I'm still waiting for Jason
I'm still waiting for Jason to chime in on this one since he has more knowledge and ultras under his belt.
Here's my take having run 1 ultra over 50k - IF you have a base to run a marathon you can certainly run a 50-miler in three months. I did this last year when I ran a marathon on 3/20/11 and ran a 50-miler on 6/11/11 - my mileage over that period averaged a little over 34.31 miles, with the two lowest weeks being the week after the marathon and the week of the ultra (12.05 & 13.44 miles). The longest run during that 11 week period was 17.62 miles. Would I do the same for a 100-miler? Hell no! Although I can say my weekly mileage would be no more than 90-100 miles training for a 100. But, that's just me, and you need to find what works for you.
I'm still waiting for Jason to chime in on this one since he has more knowledge and ultras under his belt.
Here's my take having run 1 ultra over 50k - IF you have a base to run a marathon you can certainly run a 50-miler in three months. I did this last year when I ran a marathon on 3/20/11 and ran a 50-miler on 6/11/11 - my mileage over that period averaged a little over 34.31 miles, with the two lowest weeks being the week after the marathon and the week of the ultra (12.05 & 13.44 miles). The longest run during that 11 week period was 17.62 miles. Would I do the same for a 100-miler? Hell no! Although I can say my weekly mileage would be no more than 90-100 miles training for a 100. But, that's just me, and you need to find what works for you.