Intervals (repetitions)

Interval training is a distance workout of faster repetitions, usually run well above your maximal steady state and your lactate threshold, with a recovery interval between each. The aim is to do enough “tiring, exacting work” (as Lydiard referred to it) to lower your systemic (full-body) pH as much as possible without the workout being so fast that local acidosis in your legs stop it prematurely (i.e. “your legs go from under you”).

Your aerobic conditioning and lactate threshold has been trained in earlier phases because their adaptations take the longest to build but their benefits remain for longer. Anaerobic capacity can be build within 4-5 weeks but must be maintained or it will quickly whittle away. In any case it depends on how fast and how often it is performed.

“Anaerobic capacity can be developed to its maximum very easily with various types of work which do not need to be rigidly controlled; it is simply a matter of the athletes tiring themselves with anaerobic exercise and stopping when they feel they have had enough.” – Arthur Lydiard, Running with Lydiard

Never commence this form of workout without a solid endurance base. Without this conditioning any intervals in your program are not worth the paper they are written on.

You can improve your recovery from intervals during the stamina phase of training by introducing a morning trot on the days when you have an interval workout (so do a short trot of 20-30 minutes, or 6-8k for elites, in the morning and the interval session in the afternoon or evening).


    1. Start out with doing a good warm-up. This is the phase during which to develop and practice your own pre-race warm-up.
    2. Choose a distance or duration that you feel comfortable repeating. (For examples, see the chart below.)
    3. In-between each repeat take a recovery trot or walk  interval of the same duration OR until your heart rate comes down to your long run range (for instance, if doing 1k reps at 3min/km pace, run easily for 3 minutes in between)
    4. When doing very fast (1 mile pace and faster repeats) take complete recovery or easy walk (e.g. no trotging) until your heart comes comes down to around 100
    5. As each week passes, you can reduce your recovery by 5-10 seconds but consult with your coach around this

Stop the workout when:

  • You start to struggle to hold your pace
  • Your time starts to fall off
  • You cannot hold good form
  • Your workout is completed

Make sure you finish the workout with a good cool-down; minimum of 15 minutes easy trot. This will aid your recovery.

Important points:

  1. Never do this type of workout 2 days in a row.
  2. Always give yourself at least 48 hours to recover.
  3. Check your recovery indicators daily. Do not do another interval workout until you have recovered from the previous one.
  4. Never run intervals if you feel an infection coming on.
  5. Never do more than one interval session at hard anaerobic pace (explained below)

How to progress interval training

To minimise risk of staleness and injury progress your interval training through the following three phases (the workouts in our programmes automatically factor this transition in):

  1. Preliminary anaerobic: a transition between aerobic work and hard anaerobic work. Run these intervals not much faster than your lactate threshold and trot the recoveries for maximal circulation and lactate clearance during the workout. Generally run at paces between 5k and 10k race pace.
  2. Hard anaerobic: builds buffers against lactic acid to tolerate the fastest paces and supports strengths, biomechanical efficiency and power. Generally run at paces close to 3k-5k race pace and with shorter but full recoveries (standing or light walking).
  3. Glycolytic anaerobic: increases VO2max and serves as pecialised training for middle-distance runners at the anaerobic paces equal to a runners 400 to 1 mile race pace.

Rate of perceived effort:

7-9 (90-98% VO2max) or 10 (100%-130% VO2max)

Experienced competitors/elites:

Extremely conditioned elite runners can handle anaerobic volumes in excess of the 7km maximum which the standard programmes prescribe as maximum interval workload. Hicham el Guerrouj, the 1500m, 1 mile and 2000m world record holder, regularly employed sessions such as:

  • 4x2000m with 2-3min recovery at faster than 5k race pace.

Because el Guerrouj’s 5k race pace is 2:34min/km (4:08min/mile), he will only spend around twenty minutes at anaerobic speeds. Very fast competitors are thus better off going by time than kilometres when gauging whether the anaerobic load is appropriate and African runners in particular have much larger aerobic base conditioning to build their anaerobic workouts on.

“You should understand what you are trying to achieve with anaerobic training and work accordingly. In this system of repetitions, you run until the oxygen debt incurred makes you feel tired, indicating that you have developed a low blood pH. The times of the repetitions and intervals, the number of repetitions, and the distances run are not really important.” – Arthur Lydiard, Running the Lydiard Way

Experienced and elite middle-distance runners will need to perform certain interval sessions well above VO2max including workouts at 1 mile race pace and faster. The middle-distance athlete’s body needs to tolerate the very fast rates of local acidosis that they will experience in their target races. This is called glycolytic anaerobic training. We explore this further under variations below.


