You can emulate what John Gill did without a huge investment in time (though effort is another story). Here's a really short bio and picture from Wikipedia.
This is partially why I'm not very patient with people who give excuses about why they don't make an effort to get into shape. Gill not only was a world-class athlete (performing a one-armed front lever is still thought by some to be nearly impossible), but he was a top-notch mathematician, doing work with linear fractional transformations, something that's well beyond my grasp (I did see a presentation about this at a scientific conference, which provided no illumination). He achieved gymnastic greatness despite being 6' 2" tall and 180 pounds. You don't generally see tall gymnasts.John Gill (born 1937) is an American mathematicianwho has achieved recognition for his rock-climbing. He is considered the Father of Modern Boulderingby many climbers.[1]
Gill basically was a hardcore mathematician with a side-hobby that happened to be physically very demanding. He built a sort of practice arena in his garage to try out new rock-climbing maneuvers. That's a good way of looking at things, rather than fitness being a chore, you can choose to practice a sport (either by yourself or with friends) so it's enjoyable. After a hard day at work, you can crack open a beer, put on some tunes, and start doing something fun almost immediately.
So to the point, how to apply this to yourself. Pavel suggests that whenever you leave the house or enter it, you set up a pullup bar at the door and crank out one or two chinups, every time. Over a period of a day, that could be as many as twenty chinups. Skipping every Sunday is not a problem.
After a few months of consistent effort, you might be uncommonly surprised at your new maximum number of chinups. It's an easy way to get something done without having to set aside a lot of time to do it. It just has to become second nature.
