The effect of 24-hour sleep deprivation on postural control in healthy young women and men was studied. It was found that 24-hour sleep deprivation did not adversely affect the posture control of examined women. In men, the results after sleep deprivation showed a deterioration in the open eye test and in the Romberg index. The Romberg index revealed the most statistically significant changes in men (p < 0.05).
Stable posture depends largely on visual stimuli. Our first measurement was conducted in a calm standing position with open eyes. Pham et al. (2014) believe that such a simple test is not enough to expect any changes in postural control after sleep deprivation [24]. However, in other studies [18, 25] and in our own study, this test constituted a reference point for the rest of tests. Usually the average values of open-eye stabilometric parameters are often lower than in other tests. This shows that this measurement is correctly used for comparison with other tests. An increase in the COP path length in the open eye test after sleep deprivation was only recorded in men in the experimental group, and this indicates less stable postural control of men after a sleepless night. The mechanism of change is unclear, but postural stability is strongly associated with lower limb muscle strength [26]. The study conducted by Kujawa et al. (2020) showed that 24 h sleep deprivation reduced lower limb muscle strength in young students [27], and this may have been due to a change in body temperature after 24 h sleep deprivation [28]. This in turn may have resulted in a decrease in muscle function [7]. Postural instability caused by sleep deprivation is probably correlated with this factor. However, these correlations require further studies with EMG.
Visual information may lead to both abnormal postural control of the body and its improvement [29]. In our study, the elimination of visual control resulted in higher COP path length values compared to the open eye study in the experimental and control group. However, based on a literature review [6, 18, 30], postural stability was expected to deteriorate after 24-hour sleep deprivation in the studied students. However, in the closed-eye sample, the COP path length recorded after sleep deprivation did not deteriorate in the experimental group of men and women. Unfortunately, due to the lack of such analyses of stability changes in sleep deprivation according to gender, our observations cannot be confronted with others. It is difficult to explain the reason for the lack of deterioration of body stability after sleep deprivation in the experimental group in this study. It is known that postural control is strongly related to attention processes [30], and cognitive load has an important role in postural control in sleep deprivation [31]. Sleep deprivation impairs cognitive functions and leads to a decrease in regional brain activity. The thalamus and prefrontal cortex regulate cognitive functions such as vigilance and attention. Due to increased sleepiness, tasks requiring more attention become more difficult to perform and require more effort [32]. However, healthy and young people are characterized by better cognitive processes than older people [33], and proper focus of attention can even improve posture control after sleep deprivation [34]. It can be assumed that students, despite the lack of visual control, were able to concentrate in such a way that the lack of sleep did not negatively affect their posture stability. In addition, other studies [35] noted that the subjects were more alert in standing position than sitting after 28 hours of sleep deprivation. The EEG measurement showed that the vertical position increased excitement and allowed them to maintain attention. This may be another aspect explaining the results. In addition, there is a relation between psychological processes and postural control of the body, whereas a reduced mood can have a destabilizing effect on postural control [36]. Thus, there are several different factors that may condition postural control of young people after sleep deprivation.
The Romberg test is used to compare body imbalance in position with open and closed eyes [37]. Many studies have been conducted using this test in conditions after a normal night’s sleep, but only a few studies have used sleep deprivation to test postural control. After sleep deprivation, Ma et al. (2009) did not report significant changes in (male) students’ (Romberg’s) postural control [25]. In another study, Bougard et al. (2019) found that the Romberg index values were higher in the closed-eye test, but did not deteriorate after sleep deprivation.19 In our experiment, the analysis of changes in the Romberg index values showed a higher sensitivity to visual stimuli in the male group than in the female group after sleep deprivation (p < 0.05). This means that men are more sensitive to lack of visual information which affects their less stable body posture. Collins and DeLuca (1995) put forward a hypothesis that the lack of visual stimuli increases the rigidity of musculoskeletal system, which leads to destabilization of postural control [38], and this could be the reason for greater changes in postural stability in the male group. However, further physiological studies between muscle activity and COP displacement are needed to confirm this assumption [39]. Since the obtained Romberg’s coefficient values cannot be referred to any other publication which is based on a similar test procedure, assessing gender differences in detail, further measurements (in other study groups) are needed to confirm the recorded results.
Some papers reported a greater variability in postural stability throughout the day [40], which was still present on the day after the sleep reduction in subjects. However, repeated postural control studies in other papers showed inconsistent results [20]. Due to the postural variability suggested by the above mentioned researchers, depending on the time of day, it is worthwhile to carry out measurements more often during the whole day, especially in the case of healthy people. Our study was conducted in the morning hours and the measurement was conducted only once at each of session. Since other parameters were analyzed at the same time, it would be tiresome and tedious for the subjects to test postural stability several times at two measurement sessions. This could be a factor determining the results obtained in subsequent measurements. It is possible that several measurements of postural control during the day after sleep deprivation would show greater differences between men and women.
In addition, when measuring with open and closed eyes (EO, EC), it was noticed that the mean COP path length results of the control group women between sessions did not deteriorate significantly (p > 0.05). Such a result may indicate differences in the quality of sleep in women. Therefore, sleep quality should be assessed before and during the entire experiment to confirm if the same pattern of changes for EO and EC conditions in each group exists.
Perspectives and significance
There is widespread interest in the study of gender differences in various domains, but sex differences in postural stability is seldom studied. Our results confirm the tendency that women have better postural stability than men. The differences were especially noticeable in the eyes-closed task after sleep deprivation. This could be the result of a number of factors, such as the chronic poor quality of sleep that often characterizes young people. More research are needed to investigate these and other potential correlate factors to confirm these findings.