Sure, I believe certain people are built/wired to run certain distances better than others. Look at sprinters vs. distance runners at the elite level. Even 1500m to 10k. A big difference.  Some elite runners move up successfully while others do not. Is it training or genetics or some of both?

Personally I started somewhat late in life to this running thing but even so I always seemed to perform better at half/marathon+ distances then the 5K-10k. Was it my training? Probably, but I can tell you I'd do my intervals and struggled to hit lap splits that others I knew could hit who were in my time range or even slower in the marathon. I always felt something was physically holding me back at high speeds on the track. Probably my V02max.

As for the perfect distance for me, there probably is and never will be one. To say I'm competitive in races would be a joke. Sure, I might have some local AG awards, finished second a time or two at small races, but generally I fell in a certain place on the bell curve in terms of percentage placing at a "normal" sized event. The place on the bell curve is shifting to the right these days as well.

I think when you look at 100 mile runners determining what a quality performance is and whether someone has just trained to finish is a bit judgmental. Sure, there are probably many out there who are not prepared, ready, whatever. I am pretty inexperienced at the 100 mile distance and maybe because I do consider it important to be trained or at least somewhat ready I don't sign up for them very often. A lot of things can go wrong in the 100 mile distance that are not a factor in a 50k or 50miler. You can get by with a few errors in those distances, in the 100 not so much. My last 100, time wise I might have fell into the unprepared category, but had the race ended at 50 miles or 100k it would have been much different story. Mistakes were made earlier in the day that led to issues the next morning. Perhaps that was being unprepared I suppose.

In any case, you can take the argument about runners just being prepared to finish down to the 50m, 50k, and even the marathon these days. It's not just the 100 that it happens. More people running distances. The bell curve shifts. Averages change.

I think it's going to be a combination of innate talent (genetics, fast vs slow twitch, build) and inclination.  

I agree with this.  Through experimentation and experience sooner or later you'll figure out what you are good at and what you like, they may or may not be the same.

With the usual mid-pack disclaimer, I'd say that I seem to do a little better at 100s than marathons or 50k, but that is based on my typical position among the field and compared to some of my friends. Then again less people do 100s so that could account for things as well. Like others have said, I tend to like the challenge of training and finishing the longer distances. I should also say that for me training is more a matter of putting in miles and not a lot of extra stuff like intervals, hills, strength sessions. I do sprinkle them in sometimes, but I tend to just run, which for me is what it's all about, time on the trails and even roads.

I guess that the "challenge aspect" is also why a lot of emphasis is placed on the 100 mile distance.

Good topic lace_up, thanks.

If you are talking about your ideal distance and you use what place you finished (i.e. I finished 4th yea!!), it really is tough to judge accurately dependent on the number of entrants. For example, I once finished 11th place in a trail 25k.  I was very happy about it.  "Almost cracked the top 10", I said.  But there were only 28 runners in the race so it's relative.  Finishing place probably shouldn't be as important as comparisons to your own PRs, how much you had left in the tank, did you run a smart race, possibly ratio of run to walk (depending on the course), negative splits, being able to follow your race plan, being able to adapt when the race plan goes awry, the all important "am I happy with how I ran/raced?", etc.  Many variables...

Interesting nonetheless.

I think it's going to be a combination of innate talent (genetics, fast vs slow twitch, build) and inclination.  If you don't really enjoy running long, you're not going to run long; if you don't like doing intervals you're probably not going to be a 5K specialist.  (But I expect both sides of the equation affect each other, that is, if you're more slow twitch you're going to avoid intervals, self-fulfilling prophecy etc.)

+1 to all of this.

We all tend to lean towards our strengths and preferences.

Looking at field placement, I have had by best successes running shorter trail races (5k,10 mi, 1/2 marathon).  This is probably the distance that my training has allowed me to succeed in.  I don't feel that I've ever really been in 50k shape and I certainly wasn't in 50 mi shape when I ran Stone Mill.  I don't think the average runner really puts in the work to find out if their best distance is something longer than a marathon...it takes a pretty big resume to really know what your optimum distance is.

that's pretty accurate for me; my typical training usually has me in pretty decent shape for 13-20 mile races, I've run four 50k's but I don't think it was necessarily that it wasn't "my distance"- simply training that fell short

it could be "my distance" is 100 miles, but I'll likely never find

I thought about responding to this one awhile ago, but wasn't sure how to respond....

I just looked up my Athlinks profile which has every race I've ever run, and the new site now color codes your times/places from green to red showing how "well" you did in each race, and includes your placing in AG, gender, and overall.

I overwhelmingly perform better in shorter distances, from 5k to the half marathon. In fact, as the distance grows longer, my scores turn from green to red meaning I place further and further back in the pack as the distance grows.

That certainly doesn't mean I enjoy shorter distances more. In fact, I really don't think I enjoy the half marathon distance at all. I will take mid to back of the pack in a marathon or ultra over a higher place in a half any day.

Just an interesting observation.

I want to do a 50 miler and maybe a 100 some day....or at least that is what I say.  My running partner wants to do a 50 miler next year.  So this weekend when I finsihed my 20 miler I was happy to be done.  I asked my partner; do you really want to run 30 more miles?!  If we were doing a 50K we would still have 11 more miles which is doable but 30 seem undoable.  I like 20 miles.  I wish they had more 20 mile races.