Does outstretching the arms improve postural stability?

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