It may be worth pointing out as well that the stereotypical 40 hour/5 day week applies primarily for people commuting from their homes to a factory/office. There are lots of situations where people commute to a remote location and work ~12 hour days in a week/2 week/month on-off schedule.

Probably not based on scientific study but just a practical response to crews that need to be transported to a remote location and operate 24 hours a day collectively.