We spontaneously outstretch our arms when standing upon challenging surfaces, yet theudeffect of stretching the arms upon postural stability is unknown. We investigated whetherudstretching out the arms laterally improves postural control during tandem stance on a narrowudbeam. Twelve healthy participants stood upon a beam, right foot in front of the left foot, forud30 seconds with arms outstretched or down to the side, with eyes open and closed.udMediolateral head movement was characterised by root mean square amplitude (RMS), swayudpath, velocity during the largest excursion and power spectrum. Spectra for lateral forcesudfrom a force platform beneath the beam were also recorded. Outstretching the armsudsignificantly reduced RMS, sway path and velocity of maximum displacement of headudmovement with eyes closed but not with eyes open. A similar trend was present in the powerudspectra of head motion and sway platform lateral forces. In conclusion, outstretching the armsudhelps postural stability in challenging situations such as tandem stance on a narrow beamudwith eyes closed. Although the exact mechanisms require further investigation, the effects areudmost likely mediated by changes in segmental inertia and the ability to make corrective armudmovements.
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