Several studies report that fatigue, induced by sleep deprivation,
extended wakefulness [10e12], or muscle exertion [13e15], degrades
postural stability. It therefore would not be surprising if
fatigue induced by a full day’s work had a similar effect on posture.
However, available data regarding this issue are inconsistent. Some
studies evaluating the circadian rhythm of postural stability have
found an increase of body sway from morning to afternoon [16e18],
whereas others found no change [19] or even a decrease of body
sway [20,21]. We attribute these discrepancies to the fact that most
circadian studies did not control their participants’ activities
throughout the day; thus, some individuals might have arrived for
afternoon testing fatigued, others with an intermediate vigilance
level, and yet others even animated. To avoid the confounding effect
of different activities during the day, we decided to limit our
study to clerical workers of a single facility, who were engaged in broadly similar tasks during their working hours. To prevent the
influence of extraneous circumstances, we tested our participants
twice at their site of employment, once on arrival in the morning
and once on departure in the afternoon