Long Runs to Build Endurance

This is the most important weekly run for amost all endurance runners. (By the way, do not start off or go too quickly or you will lose the value of the run. More about that at the end)

All training is based around practice and recovery. To improve endurance you should improve your ability to run by repeatedly pushing your boundaries, in a sensible way. Then after a period of fatigue you come back stronger. Simply repeating the same activity does not push your boundaries, in the same way as racing every week does not.

Gradually increasing the distance of your longest runs is an effective method for most runners to both improve endurance and provide a base for harder training. Without being too detailed or technical, among other benefits long runs stimulate your body to store more glycogen, which is the key fuel your muscles use when running and also to make your use of the energy from your fat stores more efficient.

The overall mileage you cover over a period also matters.

How far? How fast? How often?

If you are a relatively inexperienced 5k runner, over time you need to build to regular 10km or 12km on your weekly long runs. Experienced half marathoners need long runs of over 25km.  It’s different for every runner and is affected by many factors. Mileage limits do increase over time and you should be thinking long term over years of healthy training, not be trying to build up to your maximum possible distance in a very short period. Incidentally, to be most effective these long runs are continuous runs, not run/walks. If you need to walk, then you are being too ambitious and should set shorter distances as your target, or run slower from the start, until you are comfortable with continuous running. This will help you both physically and mentally.

Increasing your long run distance should not be done in a rush. An increase of total weekly volume of 10% for a maximum of three weeks is quite enough, you should then stay at that level for several weeks until your body adapts. Think of how many weeks it takes to alter a golf swing, or recall when you learned to drive and how long it took until it became natural behaviour. Adaptation typically takes 6 to 8 weeks.

The intensity of your long runs matters. They are not completely leisurely jogs but neither are they long sprints. If you have competed in 10k races, then you will have established what your 10k race pace is and can use that to calculate your guide pace for your long run. Go for a pace that is about 25% slower than your 10k race pace. (For example, if your 10k race pace is 5:10 min/km, pace your long run at 6:22 min/km). Even better is to start your long run at 33% slower than your 10k pace, increasing pace to 20% slower than 10k race pace by the end. (For example, if your 10k pace is 5:10 min/km start at 6:47 min/km and end at 6:07 min/km). The recovery day following your long run day should be resting or cross training, but not running.

If you have not yet competed in 10k races, or do not wish to, then a simple guide to your long distance run pace is to think about how you talk when running. You should find it Easy to talk and Easy to run for the whole distance. See table below. If during your long run, particularly as you tire, you are feeling out of breathe then slow down. Keep it Easy to the end.

Description of run pace





Perceived Exertion

Very easy


Just comfortable


Breathing reference

Very easy to talk in long sentences

Easy to talk

OK to talk in short bursts. Periods of silence

Hard to talk. Staccato

When you start your long run, or any run for that matter, the glycogen (carbohydrate) stored in your muscles and liver is the source your energy systems use to power you along. The principle energy system that will use your glycogen is your aerobic energy system. It is the key energy system for endurance running; aerobic meaning that oxygen is required.

The more quickly you run compared to your average pace, the more rapidly your glycogen stores will deplete. Run quickly and your body then thinks you need more energy quickly and switches on your fat stores as second energy source for your aerobic energy system. However, fat stores need much more oxygen to convert it into energy than your glycogen store.  So as you rapidly switch over to use more of your fat stores, you rapidly need more oxygen, so you will breathe heavier, get out of breath and then find it hard to recover unless you change your run to a really slow pace, or walk. Once you have switched on the use of your fat stores to create energy, it is really not possible to switch them off until you stop. So your plan should be not to suddenly switch on yout fat stores, but to bring them on line slowly.

Gently introduce the use of your fat stores by slowly using your glycogen stores. Your body does not then think it suddenly has to create more energy rapidly and so when it begins to use your fat stores it does so gently, putting less demands on your oxygen intake. You will do this by running at a slower pace than you think you should! Dont be suprised if you are not out of breathe at the end of your long run. Your legs might be tired, but you might breathing almost normally, which is good. (If you are running in a group you will naturally want to keep up, but the pace might really be too fast for your needs.  Be warned and slow down!)

If you increase your weekly distance too quickly, you will not have given sufficient time to develop your body so that it uses your glycogen stores as your desired energy supply to your aerobic energy system and will find it hard work. 

This is a good article by Runners World on this subject. How running slower can speed you up

By the way, if your aerobic system is not well developed, you won’t burn much fat before fatigue, so you will tire even more quickly.  It takes time to develop your bodies aerobic energy system and its use of glycogen and fat, so make your long runs slow and steady and regular, building up distance bit by bit. Don’t be tempted into running faster because you feel good; you will be losing the benefit of your run.

Graeme Loudain – September 2019

These notes are published as a general aid to all endurance runners. They are guidelines based on current best practice, intended to illustrate the points in the articles rather than provide a precise training schedule. They are written in a way to be of help to runners. Individuals will have their own requirements and the content of the notes will not suit all. Please use them in the spirit in which they are intended and modify them to suit your own needs. If you have suggestions for improvement, amendments or comment, please email gladmin@btinternet.com.