I trained for and finished one Ultra (50k road race) on February 23rd '08 as part of my base training miles for Ironman Germany on July 6 '08 (19 weeks apart). In reviewing my training logs for the ultra, about 2/3 of my training hours consisted of outdoor running, with light swimming and indoor spin classes during Dec., Jan, and Feb just to keep the rust off. Since then I have cut back on the running, amped up the swimming and biking, and I still feel like I have good running legs.

I may have done better at the Ultra if I had cut-out the spinning/swimming completely and focussed solely on the run. But since IM Germany is my priority for the entire year, I sacrificed quality at the Ultra, used it just as motivation to train over the winter, and kept swimming and cycling a bit (~2000m swim; ~40miles bike per week) just to keep from losing them completely. At that point, I was in much better run shape than tri shape, so any tri at the time would have been half-assed.

This strategy has worked so far. Other than a less-than-thrilling 6hr finish over 50k of cement, I was able to start the tri season (March) with a solid 400 running miles, and since I kept spinning and swimming, I didn't have to start the swim and bike from scratch. I think Ultras and Tri's can co-exist peacefully. Ultras are (for the most part) cold/cooler month events; Tris are warmer month events. So IMHO, you can easily do Ultras in winter; tri's in summer, but get your efforts worth from the Ultra training and transition to a full IM. If I do an Ultra again, 1) it won't be on cement, and 2) I'll train only for the Ultra.

How many really long runs (over marathon distance) did you guys do to prepare?

Somewhat of a tangent, but I believe in last month's Runner's world, they had a fact or fiction blurb on running surfaces. The claim that hard surfaces cause injury was deemed to be fiction. That seems to be a very black and white answer for such a grey topic. The underlying point is that bad form causes injury ... no kidding. However, proper form comes from learned, repeatable mechanics. Running shoes are designed for support and cushioning over a range of surfaces, the average being something more forgiving than concrete. Therefore, dampening is compromised on concrete, forcing you to alter your stride mechanics. If you develop your stride on concrete and train on concrete, then it's very likely that racing on concrete will have no ill effect. However, if you run on a variety of surfaces, it's very practical to assume that the hard concrete will have adverse effects on your form, thus promoting injury. What would happen to a concrete veteran that decides to go running on the beach? Different foot response, different mechanics, leading to different form. I wouldn't expect a career-ending injury, but probably some fatigue and soreness - indicating that surface response impact the body's response. Just speculation on my part.

Did you mean 20 miles, or 20 minutes? 20 mile walk just seems like it would take too long for me!

Here is another good 50miler training plan (from what I've heard -- I've "only" made it to a 50k so far): http://www.trailrunevents.com/ul/schedule-50m.htm

I've had the itch and I think it needs to be scratched. I've been thinking long and hard about a 50 miler and it just seems like the perfect way to finish out the season.

Is there a site that lists the events?

Ahhh ok... I missed that it was in the part specifically for a 100 miler! I bet you got to see quite a lot of places that way :)

I just did my first 50k when I had planned on doing a 50 miler, and I learned A LOT about what an ultra takes.
My training consisted of my usual tri training, but I dropped one day on the bike for an extra running day.
My weekend run just got a little longer and slower when training for the ultra.
Some interesting things that I noticed while doing the race.
My endurance never suffered I never felt over winded - it was actually my joints that got to me. One thing I wish I would have done more for sure is what Anton said, spend more time in the weight room, it makes all the difference in the world.

Good Luck!

Depends a lot on the race I think. Typically I think a 50k is easier than an IM, but the last 50k I did had 18,000 ft of elevation change and 100+ degree heat index. To me, that was harder than any IM I have ever done. I was only half done with the 50k and I could barely stand up, my urine looked orange, and for the first time ever I wondered how I was going to finish. I did, but it was a death march the last 5 miles. The picture to the left is from that race. I get weak just thinking about it.