Peter Knauth

The Effect of Memory Load on the Circadian Variation in Performance Efficiency Under a Rapidly Rotating Shift System

Experimental shift work studios have typically found body temperature and performance efficiency to show very similar circadian rhythms. However, the performance tasks used have placed little, if any, reliance on short term memory. Studies of the variation in performance during the normal waking day have found performance on most tasks to improve over the day but that on short term memory tasks to decrease. The present paper reports an experimental study of the performance of two subjects on a rapidly rotating (-2-2) shift system. Three versions of a now performance test, each with a different memory load, wore administered four times per shift. With the low memory load version, performance showed a high positive correlation with body temperature and was poor during the night shift. However, with the high memory load version, performance was negatively correlated with temperature and was best during the night shift. It is concluded that future shift work studies must take into account the memory load of t...

Duration of sleep depending on the type of shift work

SummaryTime budget studies were performed in eight groups of shift workers. The 9,480 diary records of altogether 1,230 shift workers were analyzed and related to corresponding shift types. The shortest night sleep was found before the morning shift (mean 7.0 h). There were large differences in the duration of day sleep when classifying this sleep into specific types, as day sleep before 1st night shift (mean 2.1 h), between two night shifts (mean 6.1 h), or after last night shift (mean 4.2 h). Average sleep durations of five kinds of day sleep and 12 kinds of night sleep are presented together with 14 frequency distributions of durations of sleep.It is concluded that there should not be many night shifts in succession and that morning shifts should not begin too early to avoid an accumulation of sleep deficits.

Physical training intervention in female shift workers: I. The effects of intervention on fitness, fatigue, sleep, and psychosomatic symptoms

A physical training intervention was carried out on 75 nurses and nursing aides working irregular shifts to determine the effects of such an intervention on health, sleep-wakefulness and adaptation to shiftwork. The study design and changes in physical fitness, fatigue, sleep and psychosomatic symptoms are examined. Training (T) and control (C) groups were built randomly from matched sets of subjects. Questionnaire, laboratory and field studies were done before and after a controlled physical training programme lasting four months. Maximal oxygen consumption and muscle strength increased and heart rates at rest and at work decreased significantly in the T but not in the C group. General fatique during the shift cycle, and fatigue during the night shifts were reduced, whereas fatigue during the evening shifts increased owing to the intervention. Sleep length increased slightly and musculoskeletal symptoms were reduced. The results suggest that moderate physical training increases the physical fitness of fe...

Physical training intervention in female shift workers: II. The effects of intervention on the circadian rhythms of alertness, short-term memory, and body temperature

The effects of a physical training intervention on the circadian rhythms of alertness, short-term memory performance (SAM-test) and oral temperature (t 0) were studied in 75 nurses and nursing aides working irregular shifts in a hospital. Measurements were made every two hours during the days of one morning and two night shifts. In the training group (T), fatigue decreased significantly during the night but not during the day compared to the control group (C). No significant changes were found in the circadian rhythms of the SAM-test and t 0 between the groups, but inside the T group, performance in the SAM-test improved significantly during the day and night shifts, and the mesor and amplitude of t 0 decreased during the day of a morning shift. The results suggest that physical training can induce changes in the circadian rhythms of shift workers which may be interpreted as an adaptation to shift work.

Re-entrainment of body temperature in experimental shift-work studies.

In a series of experimental shift work studies six subjects worked on continuous night shift for three weeks, four subjects worked on a 1-1-1 shift system (1st day morning shift, 2nd day afternoon shift, 3rd day night shift, 4th day off), and two subjects worked on an 2-2-2 shift system (the ‘metropolitan rota’). Rectal temperature was continuously recorded in each experiment. The greatest changes in the circadian rhythm of body temperature occurred on the second night shift day, and during the first week of continuous night shift working. The changes involved both shifts in the phasing of the rhythm, and alterations in its form. The re-entrainment of the rhythm to its normal phasing took two or more days after two or more successive night shifts, but only one day after a single night shift. Considerable individual differences in the rhythm adjustment to night work were observed. In a field validation of these findings, 34 shiftworkers in municipal gas and water supply undertakings measured their oral tem...

