The Ultimate Guide: Building Your Aerobic Base for Running

This post is going to teach you everything you need to know to build a solid aerobic base for running.

Even a 5km race is thought to be 90% aerobic. So whether you’re a seasoned runner or a beginner, building your aerobic base is crucial if you want to run faster, for longer, or both.

Building a solid aerobic base takes discipline and consistency — you need to run slowly, run a lot, and do so over a period of 8–12 weeks. It’s tough, and it can be boring, but it’s worth it.

I was able to shave more than a minute off my 5km time in 8 weeks by following a dedicated aerobic base building plan.

In this post, I’m going to cover:

• What it is
• Why it’s so important
• How to know if you need to improve your aerobic base
• The key components of aerobic base training
• How to build an aerobic base training plan for yourself
• How to monitor progress and adjust your plan
• Common mistakes

Let’s get stuck in.

Aerobic Base Training Explained

Aerobic base training is any form of training designed to increase the capacity of your aerobic energy system — the system that uses fat and oxygen for fuel and allows you to run for long periods of time.

Aerobic base training runs are simply runs performed in Zone 2, at or below your aerobic threshold.

Your aerobic threshold is the limit at which your aerobic system works maximally. Above that threshold, your glycolytic/lactate and anaerobic system will gradually contribute more.

Training to increase your aerobic capacity or threshold will allow you to run long distances at faster paces — exactly what we’re all trying to achieve!

Why is it so important to build an aerobic base for running?

If you want to complete any running events beyond the 1500m, your aerobic capacity will be the primary factor dictating how fast you can run.

My favourite way of thinking about your aerobic base is by likening your fitness to a pyramid, where the height of the pyramid is determined by your top-end fitness (VO2 max), and the width of the pyramid is determined by your aerobic base. The bigger the pyramid, the higher your level of fitness.

If you were trying to build the tallest pyramid in the shortest time, you wouldn’t spend much time building the foundations. Instead, you’d focus on stacking bricks on top of each other to make it as tall as possible by performing high-intensity workouts (tempo, threshold, interval and VO2 max sessions).

If you kept this up for long enough, eventually, it’d reach a point where it’d either topple over (you suffer an injury), or you’d reach a point where you can’t go any higher as adding more bricks would make the pyramid unstable (you plateau or pick up niggles).

Side note: This is a viable option for building maximum fitness in a limited time, and it’s how many race training programmes work. It can work well for cycling, but it’s a risky approach for high-impact sports like running.

But if you wanted to make the pyramid as tall as possible and had longer to do so, you’d invest a lot of time at the beginning in building the foundations — an aerobic base.

Once you had a solid base, you could then build vertically by adding in more tempo, threshold and interval workouts. If, at any point, trying to make the pyramid any taller would make it unstable, you’d go back and put more time into building the base before building up again.

In short, the size of your aerobic base limits how fit you can get.

How to know if an aerobic base training phase is right for you?

If you fit into one of these buckets, it’s worth considering performing an aerobic base phase:

• You’re a beginner or intermediate runner who wants to be able to run further.
• You feel like your aerobic capacity is lacking.
• You want to increase your training volume.
• You’ve just come off a tough race prep and feel like your body needs a phase of lower-intensity training.
• You have a race booked in, and you’re race training plan doesn’t start for 2–4 months.

How to build an aerobic base

In principle, building an aerobic base is really simple. All you need to do is perform the majority of your training at an easy, zone 2 effort and gradually increase your weekly aerobic training volume over time.

The core components of aerobic base building training plans are:

• Lot’s of easy, zone 2 runs and workouts
• 1x long run each week
• 1–2x faster runs each week to maintain leg strength and speed
• Steady, 5–10% increases in weekly mileage
• A deload every 4th week
• Consistency over an 8–16 week period

Most good running training programs will have a similar structure to the above. The only real difference is that in an aerobic base training program, 80–90% of your weekly training volume will be at an easy intensity versus 60–80% in most race training plans.

How to design your own aerobic base-building training plan

If you think it’s the right time for you to do an aerobic base-building training phase, here are the steps you can take to build your own plan.

Step 1: Determine your zone 2 heart rate range

You’re going to be doing a lot of easy running, so it’s important to know your Zone 2 heart rate so you can make sure your effort is sufficiently easy.

