How to train for a marathon

Before lacing up your running shoes and embarking on marathon training, it’s important to ask yourself: why do you run?

Whether you’re chasing a personal best or simply aiming to cross the finish line, understanding your motivation is key.

This applies not just for race day, but for every training run, especially those after a long day at work, or when motivation is low.

After your long run, threshold sessions are some of the most valuable workouts you can do. Run at a steady but challenging pace, around 80–85% of your maximum heart rate (MHR), where conversation is limited to just a few words.

These runs improve your lactate threshold, running efficiency and aerobic endurance, helping you maintain speed for longer.

The foundation of any training plan, long runs are essential for building endurance for races from 5K to marathons. Focus on time on your feet rather than distance at first, running at a comfortable, conversational pace (around 6/10 effort).

Over time, you’ll introduce marathon or race-pace efforts, gradually working up to 75% MHR. These runs improve muscular endurance and train your body to use fat as a fuel source.

Vital if you’re going to stay the course during a marathon.

Hill training builds muscle strength and resilience while reducing impact stress compared to fast-paced running. Find a steady 5–10% incline and run up for 45–90 seconds at threshold effort.

Without pausing, turn at the top and descend at the same effort, then repeat continuously until the session is complete.

Like a threshold run, this is a workout that demands focus, expect to be working at 80–85% MHR, with just enough breath for short phrases with a running mate.

Fun, but horrific.

Yes, this counts as training. Recovery is as crucial as running itself, allowing your body to adapt and grow stronger.

Listen to the warning signs: if you're exhausted before you even start, constantly making excuses, or picking up minor injuries, it's time to take a step back.

Prioritising rest prevents burnout and ensures both physical and mental resilience.

Don’t be stupid. Look after yourself and try to be objective. 

We’ve broken down the training into four phases, taking place over 16 weeks.

To make things easier to visualise, we’ve also added the months, using a spring marathon as an example for the end goal.

This phase is all about gradually increasing your running volume and frequency without overloading your body.

Focus on consistency, slowly incorporating longer runs to build muscular endurance. 

The key is to create a solid foundation without risking injury.

By now, your training plan should have structure. Volume rise, as will the intensity of harder sessions.

This is also the time to test your race-day nutrition strategy—experiment with different gels and hydration methods to see what works for you.

“It’s just as important to train your stomach as it is to train your legs”, says George. “You need to work out how to fuel yourself before and during your long runs.”

“Everyone is different. You just need to work out what is best for your body and metabolism”, adds Josh.

This will be your toughest month.

Expect to feel fatigued, but just remember that you're nearly there. The majority of your fitness will be built during this phase.

Your long runs will be at their peak, and your body will be pushed to its limits to prepare for race day.

Fuel up. It’s time now to prioritise your training, which means sacrifices. Your social life may suffer a little. This is what we mean by sacrifice.

Tapering begins. This is when your training volume decreases, and you focus on mental preparation.

Visualisation exercises, such as imagining yourself crossing the finish line, can be powerful tools. 

By now, you should have a clear idea of your target pace and fuelling strategy. You’ve trained your stomach as well as your legs.

Tapering means reducing your training volume 2-3 weeks before the race to allow your body to recover.

The goal is to arrive at the start line with fresh legs and optimal energy levels.

You’ve probably heard of it.

Many studies suggest that carb loading improves performance. How do you do it? Well, a few days before the race, increase your carbohydrate intake to maximise your body's glycogen stores. Easy. 

This will help maintain your energy levels throughout the marathon. However, stick to foods that work for you. Race week isn’t the time for dietary experiments.

If you can get pizza down you, go for pizza. If it’s pasta, do that. It’s just about getting those carbohydrates in. 

Prioritise good sleep in the days leading up to the race. You may not sleep well the night before the race, but don’t worry, this is normal. Even professional athletes struggle with this.

As long as you get good sleep in the days prior, you’ll be fine.
A short shakeout run the day before can help keep your legs feeling fresh without overexerting yourself.

“We’re talking at extremely low intensity here. Maybe 1-2k. Keep it super slow”, advises Josh.

This is just about getting blood flow to your legs. A little shake-out.”

Visit the expo early and get your race number sorted.

- Lay out your kit the night before.
- Stick to familiar foods and avoid new gear on race day.
- Know your route to the start line to prevent last-minute stress.
- Plan a breakfast that fuels you effectively. 

“Don’t do anything new”, is the message emphasised here by both George and Josh.

Excitement will be high at the start. Control your pace and avoid going out too fast. The first 10km should feel comfortable. Running with a pack can help maintain an even effort.

By now, you should still feel in control. Resist the urge to push too soon—there’s a long way to go.

Around the 32km mark, your body will start shutting down, entering a state of hypoglycemia, commonly known as ‘hitting the wall’.

Your carbohydrate stores deplete, fatigue sets in, and suddenly every step becomes a battle. 

This is what makes the marathon special.
Before the 1880s, scientists believed humans physically couldn't run beyond 32km due to these constraints. But time and time again, runners have proven otherwise.

While proper fuelling and strategy can help, your mindset is the true game-changer. Developing mental fortitude before race day will give you the strength to push past those barriers and reach the finish line.

This is where you’ll really need to dig deep and get it done. Why you’re running is vital here to get you through it.

Your body will be exhausted, but adrenaline and crowd support can help push you through. Keep your eyes on the finish line and continue to draw motivation from your "why."

Remember to smile at the finish line. There will be photos.

Lay out your running clothes the night before.

Eat a familiar breakfast 2-3 hours before the start. Don’t try anything new - bring your own bagels if you have to.

Arrive early to avoid unnecessary stress. Aim for 1-1.5 hours prior.

Use the bathroom before heading to your corral.

Stick to your pacing plan.

Break the race into smaller segments.

Research the course and know where the hills are.

Smile and soak in the moment—crossing the finish line is a huge achievement.

Take time to reconnect with family and friends.

Celebrate not just the race, but the journey and discipline that got you there.

Most importantly, enjoy the process. Running a marathon is about more than just race day—it's about the transformation along the way.

“After the race, savour and enjoy the moment with your family”, says George.
“You might have had to sacrifice time with your loved ones over the past couple of months - now is the time to make up for it. Have a beer. Relax. Even if you didn’t get the tie you want, make sure to realise the magnitude of your achievement” 

At its core, running is the simplest of sports. While strategy, training plans and preparation all play their part, don’t overcomplicate things—when race day arrives, just focus on putting one foot in front of the other.

Think of the marathon as just another Sunday run, only with a bigger crowd and a lot more energy.

The atmosphere, the support, and the collective determination of thousands of runners will help carry you forward. Be present, soak in every moment, and enjoy the experience.

Your first marathon will be unforgettable—it might even change the course of your life. The discipline, resilience, and self-belief you build through training will stay with you long after you cross the finish line.

And remember, you’re capable of far more than you think. Trust in your preparation, believe in yourself, and go make it happen.

Ranked 9th in the UK from 2024-2025 for the 20-mile distance, 12th in the UK in 2022 for the 50 mile (82 km distance).

Member of Belgrave Harriers (the UK's most successful running club)

2:41 marathon runner (aiming for even faster).

Decathlon’s running department chief for 4 years

5k 17:53, 10k 37:55, Half-marathon 1:28:05

Join us at Decathlon Surrey Quays for the Kiprun Run Club. It doesn’t matter how long you have been running, we’d love to have you join us.

We run a beautiful 5k route, starting at our store in Canada Water, down towards Tower Bridge and back, taking in the scenery along the Thames.

We have a variety of pace groups led by our fantastic pacing team, so you can run at whatever pace you feel comfortable at.