The long run is the one session almost every training plan agrees on. It is also the one runners most often get wrong: too fast, too long too soon, or with no food until they hit a wall. This guide covers what the long run is for, how long and how fast it should be for your race, how to build it, and how to fuel and recover from it.
What the long run does
Time on your feet is the point. Long, steady running is widely thought to improve your aerobic fitness and help your body get better at using fuel over long efforts. Coaches broadly agree on the effect even where the exact physiology is still argued over.
The practical benefits are easier to pin down:
- Your legs, joints and feet get used to running for a long time.
- You learn what it feels like to keep going when you are tired, without racing.
- You get to practise everything for race day: kit, shoes, food, drink and pacing.
For a 5K the long run is useful support. For a half or a marathon it is the backbone of the plan.
How long should your long run be
These are the longest long runs in Run-R plans. Where you land in the range depends on your current level and how many weeks you have.
| Race | Longest long run |
|---|---|
| 5K | 7 to 14 km |
| 10K | 10 to 18 km |
| Half marathon | 16 to 22 km |
| Marathon | 32 to 35 km, or 3 hours (26 km or 3.5 hours for slower runners) |
You do not need to run the full race distance in training for a half or a marathon. Race day adrenaline, a taper and a sensible pace cover the gap. Running 42 km in training costs a lot of recovery for little extra benefit. Many coaches also cap the long run by time rather than distance, so slower runners are not out for far longer than faster ones. Run-R does both: a marathon long run stops at 3 hours, and other long runs at 150 minutes (Jack Daniels' limit), whichever comes first. If 3 hours at your easy pace is under 26 km, a marathon long run goes on to 26 km or 3.5 hours, whichever comes first, so slower runners still get a real step towards race day. On three or four days a week the long run can be up to half the week, as in Hal Higdon's novice plans.
How fast to run it
Most long runs should be at easy pace, around the middle of your easy range. For a 25:00 5K runner, Run-R's long run pace is 6:37 per km; for a 20:00 runner, 5:23; for a 30:00 runner, 7:50. It should feel conversational for most of the run and only get tiring near the end because of the time, not the speed.
Running it faster than that does not make it better. It just makes it harder to recover from, and it eats into the week's quality sessions. The easy running guide explains why slow running works.
Goal pace finishes
There is one exception. In the peak weeks of Run-R's half marathon and marathon plans, every other long run finishes at goal pace. You run most of it easy, then pick up to race pace for the final stretch. It teaches you to hold race pace on tired legs and gives you a chance to rehearse your fuelling at race speed. For a 25:00 5K runner, marathon pace is 5:38 per km.
Keep the easy part truly easy so you have something left for the finish. If you cannot hold goal pace at the end, the goal may need a rethink, and the race time predictor is a good reality check.
How to build it
The long run should grow steadily, not in leaps.
- Small steps. Add a little at a time, often a kilometre or two.
- Cutback weeks. Every fourth week in a Run-R plan (every third for new runners) is an easier week, and the long run drops back too. Then it builds again from a little above where it was.
- Avoid big jumps. A 2025 study of over 5,000 runners (Frandsen and colleagues) found injury risk rose when a single run was more than 10% longer than the longest run of the previous 30 days. Run-R holds every run to that. A Danish study of novice runners (Nielsen and colleagues, 2014) also linked weekly increases of more than about 30% over two weeks to more injuries.
- Keep it on the same day. Run-R puts the long run on Sunday and keeps the day before easy, so you start fresh.
How much of your week it should be
The long run is a big chunk of your weekly volume, but it should not be most of it. In Run-R's half marathon and marathon plans it is often up to about a third of the week. If your long run is much more than that, you probably need more running on the other days before the long run grows further.
Runners on three days a week feel this most, because one long run is a big share of only three. That is fine early on, but it is a reason to build the other runs too.
Fuelling on long runs
For runs under about 75 to 90 minutes, most people do not need to eat on the way round. Have a normal meal or snack a couple of hours before and some water to hand if it is warm.
Beyond that, carbohydrate helps. The long-standing guidance from the American College of Sports Medicine is 30 to 60 g of carbohydrate per hour. For events longer than about 2.5 hours, up to about 90 g per hour can work, using products that mix glucose and fructose, but only if you have trained your gut to handle it.
Most gels contain about 20 to 30 g of carbohydrate, so check the label. As an example, a 25 g gel every 30 minutes gives 50 g an hour, inside the usual range. Chews, drinks and real food such as bananas all work too; the right choice is the one your stomach agrees with.
Drinking
Drink to thirst. Over-drinking can cause hyponatraemia, a low level of sodium in the blood, which is dangerous. You do not need to force down water on a schedule. Some gels are designed to be taken with water, so read the packet.
Practise race-day fuel
The long run is where you test your race plan. Use the same gels or drinks you will use on race day, at the same times, in the same kit. Find out what your race provides on the course and practise with that, or plan to carry your own.
Start with a smaller amount and build up over several weeks. Stomach trouble on a long run is useful information. On race day it is a problem. The race pacing guide covers race-day food in more detail.
Recovery after the long run
- Eat. A proper meal with carbohydrate and protein within a few hours helps you refuel.
- Rest or go easy the next day. Run-R never puts a hard session the day after a long run.
- Sleep. Adults are generally advised 7 to 9 hours, and the night after a long run is a good one to protect.
Tired legs are normal. Pain that changes how you walk or run, or that gets worse, is not: see a GP or physio. Stop at once for sharp pain, chest pain or dizziness.
Find your long run
If you want your long runs mapped out week by week, the Run-R plan builder sets the distance, pace and cutback weeks for your race. For race-specific detail, see the half marathon plan or the marathon plan.