The long slow run is not just for marathon or half marathon runners. Middle distance runners training for anything from a 5k to a 10k should also be incorporating the long slow run into their weekly training. Obviously, there is going to be a huge difference in the distance covered by a 5k runner compared with someone training for a marathon, but the premise is exactly the same throughout: run for longer at a controlled, comfortable effort to develop your endurance.
For some runners, seeing the long slow run on the training plan fills them with dread, while for others it is the most enjoyable session of the week. Then there are the runners who struggle with the “slow” far more than the “long”. They could happily head out and run 15km, but asking them to slow the pace down can be surprisingly difficult.
In my experience, this can be particularly noticeable when you get a group of runners together, and perhaps even more so when you have a group of male runners and a little bit of ego enters the equation. Nobody wants to be seen running slowly. Suddenly, an easy long run becomes an unofficial race, with everyone trying not to be the one who gets dropped.
While there is nothing wrong with a little healthy competition, the long slow run is not the place to prove how fast you are. The pace has a purpose, and running faster is not necessarily going to make the session more beneficial.
The long slow run is one of the most important sessions for developing endurance because it creates a range of physiological adaptations within the cardiovascular system, muscles, energy systems and connective tissues. The aim is to provide your body with enough training stimulus to encourage adaptation without creating so much fatigue and physical stress that you are unable to train for the rest of the week!
The Long Slow Run Explained
The long slow run is a longer period of running completed at low intensity, ideally at a pace where you can maintain a conversation without becoming breathless.
The exact pace will be different for every runner. Someone who has been running for years might complete their long run at a pace that would be a challenging effort for a newer runner, while a beginner may need to include walking breaks to keep the overall effort comfortable.
This is why pace alone is not particularly useful when deciding whether you are running your long run correctly. The effort and how your body responds are much more important.
A useful guide is the conversation test. You should be able to speak in reasonably complete sentences while running. If you can only manage a few words before needing another breath, your pace has probably crept too high. And if you think you are going too fast, then you probably are.
The long slow run should feel controlled rather than challenging, and you should finish knowing that you have worked but that you haven’t completely emptied the tank.
The Overall Purpose of The Long Slow Run
Understanding the real benefit of incorporating this session into your training will help you perform it more effectively, in other words, not too fast or too far.
There is a lot happening inside your body during a long slow run, even though the pace feels relatively easy.
Improved Cardiovascular Efficiency
One of the most important adaptations occurs within your cardiovascular system. When you run, your muscles require a continuous supply of oxygen and nutrients, while carbon dioxide and other metabolic by-products need to be transported away. Your heart, blood vessels, lungs and muscles all work together to meet this demand.
Repeated aerobic training can improve the efficiency of this system. Your heart can become more effective at pumping blood with each beat, while your cardiovascular system becomes better at delivering oxygen to the working muscles. Regular endurance training also supports improvements in the network of small blood vessels, known as capillaries, that supply your muscles.
This means your body becomes better at delivering oxygen where it is needed, allowing your muscles to produce energy aerobically for longer.
Your muscles become better at using oxygen
Another important adaptation takes place inside the muscle cells themselves.
Within your muscles are structures called mitochondria, which produce much of the energy your body needs during aerobic exercise. Endurance training can increase mitochondrial density and improve mitochondrial function, making your muscles better equipped to use oxygen to produce energy.
This is particularly important for distance runners because aerobic energy production allows you to keep running for extended periods without the rapid accumulation of fatigue associated with harder efforts.
Your muscles also become better at extracting and using the oxygen delivered to them. Over time, this can make a previously difficult pace feel more comfortable and sustainable.
These changes do not happen because of one particularly long run. They are the result of consistently completing endurance training and allowing your body enough time to recover and adapt.
Long slow runs and fat as fuel
Your body uses a combination of carbohydrate and fat for energy when you run, with the balance changing according to intensity, duration, fitness and other factors.
At lower intensities, your body can rely more heavily on fat oxidation because the energy demand is relatively manageable. As intensity increases, carbohydrate becomes increasingly important because it can be converted into usable energy more quickly, however these stores get used up quickly.
Consistent endurance training can improve your muscles’ ability to use fat as a fuel source at lower intensities. This can help preserve some of your limited carbohydrate stores for later in a long race or during harder efforts.
Your long run builds resistance to fatigue
Long slow running also helps your body cope with the physical demands of running for a prolonged period.
Your muscles, tendons, ligaments and bones are repeatedly exposed to the forces involved in running, and gradually increasing your training allows these tissues to adapt to the workload. Your muscles also become better at maintaining their work as fatigue develops.
This is one reason increasing your long run too quickly can cause problems. Your cardiovascular fitness can sometimes improve faster than your muscles and connective tissues can adapt, meaning you may feel capable of running further but your muscles are not quite ready for it.
The long slow run is therefore about developing both your ability to produce energy and your ability to keep physically moving when fatigue begins to build.
How Slow Should You Go?
There is no single pace that works for every runner, but a useful starting point for the Long Slow Run is around 1 to 2 minutes per mile slower than your goal race pace, which works out at approximately 35 to 75 seconds per kilometre slower. Some coaching guidance uses a percentage rather than a fixed pace difference, particularly for marathon training, because the difference between race pace and long-run pace varies according to the runner and their goal distance.
The most important test, however, is how the pace feels. Your long slow run should generally feel comfortable and conversational, around 3 or 4 out of 10 for effort. You should be able to speak in full sentences without gasping for breath.
