Is it Time to say Time goodbye?

When we talk intervals, we talk about a fixed time-on and fixed time-off. But are fixed time intervals really that good?

In order to improve our athletic performance we need to ‘extend or intensify’, as nicely stated by Dr. Seiler. This basic statement already indicates that 4 times 2 minutes, 4 times 4 minutes or x times y minutes, is not the proper answer to our improvement goal.
If we can do 4x2 today, we should try 4x2.1 next week as per the overload principle.
So who are we fooling with ‘fixed time intervals’?

The history of time based intervals may be found in several factors including the availability of stopwatches and non-availabilty of heart rate monitors, lactate meters and other fancy stuff that measures the effect of the duration.
But times have changed and so has our knowledge on how our bodies respond to loading and unloading.

We now know that the duration of the work bout has an effect on the amount of stress we produce for our bodies. We also know that there is a big difference between energy replenishment (within minutes) and muscle hypertrophy (hours to days).
Actually, we already knew that long before people started researching those topics. Our bodies came with a built-in health meter. We just need to listen to it.

To properly translate our improvement goal to interval training, we need to:

  1. define the goal of the interval training
  2. determine the proper duration
  3. extend the duration

Defining the goal is about choosing between strength (capacity) and endurance (power).
To improve strength / speed / sprint, we need intervals where we unleash a lot of energy, i.e. at least more than 50% of our 1 repeat max (“1RM”).
To improve endurance / increasing average power output, we need to apply the same strategy, but now to the heart.
Please note that the endurance intervals might be as hard on the muscles as the short intervals. So proper damage assessment after the interval session is required to plan the next session.
Therefor it is a good practise to alternate between interval days and low-intensity days, because the DOMS will reveal itself only after 24 hours.

Determining the proper duration is all about testing our current capability and then extending it after we have super compensated or determined that it was too easy.
To prevent injuries we better start close to what the athlete estimates is doable. This can be any duration and any number of repeats.

Whatever values one chooses for repeats and duration, make sure the values are higher the previous ones. Because that is what extend means.

So when we prescribe intervals, don’t just say 4x8. It is never the right prescription.
Instead: Plan, Do, Check and Act.

Hi @kjeldbontenbal (welcome to the forum).

Where does intensity fit into your statement?

Duration could remain the same, but intensity increase by a few percent (of FTP) and you should see a different result that doing the same duration and intensity as before.

A far as I have read, and listened, the workout planned would target an energy system, which has a range, eg. VO2max is 106-120%.

So if I start with a 4x4 workout and try “target” 106%, then surely 110% (next time) and 116% (the week after) is as good as lengthening the interval duration, or the number of intervals?

I’ll probably annoy Trevor by saying target 106%, as I could feel refreshed and decide to push closer to the upper limit of the VO2max level, or drop to 106% if I’m not feeling totally refreshed.

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Ah, good point Gerald.
I should have added that the intervals targeting the capacity of the heart are at 90+% of HRmax.