many people advise against it--but that being said, I did 2 full marathons (one in January and one in May) for the race in August. My longest run after the marathon, 3 weeks out was 22 miles-- and I plan to do similiar this year, with a full marathon in Jan and one in early June.

Pay no attention to BBB! He's psycho! Seriously, his training is not for the average bear.

If you read Daniels' Running Formula (which, IMO anyone who runs should read), you will see that even he only recommends long runs of 2 hours for the most part. But if you have time, you might do 2 of them in a week.

For Ironman training, the keys to running are 1) don't become injured 2) be able to recover from it and 3) do it frequently to develop really strong, "able to run at any time" legs.

The reason you see the 2.5 hour limit is because beyond that, most people need a full day off and probably another day away from any running to recover from it. It's those IM training weekends where people try and do a 112 mile ride one day and then a 3-hour run the next day that can really beat you up unnecessarily.

But if you are a fast runner, you will go pretty far in 2.5 hours, say 18 miles, which is plenty. And you needn't do more than 2 of these runs as long as during your build you are around the 2-hour mark most weeks.

Also read Going Long. Good tips on running there.

The other consideration is that in Ironman, most people are not limited by their sheer ability to run (especially a marathoner), but rather by their muscular endurance on the bike. It takes a lot of hard, focused training to build up the bike muscular endurance to go fast on the bike AND back that up with a good run. Your ability to run in an IM depends, in large part, on your ability to get off the bike with "minimal" fatigue (your IM bike should be one of the easiest rides you do at that distance all year, but if you are a really strong biker you will still be going at a good pace) so that you can express your running ability. It also depends a lot on mental toughness, because an IM is a long time to focus, and no matter who you are, that marathon hurts and your brain doesn't want to do it. So the less tired you start the run, the better off you will be.

That being said, a person needs to decide how much training time to spend at each sport, and by far, biking will need the biggest chunk of time, and so if you are trying to ride 10 hours a week, swim 4 hours and run 5, that's already a 19-hour week, and if that 5 hours of running includes a 3 hour run, then how many other runs are you doing to make the 5 hours and how are you recovering from all that anyway?

So most people find it easier to run more frequently and recover better with a maximum long run of 2-2.5 hours and still have room to fit in enough biking to build that huge engine that will enable them to run well off the bike.

YMMV

Don't get me wrong, I agree too, 2.5 to 3hrs. is long enough but what I am trying to say is that if he wants to run for 4hrs. he can work himself up to that. I don't think there will be any further gains by running 4hrs. but it can be done. I know a few Kona guys that have done a marathon as a training run weeks before the event and it was ok. Hell, it's just 42km! Just make sure you go slow and have plenty of fluids, food and recover well after it. But I agree, there is no ned to do 4hrs. unless you want to.

I think the consensus for the most part is that 2.5 hours. As that seems to be the acceptable time/duration of running that won't break you down too much and allow you to ccontinue with the training.

But most that do perscribe to the 2.5 hour run believe you are getting in 18-22 in that time frame. So, if you are well below that it may be quite a jump in mileage come marathon time.

I did one 3 hour and several 2.5 before Canada. The 3 hour run wasn't that bad as far a breaking me down, and it was a good confidence booster. That said I did walk alot of the marathon - more due to nutrition and probably too much energy on the bike as Kona points out. For next year, I'll focus even more on my cycling and rather than go super long on the runs, I'll focus on getting super comfortable at the 2-2.5 hour range and run more of those during training. Last year I did the one long run Sunday's plan. I'll continue that, but try to add another 2 hour run mid-week.

But, again... This is all suggested training for the average person. A some point the athlete has to learn to read his body and what it can take. I can't take too many long runs at this time. Clearly ultra-runners can and they do run 3+ hour runs on a regular basis. But they aren't swimming and biking.

So, I might just suggest that he work up to a comfortable 18 miles, hopefully that's within the 2.5 hours. If not, maybe focus on getting it there. But 4 hours... seems far too much unless he's very fit and has quick recovery abilities.

I did IMWI (first IM) this year and I did 2 early season marathons. It was solely a mental thing for me as I wanted to know that I could run the distance - as I had never run a marathon before. Even though running an open marathon is not the same as running the marathon in an IM, I just needed to do it. Then after those marathons, I never ran more than 2.5 hours. Also with IMWI being a late season IM, I had plenty of time to recover from the marathons so that it did not interfere with my IM training.