The Marathon Training Mistake People Make In Organized 20 Mile Runs


Logo for the Chicago Area Runner’s Association’s annual Ready To Run 20 Miler, held about 3-4 weeks before the annual Chicago Marathon.

In many major cities with major marathons, organizations will hold an official pay-to-play 20 mile run 3-4 weeks before the marathon, to coincide with most participants’ final planned long run before their taper. The official events mark out a course and provide aid stations every 3K or so, much like an actual race.


Though these events are technically held and run like an official race, the clear idea is that participants will do this as their longest training run before the marathon, since most training plans typically ask for runners to peak with a 20 mile long run a few weeks before the race. The idea is not just so runners can do their long run with a like minded group of runners, but that they get support along the way with water and electrolyte sugar fluid every 3K or so, as well as the usual commemorative gear like a bib number and race shirt.

While I totally support the staging and usage of official 20 miler runs for marathon preparation (provided your training plan calls for said 20 mile run), there is a significant mistake most runners make when doing the 20 miler.

The mistake is that runners run the 20 miler at their marathon race pace, basically running it as a race, without considering the consequences of doing so.

Now, making the decision to run the 20 miler at race pace is not necessarily a mistake in itself. In fact, if you’ve been following a quality-long-run plan like Daniels 2Q, 80/20 or Full Potential, where you already do parts of your long run at a faster tempo, this is probably okay.

But most runners typically do their long runs at a slow, easy pace. And whether or not a given runner does so because that’s all they can physically handle… the issue with running the organized 20 miler at marathon pace as a dress rehearsal for the real thing is the undue challenge these runners are adding to an already challenging long run.

Most trainees are not used to running that long AND that hard in this training cycle. Sure, they may have done marathon tempo runs, though often these aren’t more than 10 miles, and they’re done as a stand-alone workout. Sure, you may have run close to 20 miles in training, but you likely did some or all of that run at a much easier pace.

Depending on how you have trained, as well as your training plans for the subsequent taper, you may be pushing yourself far too hard going at race pace for 20 miles.

Be warned: To explain my reasoning I am about to hit you with an avalanche of numbers built around layers of educated assumptions. As long as you heed the basic advice above to take it easy on the 20 miler, you can skip past it all if it bothers you. I’ll re-post the above image below to denote when I’m done talking numbers and ready to explain in more layman’s terms why racing the 20 miler is an issue.

Let’s use the Daniels Running Formula intensity points system to illustrate the difficulty. Using a complex calculus-level formula, Daniels attaches an intensity number to each minute run at a given pace relative to your VDOT, a Daniels-specific VO2max-style statistic to assess your running ability.

I won’t go too far into it because the formulas will give us all headaches and Daniels’ legal team might cease and desist me for doing so anyway. This long but shallow primer however should be sufficient to make my point.

  • As a basic primer, a typical easy run is roughly worth 0.20 intensity points per minute (this of course can vary widely, but I’ll keep it this simple for our example).
  • Your goal marathon pace is worth about 0.45 points per minute (p/m).
  • Running a serious 10K pace might be closer to 0.70 p/m.
  • A 5K pace may be worth 0.85 p/m.
  • An all-out mile time trial might be 1.00 p/m.
  • On the flip side, a super easy recovery jog is often worth 0.10 p/m.

Side note: These relative intensity measurements are often tied to your heart rate and max heart rate, though once many figure out their approximate race paces at all distances they find it easier to use those, looking at heart rates as simply an occasional barometer for how hard or easy they should be working. To keep this all easy to follow I’ll stick to paces as the key variable.

The 5K and 10K numbers are worth noting because they match the intensity of typical speedwork repeats. Lactate threshold, a typical tempo run pace, counts for about 0.65 p/m.

Common approximations are that a grade school runner may average 50-100 points per week. A typical recreational runner who is serious about running races may average 100-120 per week. A hardcore runner who wins age groups in a big city may average closer to 150-175, and a sponsored elite runner who trains all day may net closer to 200 per week.

How many miles is that? It of course depends! The intensity formula is built around the reality that not every mile is equal. One 10K-pace mile is going to demand much more intensity than one easy mile done in a midweek run, and even that may count more than one super easy warm-up mile done before a workout.

Let’s take a rough estimate of running one mile at my current paces for example:

10K pace: 8:45/mile (8.75 min). 8.75 min x 0.70 p/m = 6.13 pts

Regular mile: 10:45/mile (10.75 min). 10.75 min x 0.20 p/m = 2.15 pts

Recovery mile: 12:00/mile. (12.00 min). 12.00 min x 0.10 p/m = 1.20 pts

Even though I ran one mile in all three examples, the effect on me is far different for each example depending on my pace.

Now, how much is too much, or just fine, or not enough?

While, again, that depends, there’s a generally clearer idea on proper limits. Though his book never definitely spells it out, Daniels typically infers that a reasonable expectation for regular workouts is 10-20 points per workout.

