Effects of direction of rotation in continuous and discontinuous 8 hour shift systems

Objectives-Previous research has produced conflicting evidence on the relat ive merits of advancing and delaying shift systems. The current study asses sed the effects of the direction of shift rotation within 8 hour systems, u pon a range of measures including sleep, on shift alertness, physical healt h, and psychological wellbeing. Methods-An abridged version of the standard shiftwork index which included retrospective alertness ratings was completed by four groups of industrial shiftworkers on relatively rapidly rotating 8 hour systems (n=611). Two gro ups worked continuous systems that were either advancing or delaying; the o ther two groups worked discontinuous systems that were either advancing or delaying. Results-Few effects were found of direction of rotation on chronic measures of health and wellbeing, even when the systems incorporated "quick returns " (a break of only 8 hours when changing from one shift to another). This w as despite the use of measures previously shown to be sensitive to the effe cts of a broad range of features of shift systems. However, advancing conti nuous systems seemed to be associated with marginally steeper declines in a lertness across the shift (F (3,1080)=2.87, p<0.05). They were also associa ted with shorter sleeps between morning shifts (F (1,404)=4.01, p<0.05), bu t longer sleeps between afternoons (F (1,424)=4.16, p<0.05). Conclusions-The absence of negative effects of advancing shifts upon the ch ronic outcome measures accorded with previous evidence that advancing shift s may not be as harmful as early research indicated. However, this interpre tation is tempered by the possibility that difficult shift systems self sel ect those workers most able to cope with their deleterious effects. The pre sence of quick returns in advancing continuous systems seemed to impact upo n some of the acute measures such as duration of sleep, although the associ ated effects on alertness seemed to be marginal.