From my experience, I find that I am a more productive worker during the stretches during the year when I commute by bike, even though I am probably at work for a little less time per day. I commute by bike two-three times a week during the spring and summer, and not at all during fall and winter. On the days that I ride, I feel invigorated and more focussed. I also know that I have to get my work done, because I typically leave a few minutes earlier to offset the slightly longer commute time home. (It's 70 minutes by bike; 50 minutes by metro.) During the season when I do not ride (or otherwise exercise), I feel sluggish at work.