Sub 4:20 Marathon Goal – How Do I Get There?

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

I run 25-30 miles a week including 13m - 15m 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.

– Mark, UK (Brighton)

Answer by Dom:

Hi there,
Thanks for your question about improving your personal records on both the half and the full marathon. Here's how I'd approach it:

• What your race times are telling you
• Why sub-4:20 is tough despite good speed
• A weekly structure for your next three months
• Adding tempo running to the mix

What Your Race Times Are Telling You

First thing I did was plug in your results in the Race Conversion Calculator.

It's a useful tool to work out if your racing times are well aligned.

So, what I did was plug in your 5k time, then compare the expected 10k and half marathon times with your real times.

Based on your 5k time your expected 10k time is more than 30 seconds lower than your 53.03 PB and your expected half marathon time is about 2.5 minutes lower than your 1.58.04 PB.

Based on your 10k time, your expected half marathon time is a minute faster (1.57).

Additionally, your 4.20 sub-marathon goal as suggested by the title of your post appears to be within your abilities given your 5k, 10k and half marathon performances.

Why Sub-4:20 Is Tough Despite Good Speed

Your racing times are close, but not fully aligned. Why is this? And why will it be tough for you to hit sub-4.20, despite your performance in other races?

The answer? Your base, your basic stamina, is not yet developed fully enough. You have got the basic speed, but can't maintain it for long enough. You are getting there, it's not at all bad. But your aerobic base needs to become stronger. That's the absolute key to marathon success.

And the only way to solve it is by doing a lot of long runs and easy runs.

As I indicate in my marathon training tips the main component of a successful marathon is the long run, with the mid-week mid-long run being a close second.

A Weekly Structure for Your Next Three Months

You're currently at 25-30 miles a week. With a half marathon and a marathon both coming up in the next three months, that mileage needs to grow – sensibly, not in one leap.

Here's a rough weekly template to work towards over the coming weeks:

• Weekend long run: build this progressively so you hit 20 miles a few times before the marathon. If a session feels too hard to complete running throughout, turn it into a run/walk in which you run at least 70% of the time – you still get most of the endurance benefit and recovery is easier.
• Mid-week medium-long run: at least 90 minutes, once a week. Build up to this gradually rather than jumping in from next week.
• One tempo run a week: 20-30 minutes at a threshold effort, nested inside an easy run.
• Two to three easy runs: genuinely easy, conversational pace – these are what build your aerobic base.
• Total weekly mileage: aim to progress from your current 25-30 miles towards 35-40 miles a week by the time you're deep into marathon-specific training, using your mountain biking as active recovery on non-running days.

Use your half marathon, roughly midway through this block, as a fitness check rather than an all-out effort – it'll tell you whether your base is coming along and give you a fresh Race Conversion Calculator comparison ahead of the marathon.

The weekly longer long run and the mid-week long run together will do wonders for your stamina. They will help improve your times across all distances, but the differences will be most noticeable in your half marathon and marathon performances.

Adding Tempo Running to the Mix

Many runners settle into just one training speed. You can improve your performance by adding tempo running on top of your easy, steady-state base running.

Tempo runs help you improve your lactic acid threshold, which in turn helps make you a faster runner – and it's exactly this threshold work that will let those 8.30 miles in the middle of your half marathon hold on instead of slipping back to 9s.

Keep the base building patient and consistent, layer in that one tempo session a week, and the sub-9-minute pace you're chasing should start to feel a lot more comfortable, not just for a few miles, but for the whole distance.

I hope this helps.

Kind regards,
Dom

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