Base of Support Model
Updated: 5.16.26
Hey all!
Today we are discussing a model I use often when teaching a patient WHY they fall or have balance issues. This model is called the Base of Support (BOS) Model, and it does a wonderful job of getting the patient on the same page as the clinician while getting them to buy into the plan of care. It is not the most technical in regards to jargon, so I apologize if any of my healthcare colleagues are watching this. Although I could have written about this model, it is far easier to just do a video on the topic. So that is what I did! Enjoy!
Base of Support Model: Understanding Balance Limits and Fall Risk
Key Takeaways
Balance is governed by a “base of support,” and staying within it determines whether you remain stable or fall.
The body is never perfectly still; small continuous sway is normal and expected in standing balance.
A fall or loss of balance occurs when the body’s center of mass moves beyond the usable base of support without recovery.
Fall risk increases when postural sway becomes larger and moves closer to the boundaries of stability.
Aging-related balance decline is strongly linked to reduced movement, not just biological aging itself.
A more sedentary lifestyle narrows functional balance capacity, reducing the “margin for error” before instability occurs.
Wider stance or altered gait patterns are compensatory strategies to increase the base of support and improve stability.
Balance training works by expanding usable control within the base of support, increasing recovery capacity before a step or fall is required.
Awareness of personal stability limits (your “balance boundary”) improves movement control and reduces unexpected stumbles.
Different foot positions (narrow vs wide stance) significantly change stability demands and fall risk.
Core Explanation
The base of support model simplifies balance into a spatial relationship: your body’s center of mass must remain within the area defined by your feet. Even in quiet standing, the body constantly sways, but healthy balance systems keep that sway well inside safe limits. When sway approaches or crosses the boundary, a step or corrective reaction is required to prevent a fall.
Over time, many people experience a reduction in this “buffer zone.” This is less about sudden dysfunction and more about gradual loss of movement practice, strength, and reactive control. As a result, everyday perturbations begin to push closer to the limits of stability, making stumbles more likely.
Practical Application
This model is useful for understanding why balance declines with inactivity and improves with targeted training. Rather than thinking of balance as simply “good or bad,” it becomes a question of how much usable space you have inside your stability boundary.
Training should focus on expanding control within that boundary, improving the ability to sway, adjust, and recover without stepping. Practically, this can include narrow stance work, controlled weight shifts, and exercises that challenge limits safely. In daily life, it also explains why wider stances feel safer in older adults and why improving reactive stepping ability is critical for fall prevention.
