Abstract
The purpose of this study was to assess properties of vergence and saccade eye movements as well as posture in quiet stance, and the effects of thin plantar inserts upon postural and oculomotor control. The performances of 36 young healthy subjects were recorded by a force platform and an eye tracker in three testing conditions: without plantar stimulation, with a 3 millimetre-thick plantar insert, either a Medial or a Lateral Arch Support (MAS / LAS). The results showed a decrease of the Surface and Variance of Speed and a more posterior position of the CoP with either stimulation compared with the control condition. The fractal analysis showed a decrease with MAS. Wavelet analysis in the time-frequency domain revealed an increase in the Cancelling Time of the low frequency band with MAS. These results suggest a better stability for a lower energy cost. Concerning eye movements, the inserts influenced only vergence (not saccades): MAS caused an increase of the phasic amplitude of divergence, and conversely a decrease of the tonic amplitude. In contrast, LAS caused an increase of the tonic amplitude of convergence. Thus, MAS renders divergence less visually driven, while LAS renders convergence more visually driven. We conclude that the CNS uses the podal signal for both postural and vergence control via specific mechanisms. Plantar inserts have an influence upon posture and vergence movements in a different way according to the part of the foot sole being stimulated. These results can be useful to clinicians interested in foot or eye.
Highlights
Postural control is ensured by a multisensory system wherein eye and foot play an important role [1, 2]
None used thin (< 4mm) specific plantar inserts, which are used by some clinicians in an attempt to improve postural control of PLOS ONE | DOI:10.1371/journal.pone
None of them were taking medication and all of them were asymptomatic and had normal postural performance within the standard stabilometric values of the Association Française de Posturologie (AFP), that is the medio-lateral (X) mean position of the Center of Pressure (CoP) included between -10 and +12 mm, Surface of CoP excursions between 39 and 210 mm2, Variance of speed between 3 and 18 mm2/s2
Summary
Postural control is ensured by a multisensory system wherein eye and foot play an important role [1, 2]. Several studies, summed up in the systematic review from Christovao et al [3], report the effects of different kinds of insoles on balance: vibrating insoles, textured insoles, quick-comfort insoles, insoles with spikes, flat insoles with different hardness, insoles with wedges and sensors and balance-enhancing insoles. None used thin (< 4mm) specific plantar inserts, which are used by some clinicians in an attempt to improve postural control of PLOS ONE | DOI:10.1371/journal.pone.0143693. Controlling Posture and Vergence in Quiet Stance None used thin (< 4mm) specific plantar inserts, which are used by some clinicians in an attempt to improve postural control of PLOS ONE | DOI:10.1371/journal.pone.0143693 December 4, 2015
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