Work hard to come up with a good first line, but don't make it scream.
Using the Present Tense I know graduate professors of creative writing who will reject any applicant who sends in an essay written in the present tense.
By the end of the essay, after far too much time in the prison-house of someone else's consciousness, I would be screaming to go for a run myself and would have learned no more about the writer than that he had won/lost/finished the race and that it was hard. It was by a kid who had been a soccer player and used to make fun of the runners with their itty-bitty shorts.
After running a 800m as a freshman, he decided maybe there was something to running after all. When he showed up on campus, I tracked him down and we became friends, meeting for weekly breakfasts at a local diner. When I asked him about why he didn't write about that, he said he didn't want to seem like he was bragging.
Or are you that guy who is always trying something new, and so has shoes that are minimalist, pimped out with LED lights, and bundled up in Gore-Tex?
A look into the closet can be a look into the soul.
There's nothing you can do if the person on whose desk your file lands loves Eagle Scouts and student body presidents and hates poetry and you happen to be an anarchist poet who never goes outdoors.
But that doesn't mean you can't write an essay that will show off who you are and why you would be someone they'd want to meet.
So while running may seem to be the focus, there's got to be something bigger, more universal, and also smaller, more specific, that the essay addresses.
Understanding that an essay has to be about something is hard; figuring out what that aboutness is can be painful. In your closet you have 15 different pairs of running shoes. Are you the girl who is afraid of missing out and who, once she finds something she likes, will stockpile many boxes of the same kind of shoe?