moves with every change of position; in the Earth's gravitational field, it coincides in practice with the center of gravity.

Scientific basis

Its position depends on the configuration of the body segments: when standing, it lies approximately in front of the second sacral vertebra; it moves as soon as you lean forward, raise an arm or sit down. Balance relies on controlling its vertical projection relative to the base of support.

It should not be confused with the center of pressure, the point of application of the resultant of the support forces, which force platforms measure: it is by moving the center of pressure that the body controls the movements of its center of mass.

Blue Portance / SBNFA™ reading

In the SBNFA™ reading, the center of mass is the reference quantity for balance and for the cone of balance: in a seated position, its movements reflect the adjustments of the trunk, pelvis and hips. There is no "correct" position of the center of mass to aim for.

Contribution to the analysis of sitting

Seating analysis observes the distribution of support, which gives indirect information about the movements of the center of mass; it does not measure it.

Not to be confused with

Center of gravity, the point of application of the resultant of gravitational forces, in practice the same as the center of mass on Earth; center of pressure, the point of application of the support forces, measured with a force platform; base of support, the area bounded by the points of support.

Sources and scope

An established concept in mechanics. The positions given are indicative and vary with body build.