Can higher working hours reduce productivity? Are there studies about the impact on per-hour output (productivity) of increasing the number of hours worked each week by employees? If every employee works 3hrs/week longer (from 41 to 44hrs), does productivity  increase or decrease?

Edit
About who and how much; if every worker works 3hrs more. So there is more time spent on building machines with the same amount of money. But my hypothesis is, that the more time demotivation overcompensates this marginal plus.
The closest study I could find was that by John Pencavel titled 'The Productivity of Working Hours.'

Abstract:


  Observations on munition workers, most of them women, are organized to examine the relationship between their output and their working hours. The relationship is nonlinear: below an hours threshold, output is proportional to hours; above a threshold, output rises at a decreasing rate as hours increase. Implications of these results for the estimation of labor supply functions are taken up. The findings also link up with current research on the effects of long working hours on accidents and injuries.