Why Limit the Long Run to 20%?

You would have run 1:09 on 75MPW.

The way I see it - if your long run puts more stress on you than the fitness you have got to productively absorb it, it will not be productive. You cannot develop the fitness by running just once a week to be able to absorb your long run. So you need to "earn" it in a sense by running adequate mileage more or less evenly spread throughout the week.

So let's say you have been running 3 miles a day 6 days a week, and that is the most you have ever run in your life. If you are not some odd edge case, you will not be able to productively handle anything much longer than 6 miles - though you definitely can go much further, and maybe can even finish the marathon before they close the course. However, if you gradually up your daily mileage to 10, then you would likely benefit from 18-20 mile long runs because you are more fit.

The pitfall I see many runners fall into is they see that they CAN run long, so they do, but they do not ask themselves - is this long of a run actually improving my fitness? I have fallen into that trap myself more than once. In 2003, for example, my fitness got to the point where I could race a full marathon in under 2:30 and not be sore after I finished. Interestingly, I got there with the long runs of only 20 miles. I thought - now I should be able to handle a 26 mile long run in 2:55 with the last 10 miles at 6:00 pace. Not so, it gradually wore me down and I lost the fitness.

What I learned in 34 years of running is that top effort in training often does not produce top results in racing. Rather, a relatively moderate but very consistent effort with occasional pushes to max out the engine very much in moderation is what gives you your best race.

Jaxrunnr wrote:

I keep reading a common training rule that the long run should be no more than 20% of the weekly mileage, usually referencing Daniels (I think) ideology.

This is a terrible rule for 95% of marathoners.

Whether you are aiming to run a marathon is 2:50, 3:00 or for that matter 3:30, you should be doing a 20-miler (at least) most weeks in your marathon build. I don't care if your weekly total is 40mpw, 60mpw, or 80mpw. You need a long run.

Thinking of a 50mpw marathoner, of which there are MANY, I would rather someone run 20/10/10/10 than 10/10/10/10/10??

Obviously one can answer "duhhhh...run more," but realistically unless you are at 100mpw, a necessary long run will be more than 20% of your weekly total.

(Of course, this is different if you are training for shorter distances, where a long run of this duration is less important.)

depends on your goals wrote

I ran 1:12 on 50 mpw...

1:12 is a solid time, so a sincere congratulations

I guess it’s fair to say it depends on your goals, but for me the aim is to be as fast as possible, not to run a specific time and call it good. I haven’t moved up to the half yet, but for a personal example I think I could break 15:00 in the 5000 off of 60mpw. But I try and build up to 80mpw because I don’t want to be just a 14:59 guy.

It just seems strange to me that people are so concerned with the minutia of training like wether you should do 15%, 20%, or 30% for the long run while they miss the bigger picture.

What's wrong with a training that is geared to the individual nature and the personal goals? Some can handle high mileage, some don't. In my point of view the long run should be based on the race distance and play with it. Given a halfmarathon. Sometimes it's necessary to run less but faster, sometimes it's necessary to do a few overdistance runs of 20 miles.

The 20% rule is pretty good.

I see so many runners these days just focusing on that long run on the weekend. They are slow and they get injured a lot. That's at least my observation.

Of course sometimes you can brake this rule to get a longer run in. But in general I think it makes sense.

I will brake myself on your advice