The Marathon Long Run: How to Build From 10km to 32km Safely

Why the long run is the cornerstone of marathon training

Every marathon plan is built around one weekly session: the long run. It does more than any other workout to get you ready for race day. Long, steady running teaches your body to burn fat for fuel, builds capillaries that deliver oxygen to your muscles, and toughens your tendons, ligaments and joints for hours of repeated impact.

It also builds something you cannot measure on a watch: confidence. Standing on the start line knowing you have already run 32km in training makes the distance feel possible. The long run is where you rehearse pacing, fuelling and the simple act of staying patient when your legs get tired.

How often should you do a long run?

For most runners the answer is once a week, usually at the weekend when you have more time. One quality long run per week gives your body the stimulus it needs while leaving enough recovery days around it. Running long twice a week is rarely needed for a first marathon and often leads to fatigue or injury.

With Edge, the long run already sits inside your coach-built weekly plan, so you do not have to guess where it belongs. If your default day does not work, use Flexi Swap to manually move the session to the weekend day that suits your life.

Progressing distance sensibly

The golden rule is patience. A safe build adds roughly 1 to 2km to your long run each week, then drops back every 3 to 4 weeks with a shorter cut-back run. These easier weeks let your body absorb the training and reduce the risk of overuse injury.

Think of it as two steps forward, one step back. You are not trying to set a personal best every weekend. You are slowly stretching the distance your body can handle, then giving it a chance to adapt before you push again.

Why most plans peak at 32km, not 42km

It surprises many first-time marathoners that they never run the full distance in training. Most plans peak around 32km, or 20 miles. The reason is simple: the last 10km of a marathon is fuelled by race-day adrenaline, your taper, fresh legs and proper carb loading. Running 42km in training would leave you so fatigued that the recovery cost outweighs any benefit, and the injury risk climbs sharply.

Trust the process. If you can comfortably cover 32km in training, the combination of taper, crowd support and good fuelling will carry you through the remaining distance on the day.

Long-run pace: keep it easy

The most common mistake in marathon training is running the long run too fast. Your long run should be easy and conversational. A good rule of thumb is to run it around 60 to 90 seconds per kilometre slower than your goal marathon pace. You should be able to hold a chat without gasping.

Why so slow? Easy running builds the aerobic engine and durability you need without the deep fatigue of harder efforts. Going too fast turns a steady endurance session into a hard workout, which slows recovery and raises your injury risk. Save the speed for your dedicated faster sessions during the week.

Edge can carry your easy long-run pace straight to your wrist. Voice prompts and structured workouts push to your Garmin, Coros or Apple Watch, so it is easier to hold back and stay in the right zone instead of drifting too quick.

Fuelling and hydration on long runs

Once your long runs pass roughly 90 minutes, you need to take on fuel. The long run is the place to practise this, never the race. A rough starting point is 30 to 60 grams of carbohydrate per hour, taken in small amounts every 20 to 30 minutes rather than all at once. Gels, chews and sports drinks are all options, and your gut needs training to handle them just like your legs do.

For hydration, sip little and often rather than gulping. In warmer conditions you will need more, and adding electrolytes helps replace what you lose through sweat. The key principle is to test everything in training so nothing on race day is a surprise. Find the brand, flavour and timing that sit well with your stomach long before the start line.

Time on feet vs distance for slower runners

Distance targets can be unfair on slower runners. A 32km long run might take one runner two and a half hours and another more than four. Spending over four hours on your feet in a single session carries a heavy recovery and injury cost. If that is you, it often makes sense to cap your longest runs by time, for example around 3 to 3.5 hours, rather than chasing a specific distance.

Time on feet still delivers the endurance benefits you are after. The goal is durability and confidence, and you can build both without grinding out an extreme number of hours in one go.

A sample long-run progression

Here is what a sensible build might look like over a marathon block. Notice the steady rise, the cut-back weeks, and the gentle taper before race day. Your own plan should flex around your starting fitness.

Edge progress tracking shows this build over time, so you can see your longest runs climbing and trust that the work is adding up. It is a quiet motivator when the early starts feel hard.

Common mistakes to avoid

Three errors trip up most marathoners. The first is running too fast, turning an easy session into a hard one. The second is going too long too soon, stacking big jumps in distance that the body cannot absorb. The third is skipping fuel, then wondering why the wheels come off after two hours. Avoid these three and you are already ahead of most first-timers.

Frequently asked questions

How long is too long for a marathon long run?
For most runners, much beyond 32km offers little extra benefit while adding a lot of fatigue and injury risk. If you are a slower runner, capping the session by time, around 3 to 3.5 hours, is often wiser than chasing a set distance.

What pace should I run my long run at?
Easy and conversational, roughly 60 to 90 seconds per kilometre slower than your goal marathon pace. If you cannot hold a chat, you are going too fast.

Are walk breaks allowed on a long run?
Absolutely. Planned walk breaks are a smart strategy for many runners, especially when building up or covering longer distances. They can lower fatigue and help you finish stronger.

How many 32km runs should I do?
One or two peak long runs of around 32km is plenty for most plans. There is no need to repeat them again and again, as each one carries a meaningful recovery cost.

When should I start practising fuelling?
Once your long runs pass roughly 90 minutes. Practise your gels, chews and drinks in training so race day holds no surprises, and never try anything new on the day itself.