I saw a reference to a study from Stanford University that found that productivity per hour declines sharply when the workweek exceeds 50 hours, and productivity drops off so much after 55 hours that there’s no point in working any more. The article went on to give 10 ways of working less, all of which made good sense (check it out here).Unusually, I checked the source report, and found it was a highly technical study of workers in munitions factories in Britain during World War I. The mathematical analysis made my eyes water, and I wondered whether it was really relevant 100 years later. As I reflected, I thought about how work has changed, and how most of us now do knowledge work rather than manual labour. In that context, the loss of productivity is actually even sharper because the brain on knowledge work is consuming more energy more quickly than when it is working on repetitive tasks.I used to say that if you worked more than 60 hours a week you were a bloody idiot. Now I can say that if you work more than 55 hours a week, you’re wasting your time. And your life.