Summary of “No, research does not say that you produce more when working 40 hours per week”

Last week, a debate flared up on twitter on working hours in academia and there was the claim that it is irrational to work over 40 hours as output actually goes down.
Cross-country studies will also often impute the legal work hours to workers in different countries even though these may not correspond to hours worked.
It should also lead us to distrust the anecdotal reports of people who say they work 60 hours per week or those who have impressive CVs and claim to work only 35 hours and take long holidays.
As more hours are worked, one can become tired, and the additional hours start producing less than 15mIF. As we take it to the extreme, our academic becomes so tired, he cannot produce anything at all or even produces negative IF. If you are hiring people by the hour, you want them to work to the point where output/hour is optimized, which is the traditional justification for why companies should have shorter work weeks.
Looking at some empirical work, it does seem that while the point of productivity inflection is just about 40 hours per week, the point of maximum output is above 50 hours/week.
Thus, if you are managing a widget factory, you may not want your workers working more than 40-45 hours for your own selfish reasons.
Anecdotally, it does seem that many people work 40 hours at their main jobs and still engage in either a second lower-paying job or in non-leisure cost-saving activities.
I keep reading/hearing this claim that “Research shows that you shouldn’t work as much” or that “Research shows that 40 hours per week is the best”.

The orginal article.