Very short (15–20s) Smart Intervals for VO₂ work with high HIE — how should this be interpreted?

Training
1

Hi all,

I’ve been using Xert for a while and really appreciate the model and the concept of strain-based training. However, I’m struggling to understand how to properly use Magic Buckets together with the Smart Interval recommendations for high-intensity (VO₂-type) work.

My fitness signature

  • TP: 361 W

  • HIE: 24.7 kJ

  • Peak Power: 1182 W

So I appear to have relatively high anaerobic capacity.

The issue

When riding with Magic Buckets and following the real-time interval recommendations on my head unit, I consistently get suggestions like:

“30 intervals @ 546 W for 17 seconds”

In practice, most of my suggested “intervals” are:

  • 15–20 seconds

  • sometimes even shorter

  • almost never longer (e.g. 60–90+ seconds)

What’s happening (as I understand it)

It seems that:

  • I can generate very high power

  • HIE depletes quickly

  • MPA drops fast

  • strain accumulates very quickly

So the system reaches the intended training load almost immediately.

My concern

From a physiological standpoint, these efforts feel like:

  • repeated short anaerobic bursts

…rather than anything resembling sustained VO₂max work.

Coming from a more traditional background, VO₂max training usually involves:

  • longer efforts (2–5+ minutes)

  • sustained high oxygen uptake

  • accumulating meaningful time at intensity

With the current recommendations:

  • I reach high strain very quickly

  • but spend almost no time at that intensity

Key question

For athletes with relatively high HIE:

:backhand_index_pointing_right: Is Xert effectively allowing us to “overuse” anaerobic contribution to hit strain targets?

:backhand_index_pointing_right: And if so, could this lead to insufficient time at VO₂max, despite technically hitting the intended training load?

Buckets vs execution

I understand that:

  • Buckets accumulate over the entire ride

  • They are not tied to individual intervals

So the real issue is not the bucket concept itself, but rather:

:backhand_index_pointing_right: how the recommended efforts are executed and metabolically achieved

Right now, it seems very easy to:

  • fill high-intensity buckets via short spikes

  • rather than sustained work

What I’ve tried

I’ve experimented with:

  • Ignoring the short interval recommendations

  • Riding longer, steadier efforts closer to MPA

  • Adding more traditional VO₂ intervals

This feels much more effective physiologically — but also like I’m deviating from Xert’s intended use.

What I’m trying to understand

  1. Are these very short interval recommendations expected for high-HIE athletes?

  2. Should these be interpreted more as “intensity signals” rather than literal interval prescriptions?

  3. Does Xert assume that proximity to MPA is sufficient regardless of duration?

  4. Are there recommended ways to avoid ultra-short, spike-driven bucket accumulation?

Final thought

I really like the Xert model, but in this case I’m struggling to reconcile:

  • very short (15–20s) recommended efforts
    vs

  • the need for sustained high-intensity work

Especially for VO₂max development.

Would be very interested to hear how others with similar profiles approach this.

Thanks!

1 Like
2

I am also a bit confused by that. Most MB workouts seem like a Z2 ride with many very short “needle” intervals. When you create a MB workout in the generator, I think you can determine the interval duration. But I am not sure it transfers in any way to “dynamic” outside MB rides.

1 Like
3

This behavior of the algorhithm reminds me of this old story - when the military started using the first computers, they asked what would be the cheapest way to feed a soldier, in a way that provides all the necessary nutrients. The computer calculated that each soldier should just eat 25kg of potatoes every day. Similarly, Xert says you shold just do 100 short, 15s bursts during your workout.

2 Likes
4

I think I read somewhere in the Knowledge Base that MB calculates “the most efficient” way to fill the 3 XSS buckets for the day. My hunch is that it does not necessarily take into account the traditional idea of what a VO2Max interval should look like. I don’t have enough knowledge or experience to critisize the Xert approach, but I do wonder how grounded it is in actual sport science. I’m afraid we might be just getting “25kg of potatoes”.

1 Like
5

I really love Magic Buckets, it makes training fun. But unfortunately, I have to ignore its recommendations. It suggests a 30-second recovery, then a 2–3 minute one . From a training efficiency standpoint, recovery is one of the most critical factors, so you need to clearly understand what exactly you are training and how

2 Likes
6

So you use MB basically to monitor your XSS across the buckets rather than an interval guide, correct?

7

There was a very interesting discussion on the Xert podcast, where Armando and Scott from Xert had a kind of disagreement with their guest coach Steve Neal:

Listen to the bit from 36:10 to 44:00. It’s not exactly the same problem you are describing, but it does seem to highlight the difference in thinking about training stimulus between Xert team and a more mainstream-minded coach.

8

I found this topic, where the issue of microintervals was discussed:

My takeaway is that it is up to me to decide if MB microintervals is something that will be beneficial for my training, because the algorithm seems to care more about time-efficiency and filling the buckets than about giving me the best workout in a traditional sense. Which is a pity for me because I don’t know anything about training and was hoping Xert would do all the thinking for me.

9

Same here. My TP is similar to yours but my hie is considerably smaller 14.7 kj and my pp also lower 945w. So I don’t think that those short intervals recommended by XMB is for anaerobically gifted athletes since it happens also in my diesel case