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Cognitive performance is affected by an individual's characteristics and the environment, as well as by the nature of the task and the amount of practice at it. Mental performance tests range in complexity and include subjective estimates of mood, simple objective tests (reaction time), and measures of complex performance that require decisions to be made and priorities set. Mental performance tasks show 2 components, a circadian rhythm and the effects of time awake. The circadian rhythm is in phase with the rhythm of core temperature and there is evidence for a causal link. Increasing time awake results in performance deterioration and is attributed to fatigue. The relative contribution of these 2 components depends upon the task under consideration; simple tasks generally show smaller effects due to increasing time awake. These contributions have been assessed by constant routines and forced desynchronization protocols and have formed the basis of several mathematical models that attempt to predict performance in a variety of field conditions. Mental performance is negatively affected by sleep loss; although short naps are beneficial, sleep inertia limits their value immediately after waking. The processes involved in cognition include attention (tonic and phasic alertness, and selective and sustained attention), working memory (phonological, used for speech, reading, and writing; and visuospatial, used for spatial processing, drawing, and mathematics), and executive function (initiative, decision making, and problem solving). These processes are illuminated by analysis of the regions of the brain involved, the presence of circadian rhythmicity, and the effects of sleep loss. The results from such laboratory- and field-based observations are relevant to the issue of learning in schoolchildren and lead to suggestions for improving their performance.

The influence of prior time awake and time of day on sleep is evaluated in eight male subjects in an isolated sleep laboratory. The subjects were made to sleep for four hours starting at different times of the day. Each sleeping episode is preceded by variable periods of wakefulness. Statistical analysis of the results show the relationships between the parameters under investigation. It is concluded that sleep is affected by both homeostatic and circadian influences.

The present experiment used an intraindividual design to investigate the meaning and measurement of 'good sleep.' Each of 16 subjects slept in an isolation unit according to a schedule (15 sleeps) designed to give variable quality of sleep. Self-rated sleep measures (from the Karolinska Sleep Diary) were obtained after each sleep and subjected to intraindividual regression analyses across time. Most subjective sleep measures showed a strong covariation across conditions. Subjective quality of sleep mainly involved variables of sleep continuity, in particular, perceived calmness of sleep and sleep efficiency. 'Sleep quality,' 'calm sleep,' 'ease of falling asleep,' and ability to 'sleep throughout' the time allotted strongly covaried and formed an index of sleep quality. Self-rated ease of awakening deviated from the general pattern and was associated with poor sleep quality. So was reported dreaming (related to awakenings). It was concluded that most subjective sleep measures tend to covary across conditions and that 'good sleep' is mainly a question of sleep continuity.

The effects of the disturbance of circadian rhythms in shiftworkers' work performance are investigated. Results show that different rates of adjustment to shiftwork hours is found for different types of shiftworkers' tasks, depending on the relative magnitude of their endogenous and exogenous control. Therefore, the design of shift systems must take into account the workers' circadian performance rhythms.

Abstract The amount and timing of sleep and sleep architecture (sleep stages) are determined by several factors, important among which are the environment, circadian rhythms and time awake. Separating the roles played by these factors requires specific protocols, including the constant routine and altered sleep-wake schedules. Results from such protocols have led to the discovery of the factors that determine the amounts and distribution of slow wave and rapid eye movement sleep as well as to the development of models to determine the amount and timing of sleep. One successful model postulates two processes. The first is process S, which is due to sleep pressure (and increases with time awake) and is attributed to a 'sleep homeostat'. Process S reverses during slow wave sleep (when it is called process S'). The second is process C, which shows a daily rhythm that is parallel to the rhythm of core temperature. Processes S and C combine approximately additively to determine the times of sleep onset and waking. The model has proved useful in describing normal sleep in adults. Current work aims to identify the detailed nature of processes S and C. The model can also be applied to circumstances when the sleep-wake cycle is different from the norm in some way. These circumstances include: those who are poor sleepers or short sleepers; the role an individual's chronotype (a measure of how the timing of the individual's preferred sleep-wake cycle compares with the average for a population); and changes in the sleep-wake cycle with age, particularly in adolescence and aging, since individuals tend to prefer to go to sleep later during adolescence and earlier in old age. In all circumstances, the evidence that sleep times and architecture are altered and the possible causes of these changes (including altered S, S' and C processes) are examined.

The objective of the study was to describe the food intake of adventure racers during a competition simulated in the laboratory. Ten male athletes with international experience in adventure races took part in the study. The experiment lasted 67 hr (total distance covered 477.3 km), but 3 athletes did not finish the race. Food intake was recorded throughout the simulation. Athletes' total energy expenditure was greater than their total energy intake (24,516 vs. 14,738 kcal), and the athletes obtained significantly more energy from food than from supplements. Carbohydrate intake was below the recommendation of 0.5-1.0 g · kg-1 · hr-1. These results indicate that guidelines for multiday adventure races are needed. [ABSTRACT FROM AUTHOR]

Studies were conducted to investigate diurnal variations in the accuracy and consistency of the short and long badminton serves and to compare these observations with diurnal variations of temperature and grip strength. It is suggested that some factors that deteriorate during the course of the time spent awake might be involved, in addition to body temperature, in determining accuracy in the tasks measured.

The jet lag syndrome emerged with the rise of long haul air travel. The symptoms Include disturbed sleep, increased fatigue, loss of concentration, and increased irritability during the new daytime, [...]