Sub 4.20 Marathon Goal - How Do I Get There?

by Mark
(UK (Brighton))

Hi, I'm 39 and have been running for nearly 2 years. I have a half marathon and a marathon coming up in the next three months and am looking to beat my PB.

My 5k PB is 25.07, 10k PB 53.03, half 1.58.04 and marathon 5.07 (calf problem at 21km, was on schedule for a 4.40). I'd like to improve my half marathon PB and for the marathon I'd like to get to sub-4:20.

I am 5ft 7in my weight is 13st 7pound and I'm big-built.

I run 25-30 miles a week including a 13mi - 15mi run at the weekends with a bit of mountain biking in between runs.

Can you give me some advice on running sub-9 min miles comfortably.

My first 3 miles are always my worst and in a half marathon miles 8,9 and 10 I can usually run at around 8.30 but slow to 9s there after.

I can run comfortable at 9.30 but would love to run the same at 9s. Any advice would be great. Many thanks.

Answer by Dominique:
Hi there,
Thanks for your question about improving your personal records on both the half and the full marathon.

It sounds like you've made some good progress in your running journey over the past two years. Let's see if we can get you to even better outcomes with a bit of targeted training!

My answer is split as follows:

1. Running time analysis
2. Building your aerobic base
3. Tempo and goal pace runs

Running Time Analysis

I took a look at your race results and plugged them into the Race Conversion Calculator. This tool helps to see if your racing times across different distances are well aligned. Here's what I found:

Your expected 10k time based on your 5k PB (25:07) is more than 30 seconds lower than your actual PB of 53:03.

Your half marathon PB is a minute slower than your current PB, based on your 10k PB time.

Based on your half marathon PB (1:58:04), your predicted marathon time is around 4:20. Based on the shorter distances it is faster, but the longer distances are the better predictors of current ability.

What does this tell us?
Well, two things: firstly, your times are close but not fully aligned. Secondly, you do have the potential to hit a sub-4:20 marathon.

The main limiting factor here seems to be your endurance. You have the basic speed but need to maintain it for longer, which leads us to the next part.

Building Your Aerobic Base

Your long run is really good. A regular 13 mi to 15 mi long run is fantastic. Particularly for the half marathon. And for the marathon it is a great starting point.

But your overall mileage of 25 to 30 miles is a tad low for a great marathon performance. Your aerobic base is crucial for marathon success as it allows you to sustain your speed over longer distances. Improving this means focusing more on long runs and easy runs.

What needs to happen now, in preparation for that marathon in three months time are three things, in my opinion:

Increase the length of the long run
Your long run needs to go up in length. I like to see runners hitting the 20 miles a number of times in their training. When you want to race your marathon and run at the top of your ability, getting familiar with 20-ish milers is a must.

Increase your overall mileage
Additionally, I'd like to see you increase your overall mileage. It would be great if you could fit in another easy run. When increasing your mileage, make sure to do it safely.

Do a mid-week long run
The mid-week long run is one of the secrets to marathon success. Everybody knows about the long run. Not everybody knows about the mid-week long run. Try to incorporate a mid-week run of at least 90 minutes. Build up to this gradually if you are not there yet. You don't want to rush it.

Tempo and Goal Pace Runs

You asked about running at sub-9 mile pace. Now tempo and goal pace runs will help get you there by getting used to that pace in training.

Tempo runs are crucial for improving your lactic acid threshold, which makes you faster and more efficient. A tempo run is typically a run at a "comfortably hard" pace—effort. Tempo pace is the pace you could sustain for an hour but not much longer. For you that appears to be a little slower than 10k pace.

You can do tempo intervals, e.g. 4 x 5 minutes tempo with 2 minutes jogging in between. Check out my tempo running page for more information.

Additionally, it would be beneficial to do some of your training at half marathon or marathon pace. Get used to that pace and know what it feels like to dial it in. A good approach is to incorporate marathon pace blocks into your long runs. This helps your body get used to running that pace on somewhat tired legs. You can start by alternating 1 mile at easy pace with 1 mile at goal pace. You can build up to longer marathon pace blocks over time.

These types of long runs are really, really hard. Both mentally and physically as they simulate the later stages of the marathon.

This gives you the broad outlines of what I would focus on in the next three months to improve your half marathon and marathon PBs. By focusing on long runs, mid-week long runs, increasing your overall mileage wisely, and incorporating tempo runs and marathon pace blocks, you'll build the stamina and speed needed for better performances.

Remember though, it's essential to listen to your body and adjust the plan if needed. Recovery and consistency are just as important as the workouts themselves. When you increase mileage and intensity, you increase the risk of injury. But with dedication and smart training, you'll be well on your way to crushing those personal bests.

I hope this helps, and best of luck with your training!
Kind regards,
Dominique