The effect of postural threat on the scaling of anticipatory postural adjustments in healthy young adults

Earlier and larger anticipatory postural adjustments (APAs) are generated with increasingly destabilizing movements, such as pulling more forcefully onto a handle, to prevent a loss of balance. The purpose of this study was to determine the influence of postural threat on the ability to scale the magnitude and timing of APAs to increasing amounts of force exertion. Nineteen participants (7 F, 24 ± 2 y, 69.6 ± 9.9 kg, 1.7 ± 0.1 m) pulled on a handle while standing on a surface that was either stationary (No Threat) or that could translate in the medio-lateral direction (Threat). For both conditions, participants completed 36 handle pulls that ranged between 50% and 100% of the participant’s maximal force exertion. For each handle pull trial, APAs were quantified from center of pressure (COP) recordings and electromyographic (EMG) activity of the posterior leg muscles. Results indicated that participants were more physiologically aroused (p=0.013), anxious (p<0.001), and fearful of falling (p