Base of support is the area enclosed by the outer edges of all body parts, or equipment, in contact with the ground or another supporting surface. In standing it is the region under and between the feet. Adding a hand, a knee, or a walking aid enlarges it.
A person is statically balanced when the vertical projection of the center of mass falls inside the base of support. The closer that projection sits to an edge, the smaller the margin for disturbance before a step, a grab, or a fall becomes necessary.
What Changes the Base of Support
- Foot width and stance width
- Staggered or split stances, which lengthen the base in one direction
- Moving from two feet to one foot, or onto the toes
- Additional contact points such as hands, a racket, or a walking aid
- The size and firmness of the supporting surface
Stability Versus Mobility
A wide base generally makes a position harder to disturb, which is why wrestlers, linemen, and lifters often widen their stance. A narrow base makes it easier to change direction quickly. Many sport skills are a deliberate compromise, and many dynamic movements, such as running and cutting, depend on the center of mass moving outside the base and being caught by the next contact.
Observing It on Video
- A front or rear view shows stance width and side-to-side position of the body over the feet
- A side view shows how far the body sits ahead of or behind the feet
- A camera at roughly hip height and level with the ground reduces distortion of foot positions
- Drawn lines through the feet and a vertical line from the trunk or pelvis can make the relationship easier to see
Limits
The center of mass cannot be seen directly, so video usually relies on an estimate from trunk or pelvis position. Static base-of-support reasoning also applies only partly to fast movements, where momentum matters as much as position. Video can show how a stance is arranged, but it does not on its own explain why someone feels unstable.