baseofsupport

Base of support (BOS) is the area bounded by the parts of the body that are in contact with a supporting surface and provide a base for balance. In biomechanics and related fields, BOS is often represented as the convex polygon formed by the contact points, such as the soles of the feet, though it can include other contact areas in different postures or tasks. The concept is used to understand how posture and movement affect stability.

In static conditions, the BOS is typically the area between and around the feet in contact with the ground. A wider stance increases the BOS and generally improves stability, while a narrow stance or standing on one foot reduces BOS and makes balance more demanding. Dynamic tasks, such as walking or reaching, involve continuous changes to the BOS as different body parts or feet become the new contact points with the surface.

Stability depends on the relationship between the base of support and the body's center of mass (or center of gravity). If the projection of the center of mass falls within the BOS, the body can remain upright without active correction. If the projection moves toward or beyond the boundary of the BOS, balance is challenged, and corrective actions—shifting weight, re-extending posture, or stepping—may be required. The margin of stability is a related measure that quantifies how close the projection is to the BOS boundary.

Applications of BOS analysis appear across rehabilitation, sports science, ergonomics, and robotics. It informs balance training, fall-prevention strategies, assistive device design, and the control algorithms for bipedal robots, all centered on how people and systems manage contact area to maintain upright posture.