which of the following is better (which do you benefit most from and is more exercise?)
two 5 mile runs or one 10 mile run
two 7 mile runs or one 14 mile run
two 3 mile runs or one 6 mile run
AND
three 3 mile runs or one 9 mile run
three 4 mile runs or one 12 mile run
three 5 mile runs or one 15 mile run
you get the point i am trying to put across, so which of the following would be more beneifical to a standard distance runner?
I'm a strong believer in doing singles. I don't do doubles until I hit the 80 mpw mark (which means I haven't done doubles for about 10 months... groan!) Obviously it depends on what you're training for and what your body is better at handling. I'm not an exercise physiologist, so I don't have a great scientific explanation for you, but I've always personally liked putting in longer single runs to increase endurance and then getting a full day of rest before running again. I am, however, out of college, working fulltime, moderately injury prone, and a strength runner (no foot speed). So, my own opinion is do singles. Throw in some doubles once in a while to see if you like them (particularly on workout days). However, don't do triples.
I actually feel like i'm less injury prone doing doubles, which I think I attribute to getting the blood flowing and keeping it flowing moreso than with a whole 22-23 hours between runs, coupled with the supposed susceptibility to injury when your body gets tired, which never has seemed a problem to me. If I hurt myself, it doesn't seem to be at the end of any run. Anyway, that is just from an injury prevention standpoint, but I think I can get my mileage higher doing about 3 doubles a week and i still have plenty of distance runs.
To answer your question directly, I think that considering nothing besides what gives the largest benifit, singles will always be better than doubles or triples accumulating to the same total distance because it is a sustained effort and there is more of a stress / reaction. The reason for doubles seems to be to increase the overall mileage beyond what one would be capable of running only singles. Plus something feels good about getting up in the morning and running what seems short, waking up for the day, and then starting the run in the afternoon feeling like you are already part way done.
my two cents
For aerobic development, on long run is better than two shoter runs.
Agreed, there is more benefit to the single. But if you're just getting back after a layoff, I have found that "sneaky miles" (Like a warmup, then stretch, then a short run, then stretch, then a cooldown) or doubling two short runs that are manageable can speed the comeback. It also allows you to not be writing crap weeks in your log. But once I have the ability, there's no comparison--would much rather do the one run.