Igloi intervals (misunderstanding intervals)

Today, interval training has become synonymous with hard training for the majority of runners. It is no wonder this type of training causes a bit of confusion as even the name is a misnomer. Often we will say ‘we’re doing intervals’ and we will think about the hard sections but the ‘interval’ in ‘interval training’ originally referred to the ‘rest interval’ (also the meaning of the word itself).

Leaving the name aside, it’s a bigger mistake to think of intervals merely as ‘hard’ training because they can be run at any intensity. Truly there are only two basic types of workouts: steady effort runs and varied effort runs. An interval session is varied effort because intervals of easier running or recovery break up faster sections. This basic format has spawned countless specific session types such as alternations, lactate shuttlers, cut-downs, Fartlek, cruise-intervals, tempo-intervals, and many more. Steady effort runs are the opposite – runs with the intention of maintaining even pace or effort throughout. In reality even steady effort runs do not truly exist because you can never hold the EXACT same pace all the time – there’ll always be some variation. But it’s the intention that counts here.

Igloi intervals are an example of intervals that are not necessarily hard but that can serve a different purpose than traditional intervals. First a bit of back story:

A problem to solve

In the recent year I have – with some success – tried to break what I call my ‘pace rut’ which is basically finding it difficult to do the hero workouts of my glorious 2012 season where I seemed I never trained as well as that year neither before nor since. The challenge is that recreating the circumstances as they were do not work because we are always operating on shifting sands – our bodies change and it takes more and more to make them respond with a training reaction. A beginner can be coached by just about anyone or do just about any training plan and they will improve. The seasoned runner often hits a point where nothing seems to make them truly better. There is so much paint on the canvas that nothing new seems to stick.

You can attack these problems from many angles and you don’t have any option but to simply try – you cannot intellectualise yourself to the root of the problem. All we can know for sure is that because human beings are complex dynamic systems, then we also know that they operate within constraining forces and bottlenecks. A limitation in one key system may be preventing all other systems from moving on. The best example is injury or illness: once present it is often impossible to get the body to adapt beyond a certain point because the injury restrains the adaptations. But it could be anything: the strength of your breathing muscles, your running technique, the way you eat, the stress level in your life or the more classical culprits – the aerobic and anaerobic systems.

I tried first to repair the aerobic system to see if this would bring paces back up. I noticed eventually that extending distance was easy enough but it only had a small effect on average pace. I could easily go out and run all day (as I did during a trail running holiday) without feeling one bit tired at the end as long as it was slow. So I threw strides and power training at the problem again with some positive effect – race performances were slightly better this year than previous ones and my 100m times began to drop again. But average training pace did not yet improve much which is what you’d expect because there needs to be some kind of transfer mechanism between very general work (long and slow or very short and very fast) towards the middle (medium work, medium speed). It does not magically ‘just happen’, in most cases. Enter Igloi intervals.


Mihaloy Igloi utilised a format of interval training with many short repetitions interspersed with very short rest intervals done at various paces which were described through subjective statements such as ‘easy’, ‘fresh’ and ‘fast good’. Without going further into details about his method (others have done this far better elsewhere), you can make it work for you by selecting a very short interval (I opted for 150 metres) which you aim to run at the pace you’d like to restore as your ‘default’ – in my cause the 4:40-4:50 min/km pace I used to be able to hold for 90-120 minutes no problem even over undulating courses (that’s a 42 second 150 m). The recovery is a 50 metres float, very easy. Since Monday is my recovery day and I had decided I really needed it I confined myself to a very short 4 km run (20 x 150m, 50m float). So the session was:

  • 20 x 150 metre repetitions with a target of 42-43 seconds
  • 50 metre active floats with no target

I wanted to keep this aerobic (recovery run after all) so put my heart rate warning on to ‘beep me’ at 143 bpm or higher. The way I imagined the run I would be able to run longer total time at ‘better paces’ without pushing my heart rate into the ‘steady’ zone (which would have made the run a short easy tempo). Keeping in mind that the road outside my house is very hilly, I knew some reps would be a bit slower and to go by feel in those cases. So how did it pan out? The graph below show it:

pace dsitribution

Basically of the 20 minutes run only 4 minutes were slower than 5:19 min/km pace and I also got about 2.5 minutes at paces from 3:37 to 4:35 min/km. The heart rate did not run away on me doing this: the average was 142 beats per minute with the highest 153 bpm.

I had managed to peak at 54 VDOT performances for my three target races this year: the Wicklow Road Championship, the Wicklow Way Relay and The Relay. But most of the year I had hovered around 48-51 with my best level in 2012 being 58-60 (despite bizarelly having been measured with a VO2max of 78 in a laboratory – an engine whose potential has never shown itself in an actual race likely due to other constraints). After the recent race I had dropped to 49, recovering to 51 by this weekend’s session. This run immediately jumped it up to 52. Did I suddenly get fitter? Unlikely, but rather it shows that this workout type gave me a better relative pace for the average heart rate – so overall a better workout than had I just gone out and run 142 bpm average for the whole stretch (although I should really do that now to prove my words!).

A few weeks ago I covered an Out and Back over 6.1 km (so 50% longer) at a pace of 5:14 min/km with an average heart rate of 151 and higher maximum heart rate (today’s pace was 5:00 on average at a heart rate of 142). So I was 14 seconds faster per kilometer for 9 beats of my heart less per minute. The 6 km course is a bit hillier than the 4 km but Grade Adjusted Pace was also better at 4:59 min/km versus 5:09  min/km (so 10 seconds faster per kilometer adjusting for hill differential). Interestingly in the longer run I never got down to paces as fast as 3:37 min/km. So what does all that mean?

Outcomes and how you can use this


  • Igloi intervals can give you a better run in terms of overall quality of paces your body experiences
  • Igloi intervals can give you this increase in quality while putting less metabolic load on the body

Essentially, it is a way to extract ‘more time’ at certain paces at lesser cost by using small recoveries to extend the time you can maintain these paces. So how do you give it a try?

Here are the steps:

  1. Pick the pace you’d like to make your standard training pace again (or the pace you’re looking to get better at for other reasons)
  2. PIik a very short interval that you’re confident you can run this pace at without your heart rate going crazy (often 50m to 250 m will do)
  3. Pick a very short recovery period, preferably one that makes it easy to remember (for instance you could do 100 m on/50 m off, 150 m on, 50 off, 200 m on, 100m off, 250 m on, 150 off etc.). But there’s no hard and fast rules – the recovery should be just long enough to get a small bit of breath back – but be warned 50 metres goes by very quickly!