There has been something of an ongoing debate online about the benefits of interval training over steady state training when it comes to endurance or cardiovscular training. The perceived wisdom over the last few years pushing things towards the idea that all you need to do is some form of interval training and that steady state low intensity work has no value. As with most things the answer is no where near as clear cut as this and both types of training have their merits and the evidence, as we can see in this excellent paper, rather than the internet chatter, does suggest that both should be part of a well rounded program.
Long slow distance running, or other activity, speaks for itself and the idea is that you are doing something easy for 45+ minutes. Interval training has been around since the early 1900’s and have appeared in various forms since, and probably before but they weren’t given a name. The Swede’s have been using fartlek (fart=speed and lek=play in Swedish)training since the 1920’s when Gosta Holmer introduced it there. The term interval training is attributed to a German, Waldemer Gerschler who coined it in the 1930’s. The use of various forms of interval training has been developed further since then to include a wide range of times, speeds and distances and some have been given names others not. The Tabata protocol being possibly the most famous and talked about version of interval training.
The Tabata protocol was developed with Japanese speed skaters and carried out on stationary bikes. In this example the program consists of a warm up and cool down with 8+ intervals of 20/10 seconds (work/rest) where the work rate is set at 170% of your VO2 max and are done to failure, failure being the inability to maintain the set cadence for the session. This may have a very short work portion, 4 minutes, but is brutally hard and is definitely not something to be done long term or too the exclusion of other forms of training. It should also be remembered that it was carried out on a bike and is very hard to duplicate the effects using other forms of exercise.
In terms of the adaptations that the two types of training produce, low intensity training seems to be best for optimising peripheral adaptations, that is those in the muscles being used during the activity, whilst the higher intensities used during interval training and tempo training allow for improved signalling for enhanced cardiac function and better buffer of the blood pH.
In the paper they look at elite endurance athletes and see that they use a split in their training of about 80/20 between LSD and HIT. So the bulk of their training is carried out at, for them, very low intensities with only 1-3 sessions out of 10-12/week done at intensities we see in correctly applied interval training or tempo and threshold work. Whilst comparing recreational athletes to elite ones can be problematic given on the one had it’s the persons job and the other something they do for fun when it was looked at it was found that the same ratio could be applied and be found to work.
When it was examined in the paper it was found that the biggest issue for recreational athletes was that they tend to fall into what they describe as an “intensity black hole” where the sessions are all done at pretty much the same intensity range whether they are steady state work or intervals. Essentially the easy work isn’t easy enough and the hard work isn’t hard enough to stimulate the desired responses they are looking to achieve from the individual sessions.
As an aside, though I have no evidence to back this up beyond my own experience and it’s not talked about in the paper, I suspect that the lack of variation and as a result lack of easy training days is one of the contributing factors in the high injury rate we see amongst recreational runners. The lack of contrast in the sessions results in relatively high overall intensity of the training week means that it is more difficult to recover overall. We also are less likely to see the improvements in running economy that can come from properly applied higher intensity work and as such this may also place greater stress on the musculature which again may contribute to the injury rate.
The type of hard work that is most appropriate can vary as well depending on the level of experience and abilities. A recreational runner with a 10k time in the 40-50 minute area might be better using their hard sessions to work in around the lactate threshold. With a limited amount of time to train per week and the stresses and strains of everyday life a session of a 5-10 minute warm up followed by a 15-20 minute effort at a pace they could sustain for 60 minutes then a very easy 10 minute effort followed by another 15-20 minute hard effort would be a very productive use of time, especially, and most importantly, if the other days are very easy. As the athlete get better and sees their 10k time drop into the 30-40 minute bracket other forms of intervals and forms of higher intensity training can be used as the athlete has the ability to benefit from them.
With multi sport athletes like triathletes then the 80/20 rule still applies to the whole training week not the individual events. All that this means s that you rotate the hard work across the disciplines as you see fit. One week may be a hard running and cycling session the next running and swimming or you might choose to do one hard session of each if your weekly volume is sufficient to keep to the 80/20 rule.
To finish it’s a long and some what technical paper but well worth reading through if you are currently involved in any endurance work or are thinking of starting it. It gives some great insights into how to structure a well balanced training program that will help you achieve your goals. In doing so you will give yourself the best possible chance to achieve your performance goals and remain injury free.