Photo: richardmasoner, Flickr

Day 1: Eight o'clock at night, I suddenly realized that I'd completely forgotten to exercise. I'd taken my kids out for a long bike ride earlier in the day -- which is probably why I forgot -- but that doesn't count as exercise for me. My 4-year-old goes slow enough that I do more pedaling backwards than forwards.

Since my bike was still out, I jumped on it for a fast and furious ride that made both my thighs and lungs burn. I was enjoying myself so much, I didn't notice the clouds rolling in and got stuck three miles from home in a downpour. Still, soaked to the skin or not, I tasted the sweet victory of breaking a sweat and reaching my goal for the day.

Thirty minutes isn't hard, and it can even be broken down into several shorter workouts over the course of they day.