Abstract
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 link with the diurnal fluctuations of body temperature and vigilance level. Nineteen healthy male 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 and mediolateral directions) indicated that diurnal fluctuations in postural control may occur via changes in the different processes responsible for readjustment via muscle contractions.
Highlights
Various studies reported an influence of time-of-day on postural control [1,2,3,4,5], even if the results were founded on various materials, experimental procedures, and evaluation criteria [6]
Oral temperature, vigilance, and postural sway parameters have been recorded in parallel to specify (i) the link between these parameters and (ii) the role played by vestibular, visual, and somatosensory inputs in the diurnal fluctuations of postural control
The results confirm the presence of diurnal fluctuations in postural control in relation to the increase in body temperature and sleepiness/vigilance levels improvement throughout the day
Summary
Various studies reported an influence of time-of-day on postural control [1,2,3,4,5], even if the results were founded on various materials, experimental procedures, and evaluation criteria [6]. It would be interesting to test the circadian rhythms of other physiological variables such as temperature and vigilance (which are the most studied because of their repercussions on human behaviour [21]) to examine if they evolve to postural control fluctuations This would notably bring further information on possible compensatory adjustments. Since maintaining balance requires continuous integration of different sensory inputs, it has been proposed that vigilance impairment affects the processes of these integrations at the CNS level and, in parallel, affects the processes underlying efficient adjustments of movements involved in postural sway regulation [17, 26, 27]. A frequency analysis applied on centre-of-pressure excursions has been used in the anteroposterior and mediolateral directions
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