Employability and the psychological contract in European ICT sector SMEs

This article explores the employability of information and communication technology (ICT) professionals from the perspective of small- and medium-sized enterprises (SMEs). The first stage of analysis, based on over 100 interviews with managers of ICT supplier companies in seven European countries (Germany, Greece, Italy, the Netherlands, Norway, Poland and the UK), showed most SMEs to have a generally ad hoc approach to managing the employability of their ICT professionals. Assessment and development plans were used primarily to keep skills current to business needs; however, the more developed northern European markets showed greater awareness of the ‘high commitment’ benefits of a more sophisticated approach towards career management (e.g. through mentoring or career planning). A second stage of analysis based only on UK interviews builds on this to propose a model of positive employer influence on psychological contracts through career and employability management practices.

Speed and direction of shift rotation

SUMMARY  This review paper deals with the issue of shift rotation, i.e. the number of consecutive shifts of the same type and the order of change between shifts. To minimize the disturbances of the circadian system and the accumulation of sleep deficits, rapidly and clockwise‐rotating shift systems would seem to be preferable. Regarding consecutive night shifts, a week of night shifts seems to be the worst system with regard to performance and accidents. There is a lack of reliable data on the effects of permanent vs. rotating‐shift systems on alertness, performance and accidents. This is also true for the comparison of forward (delaying) and backward (advancing) rotating‐shift systems, although the former would seem to be associated with fewer problems. For both systems, controlled longitudinal studies are necessary.

Hours of work and shiftwork.

First the time elements of n working day, the duration of working time and the time positioning of working time are treated under ergonomics aspects, Second the reasons for shiftwork, different types of shiftwork as well as effects on health and on family and social life are discussed. Finally the following physiological criteria for optimal shift-schedules are presented: (1) Single night shifts are better than consecutive night shifts. (2) At least 24 hours free time should be allowed after each night shift. (3) The cycle of a shift system should not he too long. (4) The length of the shift should be related to the type of work. (5) In connection with continuous shiftwork as many free weekends as possible should be arranged.

Re-entrainment of body temperature in field studies of shiftwork

SummaryOral temperature readings were taken from six groups of shift-workers (n = 133). The measurements covered a total of 387 days and included readings on a day off and on days of the 1st, 2nd, 4th, 5th and 7th nightshift. The shiftworkers were asked to record oral temperature every 2 h, at work and at leisure, using special thermometers (1°C equals 4 cm). Some of them also interrupted their sleep for additional measurements.On the first day of the night shift the normal circadian rhythm of body temperature was virtually unchanged in most of the groups. However in two groups with a higher physical load during nightwork, an increased temperature was observed during the night (“masking effect”). There were no significant differences between the temperature rhythms in experienced (≥ 15 years of shiftwork) and inexperienced shiftworkers (≤ 1 year of shiftwork) within the first nightshift. During the period of consecutive nightshifts no clear re-entrainment of body temperature was observed. Re-entrainment to nightwork appears to be slower in field studies than in experimental shiftwork studies, which might be explained by the influence of unshifted social “Zeitgebers” in real life.

Memory based performance measures in studies of shiftwork.

The phase of the circadian rhythm in performance efficiency on a given task is known to be influenced by the memory load involved. Two experiments were performed to determine whether memory load also influences the rate at which rhythms adapt to the phase-shifts involved in (a) transmeridian flight and (b) a long period of nightwork. In the first study, high and low memory load versions of a performance test were given to a 25 y old female subject experiencing a 5h eastward change in time-zone. Differences were found both in the initial phase of the two versions of the test and in the rate at which this phase adapted to the new time. In the second study, two young male subjects, working 21 consecutive night shifts, were given high and low memory load versions of the performance test, and a calculations test, every 4 h around the clock. The results were similar to those of the first study: a cosinor analysis revealed that despite periods of arhythmicity there were large differences between the rate of adap...