Methods of Endurance Training Part 5: Interval Training Part 1

Having looked at threshold training in Methods of Endurance Training Part 4: Threshold Training, I want to wrap things up by looking at interval training, since this represents the final major method by which endurance athletes (or athletes who need some form of endurance) typically train.

As usual, I’m too wordy for my own good and this is going to be a two parter since interval training has relatively more to cover than the other methods I’ve discussed.  Today will be more of an introduction to some important concepts and definitions regarding interval training.  On Friday, I’ll wrap-up by looking at some of the potential adaptations and applications generated by interval training.

I’d mention that, I’ve written about this topic rather extensively, on the site previously, readers may wish to read Steady State vs. Interval Training Part 1 and Steady State vs. Interval Training Part 2 along with the monster series I did which starts with Steady State vs. Interval Training: Introduction.

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By Way of Introduction

Over the years interest and use of interval training with endurance athletes has gone through it’s ups and downs with relatively more or less emphasis placed on it.  And certainly, there are both pros and cons to interval training which is why, like all methods, it has its place in training.

Relevant to this article series, the paper I linked out to in Methods of Endurance Training Part 4: Threshold Training discusses, the training of elite endurance athletes these days currently utilizes a very small amount of this type of of high intensity work, perhaps 4-7% of the total annual training volume across a wide variety of pure endurance sports.  This is in some contrast to the current Internet fad/belief that intervals are not only a superior way to train but almost the only way anybody should ever train.

Certainly, some lines of current research do support the superiority of interval training for some applications (I’ll come back to this below).  However, the whole pro-interval trend is reaching what I consider a ludicrous extreme with claims that steady state work is not only useless to performance (a belief clearly contraindicated by the real world) but actively detrimental to performance (also not consistent with real-world results).

As is so often the case with extreme viewpoints, the truth lies somewhere in the middle.

A point I’ve tried to make throughout this series is that the types of training undertaken by elite endurance athletes are great when you have 20-30 hours/week to train.  And start to become marginally less useful when folks have lives, jobs, families and can’t train at that level.  When the amount of training available decreases, the methods often have to change to some degree.   I’ve discussed methods such as tempo training, sweet spot training and threshold training in previous parts of the series; ways of getting a similar training effect in a reduced amount of time.

As well, to make the point again, athletes who need endurance as one of their performance characteristics don’t generally have the time to spend on purely long-duration endurance work; they have too much else to work on.  At the same time, they don’t generally have the requirements for endurance seen with endurance athletes.  So they wouldn’t need to put in that many hours in the first place.

And with that out of the way, let’s look at interval training.

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Defining Terms

Interval training can actually refer to a staggering number of different types of training.  Very generally speaking, interval training refers to any sort of training where harder bits are alternated with easier bits.  In fact, weight training could be considered a form of interval training and, certainly, there are methods of conditioning that rely on weight training (or some type of non-cardio modality such as sandbags, sleds, or what have you) used in an interval fashion.   For the purpose of this article, I’m going to focus primarily on more traditional modalities of endurance training as used by endurance athletes (e.g. cycling, running, rowing, etc.).

Of some historical interest, when interval training was first invented or developed (and note that this was back in the earlier part of the 20th century; interval training is by no means ‘new’), the focus was actually on the rest interval as it was thought that that was the cause of the adaptations.  At the time it was thought that interval training primarily affected heart function and it was the rest interval which forced the adaptation to occur. I’ll come back to adaptations a bit below.

Interval training can be defined by a number of different variables including (but probably not limited to)

  1. Intensity (relative to some metric, be it VO2 max or the lactate threshold)
  2. Duration of the work interval
  3. Duration of the rest interval
  4. Number of repetitions performed
  5. Number of sets performed
  6. Rest interval between sets (if more than one is being) done

For example, the 2X20 threshold work I described in Methods of Endurance Training Part 4: Threshold Training might be described as 2X20’/10 rest at 100% of functional threshold.  The duration of the work bout is 20 minutes, the rest interval is 10 minutes, two repetitions are done and the intensity is right at 100% of the threshold.  This can get as complex as you want it depending on what’s being done.  Although I still don’t claim to understand the training on any level, swimming seems to take the prize for the most complex interval schemes of all the sports.

