Exercise according to a philosopher

I'm reading a little philosophy. I wasn't a big fan of studying the subject on its own, but lately that's changing. God knows why I started now. That being said, I've taken a liking to Seneca (The Younger) who, according to wikipedia was born in 4 B.C., died 65 A.D. and lived much of his life in Rome. As a Roman Stoic, he lived during a time of the decadent period (good timing). He fashioned gems like

We all sorely complain of the shortness of time, and yet have much more than we know what to do with. Our lives are either spent in doing nothing at all, or in doing nothing to the purpose, or in doing nothing that we ought to do. We are always complaining that our days are few, and acting as though there would be no end of them.

Why only write about running?

Is there some unspoken rule that when you start a blog you are expected to write about a single subject? I have no issue with that sort of dedication, but when the possibilities of topics could be endless it feels self-limiting to pigeonhole yourself by default. It's a personal bias, but I see enough overspecialization in academia as it is. Having said that, grad students tend to be the ones you find most hyper-focused; I feel well-rounded professors should be writing blogs too. So it goes.