What defines the base of support in standing balance?

• A. The area bounded by the contact points of the feet with the ground.
• B. The projection of the COM onto the ground.
• C. The line connecting the center of mass to the feet.
• D. The space between the toes.

Answer: (A)

Base of support is the area on the ground that the body’s weight rests on—the region bounded by the outer edges of the surfaces in contact with the ground. In standing, that means the area between and around both feet where they touch the floor. Balance depends on keeping the vertical projection of the body's center of mass inside this boundary; when it moves beyond the edge, tipping toward that side occurs. The projection of the center of mass helps assess stability, but it’s not what defines the base itself. The line from the center of mass to the feet or the space between the toes doesn’t establish the boundary—the boundary is the actual contact-area formed by the feet on the ground.