Edited by Dr. Stefano Casali
Shift work is defined by its continuity, its alternation and its schedules. It arises from the need to guarantee essential services for the entire 24-hour period. Work in shifts, in alternating or successive teams, is said continuous when it takes place every day, including Sundays and holidays, and requires the establishment of a minimum of 4 work teams (3 teams working in 8-hour shifts and one team at rest); it is usually designated as "4 x 8 continuous". Work in shifts, in alternating or successive teams, is said semi-continuous when it is interrupted for weekends and requires the formation of a minimum of 3 teams: «3 x 8 semi-continuous». The shift generally lasts 8 hours and the same time is carried out for a duration that defines the alternation rhythm. In most cases it is 7 days or more rarely 5 days. A last characteristic concerns the times of the start of the shift. For most activities, the starting times are 5 or 6 in the morning, 1 or 2 in the afternoon, 9 or 10 in the evening. More rarely at 4, 12, and 20 (C.N.R. Department of personnel 7/1999; Olson C.M., 1984; Magnavita N., 1992).
In relation to the frequency, the following rhythms can be distinguished: circadian or nictemeral rhythms (nict- night, -emera day) whose frequency is about one cycle every 24 hours (in fact between 20 and 28 hours): alternation between wakefulness and sleep, mid-temperature central temperature cycle. THE Infradian rhythms, whose period is greater than 28 hours: the annual, seasonal, monthly rhythms. THE ultradian rhythms whose period is less than 20 hours. Many factors that affect individual characteristics and social conditions can interact with working conditions and influence adaptation in the short and long term (G. Costa, 1990; G Costa., 1999; Melino C., 1992). not all shift workers have clinically significant symptoms. There is considerable inter-individual variability as regards the ability to react positively to these stressors. The possibility of adapting effectively to alterations, even very significant ones, in one's own rhythms, can be traced back to two orders of factors: extrinsic factors, related to the type of shift work (such as the direction and speed of shift rotation), and intrinsic or subjective factors such as: age, length of service and gender, circadian typology, some personological and psychological characteristics (Proceedings of the 25th Conference, 1996; Magnavita N., 1992). Another element to underline is the quality of the environment, which and plays an equally important role: a supervisory task is easier to perform in a "rich" environment than a "poor" one, the important factors are the lighting level, the sound level, their temporal modulations, the alternation of different types of meaningful stimulation. It is well known that situations where the amount of information has decreased are painful to bear and lead to sleepiness. The alertness is not kept at the same level throughout the waking period, it also obeys a circadian modulation. These falls in alertness can correspond to decreases in the performance of the subject: errors, omission of signals, spontaneously occur, increasing with the duration of work, with monotony, fatigue, absence of breaks, sleep deprivation or overeating. (G. Costa, 1990; Olson CM, 1984) It has therefore been proposed to enrich monotonous tasks, in which the signals are too infrequent, with stimulations unrelated to the task but to which the worker must respond.
Particularly important seems to be physiological adaptability, understood as the ability of each individual to realign, more or less rapidly, the rhythm of the different biological functions, to the variations of the sleep-wake rhythm. Another important individual characteristic is the sudden sleepiness. What characterizes sleepy subjects is the high frequency with which they complain of daytime sleepiness and the ease with which they fall asleep, even when conditions would not allow it. The alert subjects, on the other hand, often complain of insomnia, they fall asleep with difficulty and easily resist sleep. Among the latter, however, there are also those subjects characterized by both good levels of "wakeability" and "sleepability" who, by virtue of their ability to sleep or stay awake on command, should also have the greatest Adaptation to shift work. The two main sources of difficulty for shift workers are the desynchronization of sleep schedules and the desynchronization of meal times. These disorders are the cause of most spontaneous abandonment in the first months of turn (Magnavita, 1992; G Costa, 1990; G Costa., 1999) and must be kept in mind because they betray a bad adaptation.
THE sleep disorders essentially consist in the permanent desynchronization between the circadian rhythms, the phases of activity and rest and social habits. The duration and quality of sleep of shift workers vary according to shift hours and environmental conditions. The daytime sleep of night shift workers is shortened by about a third and it is also, albeit to a lesser extent, shortened by workers. of the morning shift, who generally give up going to bed earlier in the evening. The deficit in sleep is implicated not only in the worsening of mental performance and alertness but also among the causes of the feeling of malaise that people complain about. morning shift workers The level of noise to which the sleeper is subjected essentially decreases sleep and the sound environment of rest directly affects the capacity of the worker especially if he is subjected to mental or vigilant effort.
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