How many 20 mile long runs should you do in marathon training?

The most common questions that we hear when athletes start a marathon training cycle:

“How many 20 mile runs will I do before the race?”

“I need to run at least ‘X amount’ of 20 milers.”

“I need to run at least 22 miles or else how will I finish 26.2?.”

There is nothing magical about a 20 mile run.
Lets dig deeper…..
The most important thing to consider when training for anything would be individual differences. Every single person is different. Everyone has different natural ability, training experience and goals. You should train specific to your background! Not for someone else. There is such a thing as diminishing returns. That is the point where the training is no longer productive and is actually counter-productive. 

Check Out Our Favorite Fuel For Long Runs:

Benefits of Long Runs

Physiological benefits include :
  • Improved VO2 max
  • Adaptation to utilize fat
  • Increased muscle strength
  • Increased energy stores
Phycological benefit:
  • increased confidence in distance

Individualize Training

Upon starting a marathon training cycle, athletes have a different baseline. The 3 main factors to assess when beginning a program are weekly mileage, long runs, and paces.

Athlete A- 25 miles per week  12:00 pace w/ 8 mile long run (5 hours per week)

Athlete B-  30 miles per week at 10:00 pace w/ 10 mile long run (5 hours per week )

Athlete C- 45 miles per week at 8:00 pace w/ 13 mile long run (6 hours per week)

Athlete D- 80 miles per week at 7:00 pace w/ 18 mile long run (9 hours per week)

Each athlete will have a very different marathon training plan. You need to assess weekly mileage, paces, and long runs as the framework for your marathon training plans. These 3 factors are the most important!

1- Weekly Mileage: The 10% Rule

A widely accepted rule for mileage is to never increase by more than 10%. You never want to start a program that jumps your mileage drastically. Your risk for injuries like stress fractures jumps up with the volume increases. Your health and safety in a program is your number 1 priority. Slow and steady progressive overload wins.
If you are not currently running more than 25-35 miles per week at the start of marathon training, we will have usually increase both mileage AND long runs immediately. The more variables to work on, the more stress we will be putting on your body. The more stress, the more careful we need to be with training!
Athlete A would probably peak around 40 miles for marathon training
Athlete C would probably peak around 55-60s for marathon training
Increasing mileage is all about stress management. Give feedback to your coach and be honest with yourself. There is not a magic mileage number that will get you to XX marathon time.
We have coached athletes to 3:30 marathons who peaked at 38 miles per week and athlete who peaked at 65 miles per week. There is no right or wrong way. The right way is the way your body responds best to!
Potential Signs of ‘too much mileage’:
– Fatigue
– Insomnia
– Constant Heavy Legs
– Inability to hit paces
– Constant desire to do less
– Not improving

2- Long Run Duration: The 3 Hour Rule

Running long is a huge stress on your body. You must balance risk vs. reward. There is a point during a long run around 3-3.5 hours where the damage done actually outweighs the benefits. If you put that strain on your muscles and deplete them of fuel stores it is going to take time to recovery.

Running for 3 hours generally takes days or even a full week to recover completely from.  If every weekend you run 3+ hours and take a week to recover, you are never going to be ready for quality workout during the week.  

If there is too little recovery in between long runs the workouts will suffer. When we pile on too much stress without proper recovery, there will be no physiological benefit.

Runs of over 2 hours are proven to deplete the muscles of energy stores by up to 50%. These energy stores can take close to 72 hours to replenish. Image what a 3 hour run can do. 

Stress + Rest = Growth

There are many quality workouts outside of 20+ mile runs that make for a successful marathon. Steady States, medium long runs, thresholds, tempos, strength workouts, etc. If we focus too much on trying to run for 3+ hours on the weekend, we will not be able to recover on time for the other key workouts in training. We are all about optimizing training for the best results.

Doing too much is when Injuries Happen

Long repetitive bouts of exercise cause micro tears in the muscles the longer you run the more muscular damage you will have. Therefore, the longer you run, the longer it will take to recover.  So if you run too long on Sunday it can set back your entire next week of training. There has to be a balance! 

Physiologically there is not a huge difference between 18 and 20 miles (assuming you are over the 120 minute mark). 20 min could be the difference between getting injured or stay healthy. 
Would 20 minutes of running that could potentially injury you be worth the extra confidence boost?

3- Long Run Volume: The 30% Guideline

 A widely accepted rule is that the long run should not exceed 25-30% of your weekly mileage. That can be difficult if you are running 30 miles a week in a marathon training cycle. That would put your longest long run at 10 miles. In this case you would usually first want to build your overall weekly mileage and then increase the long run as you go. Since there is limited time involved in a training cycle, we will have to be careful which you increase. Risk vs reward.
Long runs are hard on the body. The longer you go the more toll it takes out of your body. The goal is that each week is an accumulation of work. You want your long run to simulate the end of your race- not the beginning of the race! After a week of running and a few quality workouts your legs will be a little fatigued, so the long run makes it a great chance to practice running on tired legs and being mentally strong to complete the distance! 
What we don’t want to happen is for a weekly long run to be 50% of your weekly mileage. Athletes will likely take extra time off to recover from this run only to repeat the cycle the following weekend. We want to focus on the week as a whole not just the Sunday long run.


Another common question:
Why can’t I do all my long runs at marathon pace (MP)?
That is another way to push past that line into overtraining zone.
The faster you run the more muscular damage you cause your body!
If you were to run every long run at marathon pace you are simply delaying your recovery and pushing back the next day that you can get a quality workout in.
Marathon pace is aerobic. Easy running is aerobic. You are stressing the same system to get the same physiological response. Marathon pace is much harder on your body physically, so it increases your risk for potential injuries by running at it ‘all the time’.
For Experienced Runners: It is a great idea to be progressive or to mix in some quicker miles or to finish strong
DO NOT LEAVE YOUR RACE IN A LONG RUN. You do not need to run your long runs at marathon pace to be able to do so on race day. 

Run4PRs approach

We advocate for the long run to be determined by where the individual is in their training. We usually to cap the long run around 3 hours with some exceptions around 3.5 hours max. It will depend on how previous training has been too. A new runner with a previous long run of 60-90 minutes would not want to jump up to run 2.5-3 hours right away. It would be more detrimental that beneficial.
It is also important to remember that training is not written in stone. There is always room for adjustment. If you have a 16 mile run that is a real struggle it doesn’t make sense to run 18 miles just to check it off. It would make more sense to run another 16 mile run and find success. You have to be willing to adapt!
So next time your mailman asks you why you are not running five 20 mile runs at MP so that you can practice it. Just say you are training for YOUR race!!

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