The best way to determine your heart rate zones is to use the Karvonen Method. This formula takes into account your resting and maximum heart rate to calculate heart rate ranges for each training zone. You can use the free calculator here. This page also provides guidance on calculating your max and resting heart rates and some limitations with heart rate training that you need to be aware of.

I recommend setting up all your easy runs on your watch or wearable with a heart rate alert so that it pings whenever you slip out of Zone 2. After your first few runs, you’ll understand what pace you need to run at to stay in Zone 2.

Step 2: Determine your weekly mileage targets

The next step is to determine what level of mileage you want to start the plan with.

As mentioned, one key factor in aerobic base building is regular 5–10% weekly increases in volume. So it’s important to start conservatively, as your mileage will be quite high by the end of the plan.

I suggest being conservative in selecting your starting mileage at a level that you can comfortably handle. The first couple of weeks should feel easy.

Using me as an example, I’ve just started a 9-week base building plan after taking a few weeks off after running the Manchester marathon. The highest my weekly mileage has ever been is around 55km, so I’m starting the plan at 35km in week 1 and increasing mileage up to 65km in week 9.

If you want to follow my training in the lead up to a sub-3 attempt in April 2025, you can check out my training log here.

Step 3: Determine how many runs you want to perform each week

This is mainly dependent on your weekly mileage:

• If you run less than 25km in a week, it’s feasible to do so by running only 3x per week.
• If you’re running between 25–40km per week, I’d suggest running at least 4x per week.
• If you’re running between 45–70km per week, I’d suggest running at least 5x per week.
• And if you’re running more than 70km per week, you’d need to be running 6x plus per week.

Taking my plan as an example, I’m starting with 4 runs per week and then moving to 5 once weekly mileage exceeds 40km.

Step 4: Setting up your workouts

In this step, you need to work out how you’re splitting your target weekly mileage across however many runs you’re doing that week.

As a reminder, the core components of an aerobic base training plan are:

• Lot’s of easy, zone 2 workouts
• One long run each week
• One or two faster runs each week to maintain leg strength and speed

There are lots of ways to go about it, but here’s a simple method you can use:

• If you’re running 4 or more times per week, work out your long run distance by taking 25–35% of your weekly mileage.
• If you’re running 3x per week, your long run should be 40–50% of your weekly mileage
• Divide the remaining mileage evenly between the remainder of your runs.
• Allocate one of these as a threshold or interval run, the others should all be easy, Zone 2 runs.
• Optional: add one more faster effort into the week, you can either do this by adding strides or hill sprints after an easy run, or you can turn your long run into a progressive run (e.g. a 16km long run could look like 10km easy, 4km @ marathon pace, 2km @ half marathon pace).

After doing this, review your plan to make sure at least 80% of your weekly volume is at an easy Zone 2 level. If not, you may need to replace some of the faster running with more easy running.

Step 5: Allocating Deloads

Every fourth week, take a deload week where you decrease weekly mileage by 30–50%. You can so this by shortening each run or skipping 1–2 runs.

How much you deload will depend on how fatigued you are. If you picked up any niggles or injuries, you could take a week off completely.

It’s also a good idea to drop intensity levels in a deload week, so I’d suggest making your weekly threshold/interval workout much easier or skipping it entirely.

Step 6: (Optional) Add Cross-training

This one’s optional because it depends on how much free time you have each week.

Cross-training refers to any activity other than running that still provides aerobic benefits e.g. swimming, cycling or rowing.

Cross-training allows you to increase weekly training volume without dealing with more of the impact forces inherent in running, reducing your risk of overuse injury (relative to if you were to increase volume by adding more running).

If you’re someone who’s particularly prone to injury when increasing running volume, cross-training can be a great way to build an aerobic base — aerobic base training doesn’t all have to be running. Simply replace 1–2 runs per week with cross-training instead.

It can also provide a welcome break from running and allows you to target different muscle groups to improve overall muscular balance.

One caveat is that if you’re struggling for time and you have to choose between cross-training and strength training, I’d pick strength training every day of the week. Strength training is a key contributor to health, mobility and longevity.

Step 7: Monitor Progress

Before you begin the plan you want to determine a benchmark that you will use to judge your progress.

