Training: Intervals

This article, in our series of training articles, is focused on Intervals.

In the previous article we looked at the long run, as this is the run most people focus on first when they want to improve their running. As discussed, long runs are very important, but they are not the be-all-and-end-all. Improvement in running (for the purposes of these articles we’re taking that to mean running further or faster) is the product of a balanced training plan that covers all the energy systems and physiological requirements relevant to your goals in your chosen event.

Run faster to run faster

It is not uncommon for new runners to improve their times quite quickly, then plateau. This may be because they have solely focused on increasing the distance they run for. This improved endurance is enough to get them over a parkrun finish line, and then start reducing their time, before they get stuck – always finishing within a few seconds of their personal best (PB), but no longer making big gains. This is despite them feeling stronger and more efficient and capable of running far further than when they first set their PB.

This may occur when all their running is done at one speed. They can keep going for ages, but cannot speed up. The solution to this is simple. If you want to run faster, you have to run faster. And one of the best ways to do that is to incorporate intervals into your training.
To an extent, if you are currently doing no speedwork whatsoever, then anything you do is likely to yield an improvement, regardless of the form that faster running takes. The difficult thing is working out what speedwork you should do and how to fit it in to the rest of your plan. There is no set formula and a practically infinite range of possibilities.

How to incorporate speedwork into your training

As with all parts of a training plan, we need to consider what we are trying to achieve, what it will take to do so, and tailor that approach according to our circumstances. To illustrate this, let’s consider the example runners from our article on long runs.

Andrea – looking to run her first marathon

Her main focus is, understandably, her long runs, but speed shouldn’t be neglected. Andrea knows that by the end of the marathon she’ll be very tired and her running form is likely to go to pieces. By doing hill sprints – which build muscular strength – throughout her plan she may be able to retain her form for longer. Also, sprinting will develop her ability to recruit all the muscle fibres she needs in the marathon.
Our muscle fibres can broadly be categorised into two groups: slow twitch or fast twitch. The differences are complex, but to generalise, slow twitch fibres don’t contract as quickly, but can keep going for longer. Fast twitch contract very quickly, but can’t do so for very long without a rest.

When running slowly, our bodies predominantly use our slow twitch fibres as they’re more efficient for moderate efforts over a long period of time. By the end of a marathon, however, the muscle damage may be so great that a lot of the slow twitch fibres are not at their best. Research suggests that if we’ve used our fast twitch fibres in training, by sprinting, our bodies will become more comfortable with cycling them in and out – even when doing slower running – to reduce the burden on the slow twitch fibres.

This is an oversimplification, but the general principle is that if we’ve used the muscles in training, we’ll be better able to use them when racing. Andrea doesn’t need to do too much of it, as marathons are mostly slow twitch affairs, but one session a week with half a dozen short sprints up a gradual hill, with long ‘walk back down’ recoveries between sprints may be sufficient for her.

The other kind of faster running that Andrea could consider is tempo or threshold runs, but they’re the subject of another article, so I won’t go into them here.

Balthazar – beginner doing Couch to 5K

Balthazar will benefit from speedwork for much the same reason as Andrea: to condition his body and prepare his muscles for running. Many runners spend time at the gym doing exercises that resemble actions performed when running: leg extensions, calf raises, squats, arms exercises, and work on the core muscles, etc. These can be beneficial, but it is worth remembering that no exercise will more closely resemble running than running itself.

Running can be thought of as a compound exercise (one involving multiple muscle groups performing different movements), in which the athlete does around 150-200 low intensity repetitions every minute, for minutes at a time. It is hard to replicate that in a gym.

Sprinting is a great way of taking that compound exercise and increasing the intensity. You are likely to perform more reps per minute, moving your muscles through a wider range of motion due to the higher cadence (steps per minute) and longer stride length and higher arm swing when sprinting. By sprinting uphill, you then add a further element by introducing more resistance as you have to overcome gravity, lifting your body up slightly higher with each step.

For a new runner like Balthazar, hill sprints can therefore be a great way to condition the body for running. A word of caution, however: the high intensity nature of sprinting can cause muscle strains and other problems if you’re not used to it or warmed up properly, so always ease into any sprinting session and take it easy or stop if something hurts.

Claudia – ultramarathoner training to run a fast mile

Claudia’s speedwork will look a little different. In addition to hill sprints for conditioning, she also needs to prepare herself for the challenge of running as fast as possible for a mile. This will require getting used to running at mile race pace. This is a hard pace to run at for an extended period of time, but Claudia will be able to build up the duration she can manage by running interval sessions. This is where you run at a hard pace for a set distance or time, stop or slow down to recover, then repeat the process.

There are practically an infinite number of ways this can be done, depending on the number of repetitions (the fast sections, often abbreviated to reps), length of the reps, speed of the reps, and the amount of recovery in between.

