As a distance runner myself, it's been much more of a marathon. You trained long and hard because you're committed to getting that acceptance into a PhD program. You can't just run a marathon from nothing. You need a good foundation to finish that marathon, especially endurance, both mental and physical. That means you had to spend a lot of time in the lab/archives doing the research, or go through the GRE vocab for the upteenth time. On the course, Your fluid stations on the course are your friends, professors, family, and colleagues who feed you "feel-good" drinks to help you think positive when things get tough. The hills on the course? Those are your difficult moments (like... rejections), and long stretches are just the waiting parts. Right now, I'm just running straight ahead, not quite sure where the finish line is, or the next turn is. Either you finish or you don't finish, depending how well prepared you are and whether the course was gracious to you.
Anyhow, when I ran the New York City marathon last November, I actually debated whether or not I'd rather run this or work on my applications. I decided the former was better, and then I really enjoyed the marathon! Of course, then afterward I had to face a couple of interviews with professors... and I began wondering if I should run the marathon again...