Base of support

Scientific basis

When standing, it is bounded by the outline of both feet; it widens when the feet are spread apart or when a cane is used. For a comparable configuration, enlarging the base of support changes the mechanical margin available before the projection of the center of mass crosses its boundaries.

In sitting, it consists mainly of the sit bones (ischial tuberosities), the thighs and the feet, and extends to a backrest or armrests when they are used. The term support polygon is also used: some authors use the two expressions for the same thing, while others reserve “base” for the contact areas and “polygon” for the area they enclose.

Blue Portance / SBNFA™ reading

Together with the center of mass, the base of support defines the mechanical conditions of seated balance. In the SBNFA™ reading, its variations (foot support, distribution between the two sit bones) contribute to adjustments; a wider base of support is not a goal in itself.

Contribution to the analysis of sitting

Seating analysis describes the contact areas, their distribution and their variations over time.

Not to be confused with

Contact area, the zones actually bearing weight; center of mass, the point whose projection must remain within the base of support; support polygon, a term sometimes used for the same area.

Related terms

Center of mass · Cone of balance · Postural balance

Sources and scope

• Winter (1995): balance and posture control in standing and walking (Gait & Posture)
• Horak (2006): postural orientation and equilibrium, the neural control of balance (Age and Ageing)