Why do Mixed-interval Threshold workouts have such high IF compared to other Threshold types

TrainerRoad Software
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I’m about to start the Gran Fondo Specialty phase, where my Threshold workouts go from 90 minutes down to 60 minutes. At the same time, the workout style shifts from mostly over-unders and classic intervals to mixed-interval Threshold sessions.

Looking ahead at these workouts, they seem much tougher, and I’m not sure I’ll be able to complete them comfortably, even though my recent Threshold sessions have all gone well.

For context:
FTP 294 W
My strengths are in the 1–5 minute power range, so VO2 work usually feels manageable
My VO2max progression level is generally higher than Threshold
I usually rate Threshold workouts as hard or very hard, but I’ve been completing them consistently

What stands out is that many 60-minute mixed-interval Threshold workouts have a noticeably higher IF than other Threshold types at the same progression level.

A few examples:
Teutonia (PL 4.0) – IF 0.92 – 3 sets of 1–4 min at 100–115% FTP with 30 s rest
Santiago (PL 4.5) – IF 0.94 – 3–4 min at 101–105% FTP with 30 s rest
Ochiltree (PL 4.9) – IF 0.95 – 1–5 min at 99–115% FTP with 30 s rest
Hassler (PL 5.3) – IF 0.96 – 1–5 min at 96–113% FTP with 15 s rest
Talia (PL 5.5) – IF 0.97 – 3–4.5 min at 103–105% FTP with 15–30 s rest

By comparison, other Threshold workouts at a similar PL are usually around IF 0.86–0.92, like Lamarck, Darwin, Mary Austin -3, Spickard, Stevens or Washington.

The mixed-interval workouts seem to pack a lot more stress for the same PL, and the short recoveries make them look quite demanding even before trying them.

I’d be interested to understand why these mixed-interval Threshold workouts show such high IF values compared to other Threshold formats at the same PL.

And for Gran Fondo preparation, would it make sense to progress mixed-interval Threshold separately from the more traditional Threshold workouts to avoid unrealistic jumps?

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I can’t answer your question, but what I can say is that these workouts routinely destroy me and I rarely finish them. Usually this results in me doing workouts that are at least 2 levels below my threshold performance level. At that point I can finish them but it’s still painful. I always dread this part of the season. That’s just my experience. Maybe it will go better for you. Good luck!

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Normalized Power is higher, therefore IF is higher.

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Thanks, but my point wasn’t really about IF or NP themselves. I just used IF to show how much harder these mixed-interval Threshold workouts feel compared to other Threshold types at the same progression level.

A good example is Mary Austin -3 and Ochiltree, which are both PL 4.9 in the Threshold zone.

Mary Austin -3 has two sets of 2x10-minute over-under intervals that gradually step from 95% to 100% to 105% FTP and then back down again. There’s one minute of rest between intervals and five minutes between sets. It’s a tough workout, but the short valleys and decent recovery make it manageable.

Ochiltree, on the other hand, has three sets of 1–5 minute efforts between 99% and 115% FTP with only 30 seconds of recovery between intervals and about 90 seconds between sets. There’s hardly any time to reset, and the intensity stays around threshold or higher for almost the whole hour.

Both workouts have the same progression level, but Ochiltree has an IF of about 0.95 compared to 0.91 for Mary Austin -3, and the difference in overall difficulty is huge. That’s really what I was trying to understand: why two workouts at the same level can feel so far apart, and why the mixed-interval Thresholds seem to load so much more fatigue than anything else in the category.

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Ok, I misunderstood, but NP is trying to quantify the physiological cost so from that standpoint it makes sense that the workout with higher NP would feel harder.

For me this is like comparing climbing a steady grade versus a surgy climb. Each of those power surges come at an anergy cost, especially those touching VO2max power levels. There’s also the mental aspect of settling in for consistent effort that makes them feel easier mentally than varying efforts. As for the equal PLs, only TrainerRoad can answer that.

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I agree that the mixed Threshold intervals seem like the Workout Level rating is way too low

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I’d agree that those workouts do seem to be scored low PL wise.

But TrainerRoad wouldn’t prescribe them if the system didn’t think you could do them.

I’m assuming you have adaptive training turned on? I wouldn’t be surprised if those future workouts get toned down nearer the time.

For instance I have noticed that my next 1 hour mixed interval threshold workout is Ochiltree which is a level 4.9 even though my current threshold level is 5.5.

Just going off levels I’d say it should be too easy but looking at it I can see that it will be challenging but doable - so the right workout.

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I think whatever rules govern the PL scoring goes a bit wacky with those really short rests between intervals.

If you compare Ochiltree with Manzanita for example they are pretty much the same workout but Manzanita is scored far higher just because those short rest intervals are at a higher power - but they are so short it doesn’t really matter. :man_shrugging:t2:

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Yeah, it would be nice if TrainerRoad adjusted how these are scored. Even if Adaptive Training gives me lower-PL workouts when needed, the whole system still has that game-like effect where you naturally want to see your levels go up. I’m sure I’m not the only one who sometimes picks a workout just to raise the PL, so it’d be good if these mixed-interval sessions were rated a bit more in line with how hard they actually feel.

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I’m also definately guilty of declining an adaption if its to a lower level workout :sweat_smile:

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