Hi Stephanie,
Maya and I would be more than happy to answer a few more questions regarding HIIT, or any intensity training in tomorrows zoom. We will be discussing use of TP’s CTL/ATL/TSB and other factors. The answer to your question is rather involved as we have to look at where the athlete is in their training, what the goal is, when the goal takes place, if they have ADS, etc. First I’d recommend reading or listening to the most recent book that Scott wrote it really dives into all the particulars and explains the what/when/how of UA philosophy which is reflected in these training plans.
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Another resource: the article below, I saved it years ago and the link to the website it was on no longer works so here’s the content below. It might help ( :
Sand Castles: A mental model of endurance training
March 22, 2018
Training endurance is like building a sand castle. You need sand and water, the sense not to overdo it, and the expertise to make something great.
Basic endurance is like piling dry sand. It can’t be shaped, just piled higher. For every inch of height, it takes a greater volume of dry sand than the inch before.
Adding intensity is like adding water. You can increase the angle of repose of the sand, steepening the cone, getting higher with the same volume.
Artists (great coaches) can get the saturation just right, creating amazing sculptures that will always be temporary.
HIIT proponents misunderstand the sand/water relationship, thinking that water is the big secret:
“If water makes sand piles steeper, let’s just use that!”; and
“If the pile of wet sand starts to crumble, add more water!”
The distinctions are:
First, it’s not either/or, but the mix of sand and water that’s important;
Second, wet sand is born from dry sand; it’s not independent. The volume of dry sand still determines the ultimate height of the cone or the shape of the castle; and
Third, if the pile starts to ooze downward, adding more water won’t help. To restore it, you have to dry it out (by adding more dry sand).
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The simplicity of slow twitch endurance
Slow-twitch muscle fiber is the main driver in long, easy training sessions. Slow Twitch Endurance (STE) can increase in two ways: 1) lengthen the duration of the demands on slow twitch muscle fiber; or 2) reduce the fuel available to those fibers. With either method, you need more of the same to create increases in endurance.
STE is a lot like very dry sand. It can’t be sculpted or shaped, only piled higher. The height of the pile is a function of the angle of repose and the volume of sand available. To increase the height of the pile, you need more and more sand.
Now imagine that pile of dry sand as a series of layers. Each layer is a hollow cone, one inch thick, nested one inside the other. Every one-inch cone must be of greater volume to fit over the previous one. Every one-inch increase in height demands a greater amount of sand than the prior inch required.
<Greater-height-demands-greater-volume.png>
Basic endurance training is like piling dry sand. It can’t be shaped, just piled higher.
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The fun of fast twitch endurance
Thankfully there’s a second ingredient that can boost the performance of STE: Fast-Twitch Endurance.
The second type of muscle fiber, fast-twitch, comes alive with intensity, but that intensity is short-lived. To bolster endurance, fast-twitch fiber needs to be forced to work longer than it wants to. Once recruited with a high load, the duration of work is extended, forcing the fiber to work aerobically.
Fast Twitch Endurance (FTE), the “water”, is exciting because it reacts quickly and the athlete gets faster sooner. It hints at a more-for-less opportunity: You can make the sand pile taller with the same amount of sand. The angle of repose of wet sand is steeper, so by adding water to dry sand, you can get an additional inch of height without adding more sand.
But trees don’t grow to the sky. Fast-twitch endurance development can’t be done on its own or forever.
<Add-water-to-dry-sand-to-make-it-steeper.png>
Wet sand has a steeper angle of repose, so the same volume of sand can be piled higher by adding water to dry sand.
—
What about sand castles?
To build a sand castle you need just the right amounts of sand, water, and expertise. Great artists (i.e. great coaches) can build sand castles, but they know that the castles are always temporary. The castles will eventually dry out, or wet out, fall down, and become a pile again.
In endurance training, building sand castles means getting the saturation of the sand just right. Then the sand can be shaped and sculpted.
<Add-water-and-expertise-to-make-a-sand-castle.png>
Dry sand plus water plus expertise is when things get interesting.
More water!
HIIT proponents see the benefits of intensity training, but not in the broader context of where those benefits come from. (From the mix, not the components.)
If they’re working with largely sedentary people with no aerobic foundation, that broader context is not so broad, so it’s effectively invisible. It’s a case of WYSIATI (What You See Is All There Is) that naturally leads to mistaken conclusions and overconfidence.
Bad Conclusion #1: “If water makes sand piles steeper, let’s just use that!”
Spoiler alert: You can’t build sand castles with just water.
The HIIT crowd assumes that intensity is a shortcut around more training volume. They force a false choice between dry sand and water, thinking (and espousing) that wet sand can be drawn from an outside source.
Although a pile of wet sand is steeper than a pile of dry sand, the wet sand can only be born from the dry sand. It’s not independent. So the ultimate height of the wet sand is still limited as a function of what it’s made from.
Intensity isn’t wet sand; it’s water. You can only make wet sand with water and dry sand. If you only have water, and no dry sand, you can’t make anything.
Bad Conclusion #2: “If wet sand starts to crumble, add more water!”
Because the addition of intensity (i.e. “water”) has so much immediate benefit, it’s often assumed that more is better. But just like a pile of sand, adding water helps, but only to a point. It makes the pile steeper, but too much water will turn it into an oozing puddle.
Because the choice between dry sand and wet sand is false, the HIIT crowd is backed into a corner. If adding more and more intensity stops working–which it always does–what are they left with? They can only add more water or acknowledge that they were wrong. Sadly, they’d rather add water to an already-crumbling castle.
When wet sand starts to lose its structural integrity, adding more water isn’t the solution. Drying it out is.
Likewise, when fitness starts to break down, it’s usually from too much intensity. Adding more intensity will make it worse, not better. The solution is to add more “dry sand”, more easy volume.
<Too-much-water-destroys-the-castle.png>
When sand is oversaturated, it starts to crumble. Adding more water is not the answer…
