Depends on who you are and how much you run. If you're running 50 miles a week, a slow marathon here and there would probably not hurt you too much. I know a gu

Depends on who you are and how much you run. If you're running 50 miles a week, a slow marathon here and there would probably not hurt you too much. I know a guy who used to run a marathon every weekend through the whole season, but I think he ran way more than 50 a week.