Productivity guy (and regular napper) Merlin Mann's doing some research on Ultradian rhythms, or the recurring cycles our bodies go through during the day – and how a well-placed 20 minute nap can boost your output and morale. An Ultradian rhythm expert says:
When you learn how to recognize your need to take a 20 minute break you can convert your stress into what I call The Ultradian Healing Response – Its that wonderful feeling of comfort and well being that you naturally have when you are tired but let yourself have the freedom to take well deserved rest.
It's not clear how much solid science is behind all this, but I personally work in 1-2 hour sessions with about 20 minues in between which works like a charm for me (versus 4-5 hours of continual work then a crash and burn.) How about you? Got a work and rest rhythm that works for you? Let us know in the comments or to tips at lifehacker.com.