Abstract
The purpose of the present study was to evaluate the influence of very low ambient illumination and complete darkness on the postural sway of young and elderly adults. Eighteen healthy young participants aged 23.8±1.5 years and 26 community-dwelling elderly aged 69.8±5.6 years were studied. Each participant performed four tests while standing on a force platform in the following conditions: in normal light (215 lx) with open eyes and with closed eyes, in very low illumination (0.25 lx) with open eyes, and in complete darkness with open eyes. The sequences of the tests in the altered visual conditions were determined by random blocs. Postural sway was assessed by means of the force platform measurements. The centre of pressure variables: the medio-lateral and antero-posterior path lengths, mean velocities, sway areas, and fractal dimensions were analysed. Very low illumination resulted in a statistically significant increase in postural sway in both the young and elderly groups compared to normal light, although the increase was significantly smaller than those observed in the eyes closed and complete darkness condition, and no significant effects of illumination on fractal dimensions were detected. The gains of the sways in the very low or no illumination conditions relative to the normal light condition were significantly larger in the group of young participants than in the group of elderly participants (up to 50% and 25%, respectively). However, the response patterns to changes in illumination were similar in the young and elderly participants, with the exception of the short-range fractal dimension of the medio-lateral sway. In conclusion, very low illumination resulted in increased postural sway compared to normal illumination; however, in the closed eye and complete darkness conditions, postural sway was significantly higher than in the very low illumination condition regardless of the age of the participants.
Highlights
The human balance control system depends on important resources, such as cognitive processing, biomechanical constrains, age, and movement strategies [1], and is based on feedback from the somatosensory, vestibular and visual systems
It can be seen that the values for all four of the sway variables in the time domain were significantly higher during the initial experimental conditions in the elderly group than in the younger group
LSD post hoc tests were performed to assess the differences between the four illumination conditions
Summary
The human balance control system depends on important resources, such as cognitive processing, biomechanical constrains, age, and movement strategies [1], and is based on feedback from the somatosensory, vestibular and visual systems. Different functional situations are present in environments with low and very low illumination Such environments are commonly met indoors, for example, in corridors or in bedrooms and bathrooms at night [14]. These areas are considered to present the highest risk of falls for elderly people; it is estimated that approximately 20 to 55 per cent of all falls occur at home at night among the population that is 65 years or older [7,15]. The rate of falls in elderly adults with poor vision is markedly higher than that among the elderly with normal vision [17]
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