Daniels also sets defined percentage limits for speed workouts, though these are tied to more nebulous “tempo”, “interval” and “rep” prescribed intensities, and we’ll skip getting into those specifics for this discussion.

Instead, I’ll focus on total workout intensity and how they illustrate the overall difficulty of a workout.

Let’s say your typical weekday easy run is 60 minutes long.

60 minutes x 0.20 pts/min (p/m) = 12.0 total points

Let’s say I do 8×400 reps at 5K pace once a week, I totally stop to rest between reps, and I begin and end the workout with a 1 mile warmup/cooldown jog.

2 total jog miles x 12:00/mile = 24min –> 24min x 0.10 p/m = 2.4 pts

3200 meters at 5K pace = ~2mi at 5K pace.
5K pace = 8:30/mile (8.5 minutes)

2mi x 8.5min = 17min –> 17min x 0.85 p/m = 14.5 pts

2.4pts jog + 14.5pts speed = 16.9 total points

Notice that even though the workout was shorter, at 41 total active minutes than the 60 minute easy run, the overall intensity was higher.

Let’s say you go for a 2 hour 30 minute (150 minute) long run at regular easy pace.

150 minutes x 0.20 p/m = 30.0 pts

As you’d expect, the long run demands substantially more intensity than the other two workouts due to its overall length.

Question: What if you were to go faster and finish a long workout sooner?

Well, as I mentioned, the 0.20 intensity point estimate is a rough average. Your actual intensity can vary widely depending on how easy or moderate your easy run actually is.

This can generally vary from the aforementioned 0.10 recovery intensity all the way to about 0.40 before it begins to drift into zone 3 long race or tempo intensity, ceasing to be an easy run.

That is still a rather wide range, and if you get into the nuts and bolts you can find that even a second’s difference per mile can move the intensity per minute by about 0.01-0.02 pts per mile. That doesn’t seem like much, but it can add up to about 1 point per hour at easy pace. Run just a few seconds faster on an easy run, and you could increase the difficulty of the run by 30-50%. (Again, the original formula is tied to heart rate, so think of it more so as running a few beats per minute faster than your anticipated easy run)

Short answer: A workout can actually become more intense than anticipated simply if you run it a bit faster than expected, even if the run is still technically easy.

Longer answer by simplified, mildly bastardized example:

5 miles at 10:45 per mile: 5mi x 10.75 min/mile = 53.75min

53.75 min x 0.20 p/m = 10.75pts

Let’s say if I run a more moderate 10:00 per mile, that is worth 0.30 pts/min.

5 miles at 10:00 per mile: 5mi x 10.00 min/mile = 50.00min

50.00min x 0.30 p/m = 15.00pts

The same run, done just under 4 minutes faster, was almost 50% more intense. What was a fairly easy workout had just become a moderately demanding weekday run, even though the distance was the same and the pace was not substantially faster. And that faster pace was not even race pace! It was just a slightly faster easy/moderate pace.

Now, let’s get into races. Daniels gives various recommended limits for tempo, interval and fast rep workouts.

For example, Daniels says individual tempo runs should equal no more than 10% of total weekly volume.

Though ‘volume’ can be determined by mileage or time running, the clear inference is that your reference should be the intensity points. And while ‘weekly volume’ can be determined by that week’s running, it’s implied you should bear in mind the average of the last few weeks as your ‘weekly volume’ frame of reference.

For example, if you average 100 points a week, your tempo paced running shouldn’t total more than 10 points (10% of 100) in a single workout. The idea is simple: If you push for more than that, you risk injury and burnout from the demand of the workout relative to the volume you are taking on.

Throughout the book Daniels also recommends general mile maximums for given intensities, which I won’t get too far into here. If you review the Electric Blues Daniels tables (which I’ve linked before, and can be easily found via Google search), you’ll notice that the tables reference intensity point totals for given mileage distances at key intensities.

You will also notice that the table cuts off at certain mileage points for higher intensities. For example, under the 5K pace there is no reading for any distance beyond 5 miles. Clearly, people typically cannot run beyond that distance safely at that high intensity, an all out race pace for a 3 mile race. The cutoffs trickle down accordingly for subsequent distances up to the Half Marathon, before showing up to 26 miles for the marathon.

Two important points on the recommended marathon intensity:

  1. Unless you are a sub-3:00 marathoner, aka very good/fast, you will see over 100 total intensity points shown on the Electric Blues table for the 26 mile distance.
  2. A large number of experienced runners in various forums have shared the feedback that the Daniels recommended marathon pace was too fast for them to hold for 26.2 miles. In subsequent races they had to follow a slower, more moderate goal pace than the Formula recommended.

If you plug in an elite level 2:15 marathon time to the Electric Blues sheet, you’ll find that said runner could finish the marathon with about 75-80 intensity points. And many such elite runners can in fact hit the recommended paces at all distances.

However, a 4:10 marathon time requires about 115 points of effort. Recall before when I said most runners typically rack up about 100-120 points per week. Such a runner would accrue that much intensity in one marathon at their “race pace”! Is that even do-able?

