We assessed the impact of a common sleep disturbance, the social jetlag, on postural control during a period involving workdays and free days. The sleep habits of 30 healthy subjects were registered with a wrist actimeter for nine days (starting on Friday) and they participated in a set of four postural control tests carried out on Friday and on Monday. In addition, the subjects filled questionnaires about their sleep conditions and preferences. Actimetry measurements were used to calculate the Mid Sleep Phase (MSP). The difference between the MSP values on the workdays and free days measures the social jetlag. There were significant differences in sleep variables between workdays and free days. Postural control performance improved on Monday, after free sleep over the weekend, when compared with the tests performed on Friday. It seems that social jetlag affects brain areas involved in the control of posture, such as thalamus and the prefrontal cortex as well as the cerebellum, resulting in a worse performance in postural control. The performance improvement in the posture tests after the free days could be attributed to a lower sleep debt.

Study design Cross-sectional study. Background Sleep disturbances are frequently reported by individuals with spinal cord injury (SCI) and are associated both with poor quality of life and reduced ability to participate in rehabilitation and daily life activities.Objectives This study investigated sleep quality based on self-reports and actigraphy in individuals with SCI as compared to able-bodied. We also explored the relationship between sleep quality, physical activity, and neuropathic pain. Setting Institute Guttmann, Neurorehabilitation Hospital, Badalona, Barcelona, Spain. Methods Fourteen SCI patients (12 males, 43.10 ± 10.59 y.o.) and 10 healthy individuals (7 males, mean age 46.21 ± 12.58 y.o.) were enrolled in the study. Participants wore wrist actigraphs for 7 consecutive days to characterize their sleep-wake cycle, rest-activity circadian rhythm and physical activity. Sleep quality, chronotype, daytime sleepiness, neuropathic pain severity and interference were assessed based on questionnaires. Results SCI individuals reported poorer sleep quality compared to healthy individuals. Actigraphy-based sleep measurements revealed that patients woke up later, spent more time in bed and slept longer compared to the healthy controls but did not differ significantly in the estimated sleep efficacy and number of awakenings from the able-bodied controls. In individuals with SCI greater physical activity predicted higher sleep efficacy and less awakening episodes as well as shorter sleep latency and lower sleep disturbance. Conclusions The actigraphy-based sleep estimates indicate that patients with SCI spent more time in bed and slept longer but their sleep efficacy was similar to able-bodied controls. Maintaining regular physical activity could improve pain control and sleep quality.

Sleep quality analysis is crucial for human health and it is related to duration, rhythm and quality. The goal of this study is to analyze objective assessment of the sleep-wake cycles with actigraphy, subjective questionnaires and their relationship with sleep quality indices. A wearable actigraph registered the sleep habits of 41 healthy subjects for 9 days. Afterwards, the subjects filled two questionnaires about sleep quality (Pittsburgh Sleep Quality Index) and sleepiness (Epworth Sleepiness Scale). The subjects were divided into two groups based on cut-off scores and the actigraphy parameters were compared between groups. Group 1 in ESS and PSQI categorization had less diurnal sleepiness and better sleep quality, respectively, than Group 2. Measurements of regularity (IS), fragmentation (IV), active phase amplitude (M10), rest amplitude (L5), and relative amplitude (RA) were compared between groups. Group 2 had higher L5 values. Parameter L5 (lowest of 5 consecutive hours of activity) was concluded to be relevant to identify the sleep conditions of the subjects.

Different levels of sleep restriction affect human performance in multiple aspects. However, it is unclear how sleep deprivation affects gait control. We applied a paced gait paradigm that included subliminal rhythm changes to analyze the effects of different sleep restriction levels (acute, chronic and control) on performance. Acute sleep deprivation (one night) group exhibited impaired performance in the sensorimotor synchronization gait protocol, such as a decrease in the Period Error between the footfalls and the auditory stimulus as well as missing more frequently the auditory cues. The group with chronic sleep restriction also underperformed when compared to the control group with a tendency to a late footfall with respect to the RAC sound. Our results suggest that partial or total sleep deprivation leads to a decrease in the performance in the sensorimotor control of gait. The superior performance of the chronic sleep group when compared to the acute group suggests that there is a compensatory mechanism that helps to improve motor performance.

BackgroundDifferent types of sound cues have been used to adapt the human gait rhythm. We investigated whether young healthy volunteers followed subliminal metronome rhythm changes during gait.MethodsTwenty-two healthy adults walked at constant speed on a treadmill following a metronome sound cue (period 566 msec). The metronome rhythm was then either increased or decreased, without informing the subjects, at 1 msec increments or decrements to reach, respectively, a low (596 msec) or a high frequency (536 msec) plateaus. After 30 steps at one of these isochronous conditions, the rhythm returned to the original period with decrements or increments of 1 msec. Motion data were recorded with an optical measurement system to determine footfall. The relative phase between sound cue (stimulus) and foot contact (response) were compared.ResultsGait was entrained to the rhythmic auditory stimulus and subjects subconsciously adapted the step time and length to maintain treadmill speed, while following the rhythm changes. In most cases there was a lead error: the foot contact occurred before the sound cue. The mean error or the absolute mean relative phase increased during the isochronous high (536 msec) or low frequencies (596 msec).ConclusionThese results showed that the gait period is strongly “entrained” with the first metronome rhythm while subjects still followed metronome changes with larger error. This suggests two processes: one slow-adapting, supraspinal oscillator with persistence that predicts the foot contact to occur ahead of the stimulus, and a second fast process linked to sensory inputs that adapts to the mismatch between peripheral sensory input (foot contact) and supraspinal sensory input (auditory rhythm).