Under postural threat, which of the following is commonly observed in healthy individuals?

• A. Increased arousal with potential decrease in sway due to muscle co-contraction
• B. Decreased arousal and increased sway
• C. No change in sway or muscle activity
• D. Immediate failure to balance

Answer: (A)

When people feel postural threat, the body tends to enter a state of heightened arousal that prompts a stiffening strategy around the joints. This involves co-activation of opposing muscles (muscle co-contraction), which increases joint stiffness and helps dampen perturbations. The result is a pattern where arousal is elevated and sway is often reduced, as the nervous system uses this co-contraction to stabilize posture quickly and efficiently in the face of threat.

In contrast, decreased arousal would not align with the threat state, increased sway would contradict the stabilizing co-contraction response, and a sudden inability to balance is not typical in healthy individuals under moderate threat.