I would say not, and that would match the anecdotal evidence of such runners who tried to hit the pace and simply could not hold it. And sure, elite runners are running double the weekly volume at 200ish points per week, but because they’re so much faster it also requires a lot less intensity for them to finish a marathon.

And as mentioned, elites can and do build their entire lives around running. They have every resource at their disposal for recovery, and rest most of the entire day in-between workouts. The rest of us have work, families, commitments, lives competing for our free time, and we don’t have those luxuries.

The Daniels Formula, as many running methods are, was designed with elite runners in mind. They can run longer at higher intensities than we can. What may be within reach for them at the marathon distance may be out of reach for others if they go as hard.

While it’s a separate subject, I would posit that a more accurate marathon pace would be slower, slow enough to max out at 100 intensity points, and that such a pace should be your A-goal pace if everything breaks right and you nail everything as expected. Then set a B-goal at 90 intensity points, or a C at 80 and so on. But again, I digress.

Let’s finally go back to the 20 miler, and why running it at marathon pace may not be a good idea.

Take that hypothetical 4:10 goal pace, and extrapolate that over 20 miles. Assume a 9:30/mile pace (slightly faster, but the distance is shorter, you might be excited and feeling good, etc).

9.5 minutes x 20 miles = 190 minutes

190 minutes x 0.45 p/m = 85.5 points

85.5 is a lot of points for a single run. A half marathon for this level of fitness is probably around 70 points. Consider how hard a typical workout is:

  • 10-20 points for regular runs.
  • 20-25 points for speedwork.
  • 30-50 points for typical long runs.

How do you think you’re going to feel after “racing” 20 miles in a workout totaling 85 points, far more than any workout or tune up race you’ve done?


If you raced that 20 miler, you basically just ran a race very close in intensity to a full marathon. And as every marathoner will tell you, it takes weeks, not days, to recover from running a marathon.

You’re three weeks from your goal race, and if you raced that 20 miler you just killed yourself in a very long tune-up race. That not only doesn’t sound like a good idea, you probably also need a few days completely off from training just to recover from the 20 miler. And you’ve got a marathon in three weeks!

Again, do not take this as an indictment of the 20 miler, let alone 20 miler events. Again, I think they’re a good idea. But I think you need to be careful not to “race” them, to run them as full marathon rehearsals. This is hard to do, because everything is dressed up like an actual race with bibs, a fully marked course, aid stations spaced 3K apart, support staff and everything. You almost have to psyche yourself out not to end up racing the 20 miler.

All of this said, consider if instead you ran the 20 miler as a typical easy long run:

20 miles x 10:45 min/mile = 215 minutes

215 minutes x 0.20 p/m = 43.0 points

A 43 point workout is still quite an ass kicker (that’s about as hard as a 12K, 7.45 miles, raced at your absolute best), but it’s far easier to bounce back from that 20 miler than it is to recover from a 20 mile race.

Thus, unless you already mix lots of tempo running into your long runs, I would recommend the following:

Organized 20 Miler Recommendation For Most

If you do a pre-marathon 20 Miler event, I would recommend selecting a corral whose mile or kilometer time is at least 60 seconds slower than your goal pace. You’ll be okay if you run at that pace.

I Already Run Tempo and Marathon Pace In My Long Runs. I’m Fine Racing the 20 Miler.

If you do a lot of mixed tempo long runs, and you absolutely want to treat the 20 miler like a dress rehearsal at race pace, that can still work out fine. Here is what I recommend.

1) For the next three days, either cut your distance in half or take the day off.
2) The next 10 days need to be all easy running. No quality workouts.
3) Eat, sleep, recover hard. Repeat.
4) Just as many would do after the actual marathon, consider seeing a massage therapist. Work out the kinks just as you would do right after the race itself. You basically ARE running a race.
5) If your marathon is two weeks after the 20 miler, this basically means you’re done with quality workouts until the marathon. This WAS your last quality workout.
5a) If your marathon is in three weeks, you will likely have time for perhaps another solid quality workout before the race. Do it as soon after the 10 days as possible, and then don’t do any more. Easy workouts from then until the race.
6) Don’t do a long run longer than a couple hours between now and the marathon. And don’t do one at all within two weeks of the race.

The 20 miler is a great idea in theory, and can be in practice. It’s also a training minefield, and most end up blowing up their entire training plan by jumping in with both feet.

Know and respect your abilities and limits. The harder you go in long runs, the more likely you can handle running the 20 miler at race pace. If like most you do your long runs easy, then proceed with caution. Make sure you also do the 20 miler easy, and don’t fall into the pomp and circumstance trap of running what should be a formal workout like a full-out race.

Make sure you get to marathon race day in the best shape possible to run your best race.

And if the mountain of stats I fed you above seems interesting, absolutely pick up a copy of Daniels Running Formula and learn more about the VDOT formula and the intensity points system.

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