  • Anaerobic glycolysis:
  • Tolerance to oxygen debt
  • Lactic acid metabolism
  • Efficiency at faster paces


  • Developing a “comfort” level to the discomfort of oxygen debt
  • Pace judgment

Biggest mistakes:

  • Converting your training times to predict race times. Your times will probably not correlate to race times as yet simply because you have not yet developed your speed to its maximum. The times are not important it is the physiological response of your body to the workout that matters.
  • Cutting the recovery trot too short. As a result you may have to end the workout prematurely and/or you won’t be able to run the repetition fast enough. For optimal training benefit aim to fulfill the prescribed volume of this workout as best you can. You don’t want to recover completely but you want to be pleasantly stressed.
  • Squeezing out one more repetition after the signs to quit are evident. This is counter-productive and will mess up your training for the rest of the week. Have the discipline to stop pouring when the glass is full.


An athletics track is ideally suited for interval work as it allows you to focus solely on the paces and aids consistency and pace judgement. Grassy fields, sports pitches, hard trails and similar surfaces also support excellent interval sessions especially if you run by time rather than distance. Cross-country runners should go out of their way to perform intervals over cross-country courses. Mountain runners and other off-road runners regularly perform intervals on ascents and descents as part of a specialised type of interval training called hill repetitions. For purposes of brevity we elaborate on this variation in a separate article.


Glycolytic anaerobic intervals: the energy demands of middle-distance events (800m-2000m) are enormously different from those of longer distance events. Once an experienced middle-distance runner has phased himself into interval training with workouts around VO2max pace before moving onto workouts at his 1500m and then his 800m race pace.

A few brief workouts at this pace is sufficient to have all systems firing. Workouts at 1500m pace should generally not exceed 3.2km (2 miles) in total and should include a number of minutes recovery (i.e. 8x400m). Workouts at 800m pace should total no more than 1.6km (1 mile) such as 4x400m.

Athletes concentrating on longer distances should not consider such high-end workouts as they will come at  significant cost of aerobic capacity.

“Small total workloads of very fast glycolytic running (800m pace) will yield terrific training response if the preceding work has been done correctly and full aerobic recovery is taken. If the preceding work has been achieved haphazardly, then the training response may be a very tired or injured athlete.” – Dr Keith Livingstone,  Healthy Intelligent Training

Mixed intervals: mixed intervals are similar to normal intervals except that the distance covered during your fast repetition changes: instead of 4x800m, your workout could consist of 2x1k, 1x800m and 1x600m. Normally when you run intervals you should focus on running at one steady pace every single repetition and from repetition-to-repetition.

There are two main types of mixed intervals: the “staircase”, starting as short intervals and moving up (1x200m, 1x400m, 1x600m) and the “pyramid” (1x200m, 1x400m, 1x200m). Staircases can be either “ascending” or “descending” depending on whether you want to start slower or faster. Apart from that no real set format exists but coaches often bring these sessions out simply to add variety and spice to a training programme or, perhaps, as Peter Snell memorably put it in his 1965 autobiography “No Bugles, No Drums”: “to justify their existence”.

He has a point and generally normal intervals will give you a more consistent workout. For off-road runners this workout does offer increased race specificity because you will be running at slightly different anaerobic paces throughout and with shorter and longer recoveries. This mirrors the type of stress experienced when running hard over undulating and varying terrain.

Intervals with a twist: small variations in the set rhythm of an interval can be introduced, especially late in training, to mimic some scenario you expect to see in a race or to “squeeze” in a bit more training without risking overdoing it. A good example is adding a 200m repeat after a set of longer repeats. This could either mimic having to put in a fast finish during a race or simply be a shorter repetition to finish off on (for instance, if you do not feel like running another 800m but still believe you have a bit to give on the day).

Hills repetitions: this consists of repetitions done while running uphill, downhill or a combination of both. This workout requires the athlete to have greater leg strength to be successful and offers a more specific workout for mountain, fell and other off-road runners. We have dedicated a separate article to this variation.

Parts of the workout descriptions are adapted from BreakThrough Running with permission.

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Director and coach at Borg Coaching Services
Rene Borg is the head coach of Glendalough AC and a passionate runner competing over all distances and terrains.

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