Why are stepping responses crucial during large perturbations or near the edge of the base of support?

• A. They increase cognitive load and slow responses
• B. They enlarge the base of support and realign the center of mass with the new base
• C. They decrease muscle activation
• D. They are unnecessary if the ankles are stable

Answer: (B)

Stepping responses extend the base of support to keep the body's center of mass within a stable region when a disturbance is large or the person is near the edge of their current stance. When the perturbation is big, ankle strategies (just foot sway) aren’t enough to bring the center of mass back over the feet quickly enough. Taking a step creates a new contact area under the body, enlarging the base of support and repositioning the body so the center of mass falls safely within that expanded base. The step direction typically matches the perturbation, providing a rapid means to decelerate and re-stabilize the torso as the weight shifts onto the new stance.

In contrast, increasing cognitive load wouldn’t improve the physical rapidity and effectiveness of the response, decreasing muscle activation would hinder the necessary leg engagement, and noting that stepping is unnecessary when ankles are stable ignores the limits of stability during large pushes or near the edge of support.