. Predictive internal models fluctuate in a circadian basis, as do many other physiological parameters. It could be important to take into consideration the time of day in the planning of rehabilitation programs using physical or mental training.

Why are some healthy male shift workers (SWers) overweight [body mass index (BMI) >25 and <30] if not obese (BMI >30)? Seven risk factors potentially causing overweight and obesity were evaluated, namely (1) age, (2) physical/sports activity, (3) length of exposure to shift work (SW), (4) speed of shift rotation, (5) tolerance to SW, (6) internal desynchronization of circadian rhythms and (8) night eating (nocturnal nibbling). "New" as well as "old" data, acquired from longitudinal and individual time series of 5-56 days recording span, were reanalyzed. The data were analyzed from a set of field studies of 67 SWers and 53 non-shift workers (non-SWers). To estimate the respective weight of these factors, a multiple regression analysis (MRA) was used among other statistical tools. A similar age-related increase in BMI was validated (with p < 0.001) in both SWers and non-SWers. However, in SWers, desynchronization of rhythms increases the effect of age on BMI. Length of exposure to SW, tolerance to SW and speed of rotation do not seem to play a role as risk factors. Major effects are likely to relate to a sedentary lifestyle (lack of regular physical or sport activities) (MRA with p < 0.01), as well as, presumably, to a nocturnal nibbling of carbohydrates, which mimics the night eating syndrome.

Hypergravity disrupts the circadian regulation of temperature (Temp) and locomotor activity (Act) mediated through the vestibular otolithic system in mice. In contrast, we do not know whether the anatomical structures associated with vestibular input are crucial for circadian rhythm regulation at 1 G on Earth. In the present study we observed the effects of bilateral vestibular loss (BVL) on the daily rhythms of Temp and Act in semipigmented rats. Our model of vestibular lesion allowed for selective peripheral hair cell degeneration without any other damage. Rats with BVL exhibited a disruption in their daily rhythms (Temp and Act), which were replaced by a main ultradian period ( Ͻ20 h) for 115.8 Ϯ 68.6 h after vestibular lesion compared with rats in the control group. Daily rhythms of Temp and Act in rats with BVL recovered within 1 wk, probably counterbalanced by photic and other nonphotic time cues. No correlation was found between Temp and Act daily rhythms after vestibular lesion in rats with BVL, suggesting a direct influence of vestibular input on the suprachiasmatic nucleus. Our findings support the hypothesis that the vestibular system has an influence on daily rhythm homeostasis in semipigmented rats on Earth, and raise the question of whether daily rhythms might be altered due to vestibular pathology in humans. vestibular system; biological rhythms; temperature; locomotor activity; rats LOCATED IN THE TEMPORAL BONES, the vestibular system is composed of three semicircular canals that encode head rotation velocity and two otolithic macula that encode linear acceleration and gravity force. The vestibular system is primarily involved in gaze stabilization and postural control (23), but its influence has been expanded to autonomic and bone regulation (11,61,63), spatial learning and memory (5, 6, 56), and spatial orientation and perception of gravitational verticality (37). Studies carried out in environments in which gravity is altered have shown evidence of a possible influence of the vestibular system on hypothalamic circadian function in rats (27) and mice (18,46

Ninety-two runners completed the study during a 168 km mountain ultramarathon (MUM). Sleepiness, self-reported sleep duration, and cognitive performance were assessed the day before the race and up to eight checkpoints during the race. Sleepiness was assessed using the Karolinska Sleepiness Scale. Cognitive performance was also assessed using the Digital Symbol Substitution Task (DSST). Runner reported 23.40 ± 22.20 minutes of sleep (mean ± SD) during the race (race time: 29.38 to 46.20 hours). Sleepiness and cognitive performance decrements increased across this race, and this was modulated by time-of-day with higher sleepiness and greater performance decrements occurring during the early morning hours. Runners who slept on the course prior to testing had poorer cognitive performance, which may suggest that naps on the course were taken due to extreme exertion. This study provides evidence that cognitive performance deficits and sleepiness in MUM are sensitive to time into race and time-of-day.

