It's called a Marathon RUN for a reason. Running is involved.
Sorry a 6-7 hour Marathon is not really a Marathon run, it's a hike.
And for all these obese people doing it, I would say. Stop it. It's really unhealthy for your joints. You don't get slimmer by "running" you get slimmer by eating less. And eating the right things too. Of course nobody wants to hear it.