This is not a novel but a musing, a diary, a philosophy forming; it is based around the running that Murakami does every day. The book is a combination of biography and extended metaphor. Running is used as a metaphor for life, and for writing. Train, persevere, adopt routines, dedicate yourself, learn to do things alone for extended periods: these are all good and noble.
Murakami achieves amazing things with his running. Perhaps he does not feel it when comparing himself to other marathon runners or triathletes, but compared to a normal human for whom a marathon would be impossible (let alone doing one every year) we have to respect the author. He earns it. He is affable and thoughtful, and spending time with his thoughts feels like a privilege and a chance to learn. A good example is from this section towards the end of the book:
"Thus the seasons come and go, and the years pass by. I'll age one more year, and probably finish another novel. One by one, I'll face the tasks before me and complete them as best I can. Focusing on each stride forward, but at the same time taking a long-range view, scanning the scenery as far ahead as I can. I am, after all, a long-distance runner. [...] what's really important is reaching the goal I set myself, under my own power. I give it everything I have, endure what needs enduring, and am able, in my own way, to be satisfied. From out of the failures and joys I always try to come away having grasped a concrete lesson."
I approve of the focus on fitness, and the book left me wanting to run more. That's got to be a good thing.