The methodology for analyzing a biological rhythm has already been the subject of much investigation. However, many questions still have no answer, for example, questions such as the periods chosen: fixed or determined. Throughout this article, we suggest a somewhat innovative methodology that makes it possible to define the steps that seem essential to us in the scientific analysis of rhythms. For some time, this methodology has been put into practice in our laboratory in various studies, some of which have given rise to publications. The notion of quality is a new notion that is present in industry and, when applied to sampling, can improve experimentation. In this way, one may judge the degree to which data samples can be explored as well as the degree of validity of the results of exploration. We provide several methods for achieving this. The search for periods is also important. For this, we have various methods but we must be able to determine those that are the most appropriate and reliable in a particular case. We propose spectral methods, two of which are new and complement 'Cosinor' methodology. On the other hand, modelling uses various methods such as those from, for example, periodic trigonometric functions or more complex chaos functions. We are interested in models from the field of regression (the cosine model) and complementary statistical tests that make it possible to validate the proposed model.

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The yurt is the traditional home of the nomadic Turkmen, the Kyrgyz, the Kazakhs, the Uzbeks, the Kalmyks, the Buryats and the Mongolians. As the impact of the western modern world, in terms of technological and behavioural changes, is slower than anywhere else, the use of the yurt is widespread in the Mongolian steppes, where nomadic life has been maintaining its traditional behaviour for at least 800 years. The Mongolian yurt entrance faces south and combines spatial and functional properties. An open circular hole named the "toon" can be found at the centre of the roof. On sunny days, a ray of sunshine revolves around its inner wall. Depending on the season, the light first appears between 5:40 am and 7:40 am and moves around the different inner walls (khana). The sundial enables the nomads to schedule their daily activities such as the herd milking and its processing, the drying of dung for fuel, the prayers and performing fighting games. The angle of the sun's light coming through the toon and lighting a space on the floor by the yurt entrance can vary according to the time of the year. Such clues are used to guess what time it is and which month it is, and thus help the Mongolians decide whether or not to start travelling from summer to winter pastures. The Mongolians pay special attention to the transhumances, seasonal movements based on a specific time, in order to prevent harming the livestock during the harsh Mongolian winter, and to choose the right time to move the yurt. They also pay attention not to offend the spirits of the wind, the earth and the sky. Regarded as the warrant of their ancestors' cultural traditions, nomadic people remain faithful to their heritage and respect their surrounding environment. Thus, the yurt has remained their reference to time in the heart of the Mongolian steppes.

We investigated the circadian synchronization/desynchronization (by field-study assessment of differences in period, τ, of 16 coexisting and well-documented rhythms) of 30 healthy firemen (FM) exposed to irregular, difficult, and stressful nocturnal work hours who demonstrated excellent clinical tolerance (allochronism). Three groups of FM were studied (A = 12 FM on 24-h duty at the fire station; B = 9 FM on 24-h duty at the emergency call center; C = 9 day-shift administrative FM) of mostly comparable average age, body mass index, career duration, chronotype-morningness/eveningness, and trait of field dependence/independence. The self-assessed 16 circadian rhythms were (i) physiological ones of sleep-wake (sleep log), activity-rest (actography), body temperature (internal transmitter pill probe), right- and left-hand grip strength (hand dynamometer), systolic and diastolic blood pressure (BP) plus heart rate (ambulatory BP monitoring device); (ii) psychological ones (visual analog self-rating scales) of sleepiness, fatigue, fitness for work, and capacity to cope with aggressive social behavior; and (iii) cognitive ones of eye-hand skill and letter cancellation, entailing performance speed (tasks completed/unit time) and accuracy (errors). Data (4-6 time points/24 h; 2 591 480 values in total) were gathered continuously throughout two 8-d spans, one in winter 2010-2011 and one in summer 2011. Each of the resulting 938 unequal-interval time series was analyzed by a special power spectrum analysis to objectively determine the prominent τ. The desynchronization ratio (DR: number of study variables with τ = 24.0 h/number of study variables × 100) served to ascertain the strength/weakness of each rhythm per individual, group, and season. The field study confirmed, independent of group and season, coexistence of rather strong and weak circadian oscillators. Interindividual differences in DR were detected between groups and seasons (χ(2), correlation tests, analysis of variance [ANOVA]). Moreover, in each group, both in winter and summer, a normal distribution was observed in the number of FM with rhythms with τ = 24.0 h, e.g., ranging from 5/16 (large desynchronization) to 16/16 (no desynchronization). Such a normal distribution with intraindividual stability over time (i.e., seasons) is consistent with the hypothesis of an inherited origin of a differential propensity to circadian desynchronization and which is supported by the distribution of τs in winter and summer following the Dian-Circadian Genetic Model, i.e., with τ = 24.0 h, τ = 24.0 h + n(0.8 h), and τ = 24.0 h - n(0.8 h).