Step preparation involves planning where to place the stepping foot; how does perturbation magnitude affect step length?

• A. Larger perturbations require longer steps to reposition the base of support and restore COM alignment.
• B. Larger perturbations require shorter steps to minimize movement.
• C. Step length does not change with perturbation magnitude.
• D. Perturbations only affect stepping timing, not length.

Answer: (A)

When we plan a step after a disturbance, we’re adjusting the stepping foot’s position to expand the base of support quickly enough to re-center the body’s mass above that support. A larger perturbation pushes the center of mass farther from the current base, so to restore stability you need to land the step farther away. A longer step repositions the feet to create a larger support polygon, allowing the center of mass to fall back inside the base and reducing the corrective effort needed from the rest of the body. If the step were short despite a big push, the body wouldn’t regain stable alignment as efficiently, increasing the risk of a fall. So, greater perturbations call for longer steps to reposition the base of support and restore COM alignment.