Research Article Morning/Evening Differences in Somatosensory Inputs for Postural Control

Copyright © 2014 C. Bougard and D. Davenne.This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The underlying processes responsible for the differences between morning and afternoon measurements of postural control have not yet been clearly identified.This study was conducted to specify the role played by vestibular, visual, and somatosensory inputs in postural balance and their linkwith the diurnal fluctuations of body temperature and vigilance level. Nineteen healthymale subjects (mean age: 20.5 ± 1.3 years) participated in test sessions at 6:00 a.m. and 6:00 p.m. after a normal night’s sleep. Temperature was measured before the subjects completed a sign cancellation test and a postural control evaluation with eyes both open and closed. Our results confirmed that postural control improved throughout the day according to the circadian rhythm of body temperature and sleepiness/vigilance. The path length as a function of surface ratio increased between 6:00 a.m. and 6:00 p.m. This is due to a decrease in the centre-of-pressure surface area, which is associated with an increase in path length. Romberg’s index did not change throughout the day; however, the spectral analysis (fast Fourier transform) of the centre-of-pressure excursions (in anteroposterior andmediolateral directions) indicated that diurnal fluctuations in postural control may occur via changes in the different processes responsible for readjustment via muscle contractions. 1