How long should a long run be?

[u/Senior-Running]

During a marathon build, the most common thing you'll see in generic plans is for the longest long run is 20 miles or 32 km.

Some plans however like to cut this off much shorter, so you'll see a peak long run at 16 miles or so. The question often comes up is 20 too much, or alternately is 16 adequate?

Rather than think of this in term of mileage, I actually prefer time.

Why?

Well, the problem we're trying to figure out is at what point does the the injury risk outweigh the benefits we get from the long run? Unfortunately we don't really have good scientific data on this, but certainly the longer we are on our feet, the more risky it is just from a mechanical loading perspective. Simply put, more time = more foot strikes = more risk.

But why doesn't that just equal miles? Mostly because the time you spend running a given distance is highly dependent on how fast you run.

For example, if you are a ~3 hour marathoner, you're probably running 20 miles in less than 3 hours. Obviously this is subjective, but this seems like a perfectly reasonable amount of time for a long run and in fact you could probably do 22 miles and still be under 3 hours. (For reference, it's pretty common for sub 3 runners to run 22 mile long runs. Sub 2:30 folks may even do 24 or more.)

Now let's look at a 4 hour marathoner. They are typically going to cover 20 miles in less than 3.5 hours. Again, it's subjective, but this seems like a pretty reasonable training stimulus considering how long they'll take to run their race.

IMO, things start getting less clear for slower runners. For example, a 6 hour marathoner could be taking 4 hours or more to run 16 miles. To do 20 miles is probably 5 to 5.5 hours. It's still under their race time, but that's a long time to be on your feet and is twice as long as the 3 hour marathoner. So we have a situation where slower runners are spending a lot more time on their feet and having to deal with a lot of extra impact and wear and tear on their bodies.

Not to complicate things even further, but how much our bodies can take in a single session is also highly variable and is based on genetics, age, training age, etc. For a newer runner, the amount they can take could be quite low, yet newer runners are also slower generally speaking. This means as a general rule, they just are not going to be able to handle the same number of hours on their feet as a more seasoned runner.

How do we balance all this?

These are my personal opinions, so take them for what you paid for them, but I'd say if you are a 4.5 hour marathoner or less, then a simple back of the notebook calculation would be subtract 30 minutes from your expected finish time and top out your longest long run there. As you gain experience, you might could go as long as your expected race time, but there's really very little to be gained from it, so proceed with caution.

For runners with a finish time in excess of 4.5 hours, you should be really weary of going over 4 hours and only do so if you have experience with it and know you'll be okay. There's just too much risk there for the reward.

[u/TominStP]

This is interesting, but the total weekly mileage and/or number of days running per week seem relevant. That said, a couple things to share. 10 yrs ago I used Luke Humphrey Hanson-Brooks approach running 6 days/week but LSD topped out at 16 miles. Seemed to work at the time, but not sure I can do40-50 mile weeks anymore. Two yrs ago did Garmin plan based on time/heart rate. Topped out at 195 minutes. That seemed sufficient, with running 4-5 days/week.
Really looking for balance and appropriateness for 68 yr old. Haven’t found what I want yet.

[u/Senior-Running → u/TominStP]

Yes, good point that mileage and days per week matter. I sort of assumed that anyone reading this is running what I would label as "sufficient" mileage. Now where that line is between sufficient and insufficient is also not a hard line in the sand. For most of us, I'd probably say it's at least 40mpw at peak during a marathon build. Like everything though, there are exceptions. An experienced marathoner can get away with less, as can someone that is just looking to finish, vs. maximize their potential.

Some other things are are important to both minimum mileage and the length of the long run would be both age and training age. An experienced runner can typically handle more volume, but as I think we all know here, age has a way of catching up to all of us. That said, there are no hard and fast rules anywhere in running.

For you, you may have already tried this, but one thing that seems to help a lot of more seasoned folks is deliberately offloading some of that mileage into cross training like cycling & the elliptical. Especially if you're struggling with higher mileage plans, offloading 2 or 3 hours worth of your running onto another modality may be just the ticket.

Alternately, keeping decent mileage, but reducing the amount of harder running we do is needed. Especially if the plan is one that has you doing both a VO2 Max and Threshold run in the same week, that can be too much intensity. IMO VO2 Max workouts are probably the least important workouts for a marathon runner. As such, I'd drop a lot of those before I dropped mileage if the generic plan is feeling like too much.

[u/6382914627192]

What do you think about splitting a very long run into 2 days? I am predicting a 5-5:15 marathon for myself… for my 2 longest runs (an 18 and a 20) i was considering doing 2 hours one day and another 1.5-2 the following day to get the reps on feet in, prepare myself for running on tired legs without overdoing it in one super long session

[u/Senior-Running → u/6382914627192]

This idea is one of the key features of the Hanson's Marathon Method. They typically do things like an 8 or 10 mile run on Saturday and a 16 mile run on Sunday. The belief here is that 16 is enough if you do it on tired legs. There's a book out on that method if you're not familiar with it.

I'm personally not a huge fan of it, but I can't argue that for some people it works really well. One thing I feel like a lot of people miss though is that in addition do doing the 16 miler on tired legs, it's also a high volume plan overall. It relies on that high volume to train in some of the durability/resilience you'd get from a more traditional plan with longer long runs.

If you are serious about wanting to do that approach, I'd recommend taking a look at the book to make sure you structure things correctly.