Because of my polio arms, I've taken up swimming before work.
Originally, I planned twice a week, but it can be hard work getting up early enough in order to get to the little municipal pool in time. I like this little pool because its also the place where I learned to swim under the stewardship of a Julie Chipchase (fantastic name). After my lessons there, I would always eat these horrible synthetic sour sweets, and later in life, I ended up attending the school next door to the pool. As a theme, sour sweets continue to this day.
I must admit, I do feel the benefit of doing 30 odd lengths (cue jokes about '30 lengths' fnar), but its one of the few things where I am actually competitive, albeit against the old and infirm.
The other people that swim there at that time of morning are generally people in their 40s and 50s but I can't help but swim as fast as I can. The thing that interests me is that usually I am resolutely against competitive behaviour. I don't even like playing computer games. This competition even includes cycling to work - I cannot cycle any other way apart from as fast as I can, and if someone is in front of me I must pass them - a similar thing happens when walking also.
A combination of nervous energy and misanthropy I reckon.