A good target to aim at is to cover the race distance or longer at the goal pace or quicker, with as few breaks as possible. Over the course of the training plan these interval sessions are likely to get progressively harder as Claudia’s fitness improves

An example interval session progression

Claudia wants to run the mile in around 6 minutes and is able to do her speedwork on a 400m long athletics track (a loop in the park would work too – a track isn’t essential – but it does make the maths easier for this example). With this in mind, her interval sessions over 7 weeks prior to tapering are as follows:

  • 8 x 200m run at 6 minute mile pace, with 60 second recoveries (walking around to stay loose and letting her get her breath back);
  • 10 x 200m with 60 second recoveries;
  • 6 x 300m with 60 second recoveries;
  • 5 x 400m with 90 second recoveries;
  • 3 x 600m with 2 minute recoveries;
  • 4 x 500m with 60 second recoveries;
  • 2 x 800m with 90 second recovery;

The last session will be really hard, and Claudia won’t be able to do it at the start of her training plan. However, by starting with something more manageable, with shorter reps, she can build up as her fitness improves.

The above is an example progression, but there are other ways of changing the variables to make the sessions gradually harder from an achievable starting point.

Changing the variables

Claudia may choose to run 2 x 800m with 90 second recovery for all of her interval sessions, but with the first one done at whatever pace she can manage – even if that is slower tan target race pace – with the aim of getting faster as the weeks go on, until she can run the fast bits at race pace or quicker.

Another option would be to do the 2 x 800m at race pace, in every interval session, with as much recovery inbetween as is necessary to complete the session. This might be 10 munute of rest between reps in week 1, dropping down as Claudia gets quicker until it is around the 90 second mark.

These options serve as examples of the three ways in which speedwork sessios can be made progressively harder and event specific over the course of a training plan:

  • By extending the length of each rep;
  • By increasing the speed of each rep;
  • By reducing the recovery between each rep.

It doesn’t matter which method you choose, but you may have an idea which option you are likely to benefit from the most based on you running history. The option you like the look of the most is probably the one you would find easier. On the one hand, that’s good, as you are likely to get the hang of the session quickly, which can be motivating. On the other hand, it can be better to do the sessions you find hardest and don’t look forward to, and go outside of your comfort zone and develop skills you might otherwise neglect.

Mixing things up

The best approach is probably one that combines a mix of the three different options, perhaps on a three-week cycle to keep things fresh. For Claudia this might mean:

  • 8 x 200m at 100% of race pace with 60 second recoveries;
  • 2 x 800 at 85% of race pace (ie: slightly slower) with 90 second recoveries;
  • 2 x 800 at 100% race pace with up to 10 minute recovery;
  • 4 x 500 at 100% with 60 second recoveries;
  • 2 x 800 at 90% with 90 second recoveries;
  • 2 x 800 at 100% with 5 minute recoveries;
  • 2 x 800 at 100% with 90 second recoveries.

These are just examples and I’d encourage you to work out your own personal combinations.


The examples above are fairly structured, but it is also possible to run unstructured interval sessions, known as fartleks. These can take whatever form you like, with faster bits of running broken up with slower bits. The pace doesn’t have to be precise either as you can run by feel – trying to maintain a high intensity without worrying too much about the exact speed.

Example fartlek sessions include using lampposts as markers – speeding up every time you pass a lamppost, then slowing when you pass another; or sprinting to the next street corner every time you see a car of a particular colour; or using other things on your run as markers or prompts to put in a burst of speed. This can be a fun way of introducing intervals to your training without the stress that can come from being too rigid with distances and paces. The unpredictability can be beneficial to experienced runners too, as it can break you out of your normal habits and provide a different stimulus.

Pros and cons

What are the advantages and disadvantages of interval training?


  • Improves speed;
  • Builds strength;
  • Improves form.


  • Can lead to injury or fatigue;
  • An overemphasis on speed can lead to endurance being neglected.


What alternatives are there to intervals? The answer is, not many. The usual cross training suspects apply – swimming, cycling, elliptical trainer in the gym – done in a high intensity interval manner. Particularly effective is simulating your running sessions on an indoor rower.  For example, if your running training plan calls for 10x 400m efforts, you can do the same exact same session when rowing.

You can also get some of the body strength benefits by doing weights work – especially squats and similar exercises. But as discussed above, only running can tie these together into one complex activity that is suited to running.


Speedwork – be it short sprints, fartleks, or structured interval sessions is an essential part of every runner’s training plan. If you’ve got limited experience of running at a faster pace, then it can be useful to hold back slightly at the beginning while your body adapts to the change in intensity. Once you’ve gotten used to it though, the jumps in your running performance can be considerable.

Click on the link for the next article in our training series, on the often-confusing world of tempo runs.

Join Waitlist We will inform you when this item is back in stock. Please enter your email address below.