I almost never program exclusively 8 hours in a day. When it does happen, it's either because I'm uniquely inspired -- some insight to a problem that I badly wa

I almost never program exclusively 8 hours in a day. When it does happen, it's either because I'm uniquely inspired -- some insight to a problem that I badly want to resolve -- or there is some crunch deadline approaching fast. Typically I write code in chunks of time not exceeding two hours, after which I shift to other tasks: catching up on emails; writing specs or drawing diagrams; thinking about larger-picture issues; reading work-related documents or instructional material; talking or IMing with coworkers. Also, I take walks, go swimming, go for a run, go to the gym, do some pushups, get a coffee, read a book, play a musical instrument in between programming sessions. Those context shifts make each programming block more meaningful and concentrated for me. My most productive days usually leave me energized, not exhausted.