Marathon is the right word! The year after I ran a marathon for the first time, I gave birth at home after 60 hours of labor. The marathon was the best mental training for my birthing experience.
After sharing my birth story with a young woman studying to be an obgyn, she said that a 60 hour labor was impossible! (though common for first time home births) I agreed that it would be impossible in a hospital. Lucky me, I chose the alternative.