For a 5K runner, that may mean considerably more than two minutes per mile slower than 5K race pace. For a marathon runner, the difference may be smaller. This is why using a fixed number on your watch can sometimes be less useful than learning what an easy, controlled effort actually feels like.
The pace is a guide. The effort is the priority.
The Issue With Going Too Fast.
This is one of the most common mistakes runners make.
You head out intending to run slowly, but the first few kilometres feel easy, so you gradually increase the pace. You are still not sprinting, but your supposedly easy long run has become a moderate or even hard session.
The problem is that you have changed the training stimulus. Instead of primarily developing aerobic endurance while keeping fatigue controlled, you have created considerably more stress, which can leave you tired for your next quality session and make recovery more difficult.
A well-designed training plan contains different sessions for different purposes. Intervals, tempo runs, hills and race-pace sessions provide opportunities to work at higher intensities, while easy and long runs allow you to develop endurance without constantly pushing your body to its limits.
The Problem With Going Too Slow
There is also a balance to be found at the other end of the scale.
If you deliberately slow your pace so much that you are barely running and your stride becomes more of an uncomfortable shuffle, you may find that walking breaks would be more effective.
This is particularly relevant for beginners and runners returning to training. There is absolutely no shame in using a run/walk strategy. Alternating periods of running with planned walking can allow you to accumulate more time on your feet while keeping the overall effort manageable.
For example, you could run for ten minutes and walk for one minute, repeating the pattern throughout the session.
If you are having to shuffle along at an extremely slow pace because you are determined not to walk, you may be better off running comfortably for a period and then taking a short walking break before returning to your running pace.
The goal is to build endurance, not to prove that you can avoid walking.
Longer is Not Always Better
One of the most important things to understand about long slow runs is that there is a point of diminishing returns. It is tempting to think that if running 15 kilometres is beneficial, then 20 must be better, and 25 must be better again. It does not quite work that way.
The purpose of the long run is to provide enough training stimulus to encourage adaptation without creating so much fatigue and physical stress that the cost of the session outweighs the benefit.
During a long run, you are challenging your aerobic system, using your glycogen stores, encouraging greater reliance on fat oxidation, recruiting your muscles over a prolonged period and exposing your bones, tendons and connective tissues to repeated loading.
However, these benefits do not continue increasing in a straight line for as long as you keep running. As duration increases, muscle damage, glycogen depletion and overall fatigue can also increase, potentially leaving you needing considerably longer to recover.
If a two-hour long run provides the endurance stimulus you need, running for four hours does not automatically give you twice the benefit. Instead, you are creating a much greater recovery requirement, which could affect the rest of your training.
This is particularly important for marathon runners. Completing 42.2km in training might seem like the ultimate preparation for a marathon, but there is a considerable difference between being capable of completing the distance and being able to recover from it sufficiently to continue training well.
That said, there are runners who prefer to cover the full marathon distance in training because they find it gives them confidence that they can physically complete the distance on race day. There is nothing wrong with this approach, but it is important to consider what happens afterwards. How do you feel in the days following your longest runs? How long does it take you to feel fully recovered and ready to train again? Some runners recover quickly from long runs, while others need considerably more time, and this should be taken into account when deciding how long your longest training run should be.
The goal is not to prove that you can run your goal distance before race day. It is to arrive at the start line having completed enough training to prepare your body, while still being able to recover and continue training effectively.
Increase Your Long Run Gradually
The general rule is do not increase your long run by more than 10% each time. The temptation when you feel good is to add distance quickly, but your body needs time to adapt to increased training loads. A half marathon runner might progress through 12km, 14km, 16km, reduce the distance for a recovery week and then build towards 18km and eventually 20km.
Marathon training follows the same principle, although the distances become much greater.
Your long run does not need to increase every week. Cut back weeks allow your body to absorb the training stimulus and are particularly important when your overall training load is increasing.
The Long Run is Your Endurance Laboratory
Your long slow run is where you learn what your body feels like after 60 minutes, 90 minutes, two hours or longer. It is where you can practise your fuelling, hydration, clothing, shoes, pacing and mental approach, while developing the physiological adaptations that allow you to keep running for longer.
You are also learning patience, an essential part of training.
The long slow run is not supposed to be impressive on your watch. It is supposed to prepare you for the point in your race when your body is tired but you still have more to cover.
Run it too fast and you risk turning an endurance session into another hard workout. Run it so slowly that you are barely running and planned walk breaks may be a better option. Run it considerably further than you need to and you can reach the point where the additional training benefit is outweighed by the fatigue and recovery required.
Find the pace where you can settle into a controlled rhythm, maintain conversational breathing and accumulate the appropriate amount of time on your feet for your goal.
The goal is not to run as far as possible. The goal is to run far enough to become a stronger, more durable runner, then recover well enough to do it all again.
That is where the real value of the long slow run lies. Train with structure, respect the easy pace, increase your distance gradually and give your body the recovery it needs. The adaptations may not be noticeable when you finish today’s long run, but over weeks and months, they build you into a better running machine that can sustain your goal pace for the duration of the race and allow you to cross that finish line feeling good.
If you would like some help building a training plan that takes into account your starting point, goal distance, target time and the time you have available to train, join us at ARC.
Regardless of how many days you can commit to training, we make sure your plan includes the right training stimulus to help you improve, while allowing time for recovery. You can also chat with our coaches to fine-tune your training and make adjustments along the way, helping you stay on track towards your goals.
Train with structure. Train with purpose. Believe and Achieve.
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