How does surface stability influence the choice of balance strategy during perturbation?

• A. Firm surface favors the ankle strategy
• B. Firm surface promotes hip or stepping strategies
• C. Foam surfaces promote the ankle strategy
• D. Surface stability has no effect on strategy selection

Answer: (A)

When a person is perturbed, the nervous system chooses a balance strategy based on how stable the base of support is and how big the disturbance is. On a firm, stable surface, small to moderate sways can be controlled mainly through ankle joint actions. The body behaves like a rigid inverted pendulum, and ankle muscles generate torques that shift the center of pressure to counteract sway, keeping the feet in place and correcting quickly with minimal movement higher up the leg. This makes the ankle strategy the efficient and preferred response on a firm surface.

If the perturbation is larger or the surface is unstable or compliant, ankle corrections become less effective, and the body shifts to hip-based actions or even stepping to restore balance by moving the trunk or enlarging the base of support. On foam, sensory input from the feet is reduced and ankle control is less reliable, further favoring hip or stepping strategies.

So, stable surfaces support the ankle strategy for maintaining balance during small perturbations, while instability or larger disturbances push toward hip or stepping strategies.