I've been a runner all my life, and I've run just a couple sub-40:00 10k's. I have found that I can stay in shape to run a 10k in the low 40's fairly easily; a

I've been a runner all my life, and I've run just a couple sub-40:00 10k's. I have found that I can stay in shape to run a 10k in the low 40's fairly easily; aside from running regularly and eating reasonably, I don't have to work particularly hard at running fast. But as soon as I get in shape to run under 40:00, I have to start paying more attention to sleep. I've pushed myself too hard a number of times, and ended up with bronchitis and pneumonia from not letting my body recover enough. It was always odd to turn in the fastest times in my life just as a serious bronchial infection was taking hold. I have since learned to let a run or two go when I'm feeling tired, and sleep more that day instead. I wish you luck; running is such a great release from technical work, and is often a good source of breakthroughs on technical problems you're trying to figure out.