[ghostfish]

The studies referenced in the article you linked refer to the construction industry, not knowledge workers. I would expect anyone producing widgets or physically fabricating things would continue to produce more simply by spending more hours on the job. The question relevant in the original article, and to most of the HN readership, is whether knowledge workers (programmers, engineers, etc.) can get more done by spending more hours at work. I tend to think not, past a certain point, but I'm not entirely where that point is. It certainly depends on what you're doing, culture, work/life balance, hard focus capability and many other factors.

[yummyfajitas]

Very true. We have little good information on this topic, and the original article is wrong - we don't have good evidence that 40 hours is a universal cap.

Most of the data supporting 40 hours/week applies to manufacturing and construction, and is old. Contemporary data (of which there is very little) suggests 60, and again problems of comparing knowledge workers to construction arise.

If someone has good data, I'd love to see it. Until then, stop citing 40 hours/week as peak productivity.