In France, we often do work less than 40 hours a week.Less work also means better productivity. There surely is a "balancing point", but if it exist, it is different for every person, and is not constant with the time.
Believe it or not, there is actual research done on this--not that anyone ever pays attention to the results. If I recall correctly, it boils down to something like this:
- Productivity is low for the first 1-3 hours of a day as people get into the swing of things
- Daily productivity mostly goes up, but drops toward the end of the day (possibly because people are consciously "winding down")
- Productivity per worker hour peaks somewhere around a 30-hour week.
- Total sustainable productivity per week peaks at around a 45-hour week.
- Around 50 hours and up, fatigue builds up over time until burnout kicks in. Sustained work weeks of 50 hours are likely to be getting less TOTAL WORK done than sustained 35-hour weeks.
- Work weeks of around 80 hours are sustainable for maybe a week or so before catastrophic loss of total productivity occurs
- Anything much more than 80 hours likely results in immediately LOWER productivity, as fatigued workers make mistakes that take more time to fix than the extra hours provide.
From this, one can conclude that European schedules are more likely to maximize individual productivity (more work per hour), while American schedules are more likely to maximize organizational productivity (more work per person). One can also conclude that any manager who demands sustained work weeks of 50 hours or more is incompetent and a fool; the management equivalent of the kind of programmer who creates so many bugs he provides a net negative productivity to the team.
In practice, actual work hours are lower than they appear; most salaried workers are prone to finding numerous ways to not work while at work, largely because in many office environments physical presence is seen as more important than actual productivity.
I suspect the best balancing point would be something like four 9-hour workdays per week. Longer days to minimize the productivity drain of mornings, but a shorter total work week to allow occasional bursts of extra effort without creating long-term burnout.