Interval training is a distinct type of intermittent training
Interval training is another category of intermittent training; a major one. The name "interval training" does not derive just from the fact that the workout permits recovery "intervals" between the periods of fast running.
The name comes from the fact that original designers, Gerschler and Reindell, used an interval of time that allowed only incomplete recovery.
They believed that an accurate and incomplete recovery interval stresses the runner more and more with each additional running period. Each running effort becomes more and more difficult as the workout continues.
They discovered that when training with an incomplete recovery interval, then the recovery became just as important as the running interval itself, if not more important! Here lies the essence of interval training.
The interval training method allows for short and equal recovery periods, but always aiming for incomplete recovery, and preferring an active recovery so as to ensure that complete recovery cannot occur.
Here we can see that interval training differs from repetition training in the format of recovery. Interval training mandates incomplete recovery, while repetition training does not. Interval training requires precise, accurate recovery interval periods, while repetition training does not.
Another interesting component from the early days of interval training as expounded by Gerschler and Reindell was that the average pace of the running interval was originally estimated from given percentages of the athlete's best effort for the interval distance. e.g.: If your workout is formed of 400m intervals, then the pace is based on some percentage of your 400m PB.
Repetition versus Interval Training
Many runners and coaches from any number of sports use the terms repetition and interval training indiscriminately and interchangeably, and usually with a different interpretation than the original one.
The question here is not whether the name of the training methodology is important, or whether the standard model should be changed, but our goal must always be to understand the exact goal behind the training.
Different training methods will stimulate the runner in different ways, and it is normal for training methods to evolve or be adjusted to different needs and contexts, such as tweaking for individualisation and personalisation purposes to suit the needs of each individual.
But if the training no longer provokes the adaptations conceived by the original concept, then it is no longer the same training, irrespective of the name used. It may appear to be related by name, but it is no longer the same training.
Interval training is different and distinct from repetition training. In repetition training, the pace is estimated from the target event. In interval training the pace is a percent of your PB for the interval distance (i.e. a percent of your 400m PB when running intervals of 8x400 indistinctly what is your goal distance event).
This original distinction between the two main intermittent training - interval and repetition methods - goes back to the two separate original concepts on which they are based.
In repetition training, the pace of each rep is calculated from the pace of the target event with a near-complete recovery (e.g. a 15:00/5k runner runs reps of 3:00 per km if done at 100% race pace, or 3:09 if done at 95% race pace, recovery is near-complete).
In interval training, the pace is calculated from a percent of the athlete's PB for the interval distance (e.g. a runner with a 400m PB of 55 secs would run 8-12x400 in 66 secs if running reps at 80% effort - multiply 55 x 1.2 = 66).