Paul, the
mileage isn't much higher than an intermediate to advanced marathon training plan. There are a couple of common differences in how people train for ultras.
- The runs are likely to be slower, and if you're training for a trail event, you'll need to be getting at least your long runs in on trails.
- Eating. Trails are slower, and someone who runs a 3:30 marathon might end up with a 50K time of over 6 hours on a moderate trail course. You can't really do that kind of time on two packets of gu and a swig of gatorade. You need to be able to keep down a sandwich or something and keep on running.
- Back to back runs on weekends. Some people don't do these, but I love them. I'll run 24 on Saturday and then 12 on Sunday. Or vice versa. Also, you wouldn't take a rest day before a long run.
But yeah, totally - on a weekday, six miles is good.
I generally alternate two weeks of about 50-60 miles with one of about 30 miles.