There are a lot of ways to do this, but two I use are:

• Pick a flattish route that you can run regularly. Use the route to run an easy, Zone 2 run. Record your finish time, average pace and average heart rate. Repeat this regularly throughout your training plan, after 4–6 weeks, you should see that you can run the route faster at the same or lower average heart rate. Don’t worry if you don’t see week-on-week improvements, be patient.
• Running a 5km max effort. Repeat every 4–6 weeks. You should see your 5km time improving.

If you see improvements in either of these benchmarks, you know your training is working.

As an example, here are two easy runs from my last aerobic base training block, performed 8 weeks apart, running an identical route:

If you don’t see results after 6 weeks, you need to consider the following and adjust what you’re doing appropriately:

• Is your weekly mileage too high or too low?
• Are you sleeping and eating enough?
• Are you truly performing your easy runs in Zone 2?
• Is your interval or threshold workout too hard?

I go into each of these more in the Common Mistakes section.

Step 8: Auto-Regulate

A training plan is just that — a plan.

You’re unlikely to get it spot on when you first write it — who know’s how you’ll feel 8-weeks from now and what else will come up in your life between now and then?

You shouldn’t expect to follow it exactly as you first wrote with 100% compliance. Some days you might feel crap, you might have a really busy week at work, or you might feel like it’s too easy and want to do more.

There should always be an element of auto-regulation when it comes to training. You start with a plan, and you adjust as you go.

This week was the first week of my base training plan. I was meant to run a total of 35km, but I only managed 26.5km because a hip injury I picked up training for my last marathon flared up again, limiting how far I can run in one go.

I could have pushed through, but that would risk causing a bigger issue in a week or two’s time. Instead, I lowered my expectations, cut each of my runs short as an when I felt my hip starting to flare up, and spent more time stretching and foam rolling it.

Aim for 90% compliance. You will still get great results.

Common Mistakes

1. Too much volume

As alluded to earlier, it’s best to be conservative with your starting weekly mileage. The worst thing you can do is develop an overuse injury three weeks into the program from doing too much running too soon.

If you’re also performing cross-training and strength training, your overall weekly training volume may be too high. If that’s the case, drop the cross-training first.

A bit of wisdom I picked up from Olympic marathoner Stephen Scullion is that your goal as a runner is to get through the training whilst picking up as little damage to the body as possible.

It’s a good quote to keep in mind as you set up and go through any training program.

2. Neglecting recovery

Some people think of aerobic base training as the “off-season”, where they can do whatever they like. But although most of the running is at an easy pace, the volume is still high, so the recovery demand is still there.

You don’t need to take it as seriously as when you’re in the middle of marathon prep, but you still need to make sure you’re sleeping and eating enough.

3. Running your easy runs too fast

The biggest and most common mistake you can make when base building is running your easy runs too fast and running in Zone 3 instead.

There’s nothing wrong with running in Zone 3 in and of itself, but there is if you’re actually meant to be running in Zone 2.

Your aerobic system is still working to a high degree when running in Zone 3, but it is more strenuous on the body, so the recovery demand and impact forces are higher.

The main risk is that if you keep making this mistake run after run and week after week, you’ll end fatigued, and it’s likely you’ll pick up an overuse injury or two.

Running in Zone 2 can be boring, and there’s always the temptation to run faster, but stick with it. Put on a podcast or audiobook to help pass the time.

If you’re struggling to run in Zone 2, I have a post for that → Why Can’t I Stay In Zone 2 When Running?

4. Running your interval or threshold workouts too hard

These workouts are the most taxing of the week. If you push them too hard, they can take a lot out of you and leave you sore for days, causing you to underperform in the next couple of runs.

You can tell if you’re running them at the right intensity in a few ways:

• You should still be able to hit your target pace even in your last interval or at the end of your threshold run.
• You should be able to keep going a little bit further if you really had to.
• The run should feel like an 8–8.5/10 effort. Hard but not maximal.

If you need to adjust your weekly hard run, you can do so by reducing your pace, increasing your rest periods, or shortening your distances.

Key Takeaways

To summarise, here are the steps you need to follow to build an aerobic base for running:

• Select a conservative weekly mileage to start your plan, then increase it by 5–10% each week.
• Include one longer run per week, making up 25–30% of your weekly training volume.
• Include one faster-paced run — either a tempo, threshold or interval run.
• Include one easy cross-training session per week if you have time.
• Perform 80–90% of your total weekly training at Zone 2, below your aerobic threshold.
• Deload every fourth week, reducing weekly mileage by 30–50% depending on how fatigued you feel.