The threat of a support surface translation affects anticipatory postural control

- The effect of threat on anticipatory postural adjustments (APAs) was examined.
- Postural threat was induced by delivering unpredictable surface translations.
- When postural threat was present, APAs prior to a heel raise became larger.
- Threat also caused larger muscle activity during the execution of a heel raise.
- The effect of threat on APAs depends on the characteristics of the postural threat.

This study examined how postural threat in the form of a potential perturbation affects an individual's ability to perform a heel raise. Seventeen adults completed three conditions: i) low threat, where participants performed a heel raise in response to a “go” tone, ii) high threat, where participants either heard the same “go” tone, for which they performed a heel raise, or experienced a support surface translation in the medio-lateral direction that disturbed their balance, and iii) choice reaction time task, where participants either completed a heel raise in response to the same “go” tone or a toe raise in response to a lower pitched tone. For all heel raise trials, anticipatory postural adjustments (APAs) were quantified from center of pressure (COP) recordings and electromyographic (EMG) activity from the tibialis anterior (TA) and soleus (SOL). Results indicated that participants exhibited larger APAs, as reflected by the greater backward COP displacement (p = 0.038) and velocity (p = 0.022) as well as a larger TA EMG amplitude (p = 0.045), during the high threat condition. During the execution phase of the heel raise, an earlier (p = 0.014) and larger (p = 0.041) SOL EMG activation were observed during the high threat condition. These results contrast with previous findings of reduced APAs when the postural threat was evoked through changes in surface height. Therefore, the characteristics of the postural threat must be considered to isolate the effects of threat on anticipatory movement control.