The long run and more specifically, ending with your longest run a few weeks from race day is one of the most important runs of your preparation for the London marathon. 

Your longest run before tackling the London Marathon puts an end to your final training block and starts off your marathon taper which will allow your body to recover and be fresh for race day.

A lot of runners don’t know how long their longest run should be and more importantly when that longest run should take place….

If those runners were following a London Marathon training plan like this one. They wouldn’t have to worry about making decisions around the long run’s distance, date, and pace, which are already scheduled in the program.

Without following a program it can become quite stressful and confusing which is why we’re going to break down everything you need to know about your longest run before tackling the London Marathon

In this article, we will be covering…

The Importance Of a Long Run In Your London Marathon Training

The purpose of a long run is to achieve several different outcomes, one of the most important outcomes of the long run is to build your endurance to improve your body’s ability to supply oxygen and energy to the working muscles that you will need during the marathon. 

The long run also plays an important role in improving your running economy. Running economy plays a very important role when we are running longer distances. 

Long runs mentally prepare us to be on our feet for a long time, they physically prepare us by strengthening tendons, ligaments, and muscles, and they physiologically prepare us for going longer distances. They also allow us to experiment with different nutrition to find out what works best and what doesn’t work for our stomachs.

The important thing for all of those adaptations to happen is that the long run is not a test of how fast you can go or how fit you are. It is an easy run and should be a social run, you should be able to hold conversations with people.

It’s much harder to take in fuel when you’re struggling to breathe than it is when you’re on a very easy run so you should incorporate a few select long runs with a specific goal purpose in mind where you may run a bit faster and test your race day nutrition, but for the most part, the majority of your long runs are supposed to be very very easy.

One of the biggest changes in physiology to allow the improved delivery of oxygen and energy to working muscles comes from the extension of the capillary network in the working muscles which only happens when we run long.

While there is a minimum distance required to elicit the change in capillary density, there is a point between 20-23 miles, depending on age and small gender variations, that we get diminishing returns. 

Going beyond that point doesn’t allow for any more of those adaptations and causes damage which means the extra miles are not worth the risk.

Even for shorter distances like 5 km or half marathons we still need very high aerobic power to be able to run extremely fast and sustain that speed.

Common Mistakes We See People Making When They Do Their Long Runs 

  1. Running long runs too hard is the biggest mistake that athletes make.
  1. Increasing long runs too quickly week on week.
  1. Stopping too often during the long run. Taking walk breaks is fantastic but stopping at a gas station and stopping your watch for those 30 minutes creates false data. Your average pace looks good, but in a race, you cannot stop your watch when you stop. If you take long breaks, let your watch run so you get a true reflection of the average pace of your long run.

It’s important to note that not all marathon runners are created equal, so their mileage is not going to be the same. What works for one runner might not work for another…

What Determines Your Longest Long Run Time

Your longest run depends on your running experience, your injury risk, and, your goal finish time.

Each marathon training plan will differ from person to person. An 18-mile or 30 km long run will be much less taxing on a sub-3-hour marathon runner compared to a sub-5-hour marathon runner who will probably take almost double the amount of time to complete the 18miles.

That’s why at Coach Parry we plan long runs based on time on your feet rather than the distance that needs to be covered.

If a runner is used to doing long runs or high mileage, then they can likely handle longer long runs. If a runner is a novice or gets frequently injured, then they should increase their long run time requirement to every two weeks instead of every week.

Now that we’ve got why you should definitely be doing long runs out the way, let’s look at the timing of your last long training run before the London Marathon…

When Should Your Last Long Run Be Before The London Marathon?

Too close to race day and you risk arriving on the start line tired. Too far out and you won’t get the full benefit. This answer is primarily based on running ability and experience.

In an ideal world, I suggest novices do their last long run 4 weeks out from the London Marathon race day.

For everyone else, I’d suggest 3 weeks out. 

For the top 5% of the field, that would be the sub-3-hour marathoners it may be slightly closer, again depending on what works best for that individual.  

Now that we know how far out from race day you should do your longest run. Let’s have a look at what pace you should be running your longest run at…

The Pace You Should Be Doing Your Last Long Run At Before The London Marathon

We are not huge fans of extremely long training runs for the following reasons…

As we have mentioned already the length and timing of your long run will be dependent on your race goal and your experience.

Once you have finished your longest training run you are at risk of reaching a point of diminishing returns in that longer runs may prepare you mentally but physically they may do more damage than they are worth and compromise the next few weeks of training and/or race day.

Here’s a comparison according to the Coach Parry plans showing the differences for your longest run leading up to the London Marathon according to your race goal:

(These distances are subject to change according to how well or not well your training leading up to this moment goes.)

Longest Run Distances & Pacing For The London Marathon

Race Goal TimeLongest Run TimePace RangeAmount Of Weeks Before Race Day
Sub 3 Hour3:00 Hours4:25-5:10/km (7:06-8:19 min/mile)3 Weeks
Sub 3.30 Hour3:30 Hours5:15-5:50/km (8:27-9:23 min/mile)3 Weeks
Sub 4 Hour3:15 Hours5:45-6:30/km (9:15-10:28 min/mile)3 Weeks
Sub 4.30 Hour3:30 Hours6:25-7:05/km (10:20-11:24 min/mile)4 Weeks

In conclusion, we want you to realize that London Marathon mileage is dependent on the individual. No two runners will respond the same way to the same amount of mileage. It is so easy to get sucked into the mileage comparison game and we want to urge you not to. 

If you are concerned about the amount of mileage you are doing, it’s better to err on the side of too little than too much.

Follow the Marathon training plan you’ve selected, trust the process, and know that not all the advice you receive is created equal.

Ensure your success with 12 weeks of access to the Coach Parry London Marathon Training Roadmap.
This is a proven, science-based 12-week London Marathon training plan that shows you not only what training to do every day, but exactly what pace that training should be done at so that you avoid injury and ensure you’re not over- or under-trained for come race day.

With that being said, there is always a lot of debate about this topic. Let’s get that out of the way once and for all…

Should You Run 26.2 Miles/42 Kilometers Before Running The London Marathon?

No. As one of South Africa’s most widely recognized running coaches and who has led several teams to the Tokyo Olympic Games as well as the Commonwealth Games … I highly recommend that you should NOT run 26.2 miles before running the London Marathon.

Running 26.2 miles is a huge stress on your body. If you do run that distance before the London Marathon you put yourself at risk for an injury and a bad performance on race day because the chances are high that you will not have time to fully recover.

It’s important to remember that as you reach this stage of your training block, where you need to tackle your longest run, and as the London Marathon draws near… Remember that your training is not about this one single run. It’s about the accumulation of your hard work from when you started your training to the second you cross that start line. 

To help ease the nerves, we put together this article explaining what else you should be doing with four weeks till race day… The Final 4 Weeks Before Race Day


With a passion for high performance sport – Lindsey Parry is one of South Africa’s most widely recognised coaches. Having led a team to the London, Rio and Tokyo Olympic Games as well as the Commonwealth Games in Edinburgh, the Gold Coast & Birmingham, and coached both triathletes and runners onto podiums of some of the world’s most illustrious races, Lindsey has a unique ability to understand what it takes to succeed at any level and thrives on coaching, motivating and inspiring others to do the same – whether it’s on the track, on stage or behind a mic.

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