The study investigated the hypothetical differences between male and female shiftworkers in their susceptibility to shiftwork-related health and social problems, with the special reference to the role of the age factor. The comparison concerned two matched-for-age-and-occupation groups of men and women, each of 83 persons, selected from the larger studied population of more than 700 workers in a Polish steel plant. The subjects were crane-operators employed in the same forward-rotated, three-shift, four-team shift system, 4:4:4 with shift changes at 06:00, 14:00, 22:00; and 48 h off following each shift block. The investigation comprised a battery of questionnaires on demographic characteristics, sleep quantity and quality, subjective health complaints, and opinions on shiftwork. The analysis of data revealed that men slept more than women, especially when working on the afternoon and night shifts. The differences became more striking and significant for all work shifts and days-off when related to declared individual sleep requirements. Women experienced more sleep disturbances than men and suffered more frequently from drowsiness during work, especially when working the morning shift. The ratings of subjective health were lower in women, with exception of respiratory complaints. Women generally suffered more than men from symptoms considered as specific to the 'intolerance syndrome', i.e. psychoneurotic, digestive, circulatory, and those of chronic fatigue. However, after passing the 'critical decade' of 40-50 years their subjective health generally improved, whereas in males one observed the consequent deterioration of health with advancing age. Women more often complained about their health and went to see the doctor, but on the other hand, they did not tend to quit shiftwork as often as did their male counterparts.

Time-related accident risk in shift work may be attributed to internal factors, such as fatigue, level of performance, sleep propensity, and to some external factors, like shift system, physical and social environment. Six hundred and sixty-eight events in the metallurgical industry have been analysed in terms of time of day, time on task, consecutive day of the shift block, day of the week, and season. The injury rate was similar on all shifts but more severe accidents happened in the nighttime. Somewhat more injuries occurred in the second half of the shift, in the second part of a shift block, and in summer compared with winter. There were fewer injuries at weekends.

The rates at which the gastric contents are usually passed into the duodenum are much less than the maximal rate which the stomach can achieve. The rates are submaximal because the propulsive mechanism of the stomach is usually partly inhibited through the excitation of duodenal receptors responding to the duodenal contents, recently transferred from the stomach. This being so, mechanical hindrance to the gastric propulsive mechanism might be expected to have little influence on the usual rate of gastric emptying, since the reduced rate of transfer of gastric contents resulting from the hindrance would be offset by the reduced inhibitory action of the duodenal receptors. On the other hand, if a test meal were specially selected to have minimal action on the duodenal receptors, mechanical hindrance of the stomach should significantly slow gastric emptying because there would in this instance be no possibility of reducing the inhibition playing on the stomach.In the experiments described below the stomach was mechanically hindered by tipping supine subjects feet up, head down. The results with test meals which emptied at different rates were consistent with gastric emptying being controlled by duodenal receptors as outlined above. METHODSThe subjects were eight healthy adults of whom seven were medical students. They came to the laboratory without breakfast at about 8 a.m. Their stomachs were washed out through a rubber tube with a 3 mm bore with 250 ml. of tap water at room temperature. After the subjects had taken up their experimental position for the day the meals were instilled into the stomach. The positions were either sitting, or lying supine and horizontal, or lying supine with the whole body tipped to 450 head down on a tilted table. When the meal had been given the tube was occluded until it was used for withdrawing the gastric contents after varying periods on different days. The experimental position was maintained until the gastric contents had been withdrawn and the stomach washed out with 250 ml. of tap water.Three types of meal were used: (a) 750 ml. of 50 mrN trisodium citrate; (b) 750 ml. of 35 mnw hydrochloric acid; (c) 750 ml. of 560 m glucose (100 g./l.). These solutions were chosen in the expectation that they would leave the stomach at different rates, the trisodium citrate solution the most rapidly, (Hunt & Knox 1962), and the glucose solution the most slowly

The interview was carried out with 1664 steelworkers in the aim of obtaining their opinion on subjective fatigue accompanying the work on morning, afternoon and night shifts. Warm and cold seasons of the year were treated separately. Continuous work observations and telemetric heart rate registration were conducted at some workplaces. Analysis of results exhibited a great differentiation of fatigue estimation on particular shifts. Influence of the seasonal factor was found to be very important both in the reported feeling of fatigue as in changes of the pulse rate. Conclusions concern the ergonomic approach to fatigue problems in shift work.