At the same time as many urban economies are developing into 24-hour societies, it is becoming increasingly popular amongst shift workers to compress their working hours. This is done by working longer shifts and/or restricting free time in-between shifts. The advantage is longer consecutive periods of days off. The disadvantage is lack of recovery during work periods.
John Axelsson has in his thesis at the Department of Psychology at Stockholm University and at the Institute of Psychosocial Medicine evaluated the effects of compressed working hours.
The main aims were to evaluate the effects of long working hours (in the form of 12h shifts) and short recovery periods between shifts (shorter than 16 hours). Another aim was to evaluate possible mechanisms that could suggest why some individuals develop problems with shift work while others do not.
There was no convincing evidence for extended shifts - 12h shifts - inducing more problems with sleep and sleepiness than 8h shifts. The more days off seemed to improve the possibilities to recover properly and counteract possible negative effects of extended shifts, provided the number of consecutive shifts was limited. On the other hand, short recovery times (only 8h) between shifts seriously shortened sleep duration and increased sleepiness. 12h of recovery (between two consecutive 12h shifts) was judged as having no or limited effects on acute measures.