Now, I should note that, strictly speaking, low intensity work (relatively aerobic work) can be done in interval style.  For example, rank beginners often can’t perform even 20 minutes of continuous low intensity activity, they might actually perform 4 sets of 5 minutes at an aerobic intensity with a short break building up eventually to 20 minutes (or more) of steady state work.

As another example, short sprinters often perform a workout usually called Extensive Tempo training (not to be confused with the tempo training I described in Methods of Endurance Training Part 3: Tempo and Sweet Spot Training).  This can be done a tremendous number of ways but typically intensity is set at 75% or less of the best speed over a given distance with run distances from 100-400m and fairly short rests used with a moderate to high volume of training being done.  The idea is to generate a pseudo-aerobic/conditioning effect without having to slog the miles that tends to cause injury or hurt sprint speeds.

However, I’m not going to discuss the above types of interval training here.  Rather, I want to focus on what is commonly called High-Intensity Interval Training (or HIIT) since that is where the majority of interest and focus tends to be these days.  In HIIT, the work bouts are invariably short (ranging from 15-20 seconds to maybe 5 minutes as an absolute maximum) and the intensity is going to be above the ‘lactate’ threshold (all the way up to VO2 max or beyond).

I’d note that, in contrast to other parts of this series, I won’t be talking about heart rate responses relative to HIIT.  This is because heart rate response becomes fairly useless for HIIT.  The problem is lag, it takes heart rate 3-5 minutes (on average) to reach a steady state and with intervals shorter than that, heart rate simply isn’t useful.  At best, if someone is doing repeats of a certain interval duration, heart rate will eventually climb up to a steady state.  But over the first few repeats, heart rate won’t tell you much about how hard the person is actually working.

Rather, intensity is usually set relative to some other metric.  In the power meter community, various intervals are done at some percentage of functional threshold power (e.g. 110% of FTP).  In running, usually time per unit distance or race time (e.g. repeats at your best 3k time) are used.  Others simply recommend ‘working at the highest intensity sustainable’ for the entire duration.

So if you’re doing 3 minute intervals, you try to select a workload that you can sustain for the entire period (rather than going out too fast and dying at the end).  This is often a problem for folks new to training, they have no clue how to pace and end up going out way too hard initially and then die on the vine.  It takes practice to know what sort of intensity can be maintained maximally for a given duration and beginners rarely have this pacing ability.

I’d also mention that while intervals are commonly set in terms of duration (usually chosen to achieve specific physiological effects), this isn’t universal.  Many sports, usually those involving training around a set distance (e.g. running track) more often set intervals in terms of some distance.

So you’ll see 400m repeats on the track at a specific pace with a specific duration of rest (or something like ‘rest by walking 200m).  So the workout might be 3X400m@62 seconds (or whatever) with an 800m walking rest.   Sports such as road cycling or cross country skiing, where the focus is more on duration are more likely to set interval workouts relative to time.  So you’ll see 6X3’@VO2 max/3′ rest or 8-12X1’@110% FTP or something along those lines.

There are still other options, sports such as swimming often work solely off the clock.  So an athlete will be given a certain set of repeat distances where they start each repeat on a certain clock time (e.g. 2 minutes).  Speed skating will do this too and since I have more of a clue about that type of training than swimming, I’ll use that as an example.

So you might see a workout of 3X800m on 2 minutes.  So you skate 800m (2 laps) as hard as possible.  And you start the next set at the 2 minute mark.  So if you finish the 800m in 1 minute, you get 1 minute rest. If you finish it in 1:45, you get 15 seconds rest (meaning that, in a sense it’s harder for the slower athlete).    When the clock hits 2 minutes, you go again.  And when the clock hits 2 minutes, you go the third and final time.  Then you lay down for a little bit.

But generally what you see is that coaches have figured out what distances are going to achieve the types of training effect that they want, they set the distances to hit a certain time frame.  Basically, it all ends up being about the same at the end of the day with coaches setting up specific workouts to achieve specific goals (usually making the athlete wish they were dead) based on the peculiarities of the sport.

And with that I’ll wrap up for today.  On Friday, I’ll finish the series out once and for all by looking at the three major applications of interval training in terms of adaptation as well as looking at intervals in general in the context of overall training content.

Read Methods of Endurance Training Part 5: Interval Training Part 2