TL;DR answer: All the way up and down. 
With a little help from AI (I asked a few more questions) –
The Xert model absolutely addresses different training stimuli — it just expresses them mathematically instead of through traditional zone‑based plans. In addition, Xert is adaptive from day to day.
Starting with MPA and XSS (not simple TSS) Xert’s multi-dimensional strain model combines Focus Duration, Specificity, and Difficulty with Progressive Overload. All of which is calibrated against your evolving three‑parameter fitness signature.
Focus Duration determines which physiological system is being targeted.
- Long focus → endurance/LTP
- Mid focus → threshold
- Short focus → VO2max
- Very short focus → anaerobic/neuromuscular
Two workouts with the same XSS total can have:
- Very different Low/High/Peak distributions
- Very different Focus Durations
- Very different physiological outcomes
Two workouts with same Focus but different Specificity will vary in L/H/P distribution and training effect. E.g. a Pure Rouleur (6 min power) workout requires a higher high/peak load resulting in a longer recovery requirement. Whereas a Polar Rouleur workout can have you back to blue/fresh well before the next day. Why? Because L/H/P recovery load differs. Your physiological response isn’t the same. Xert models that through L/H/P strain analysis.
Difficulty Rating (Easy, Moderate, Difficult, Tough, Hard) encompasses:
- interval length
- recovery duration
- intensity
- accumulated fatigue
- how close you ride to MPA
- how much strain is compressed into time
This is directly related to interval structure ranging from 30/15s, VO₂max time‑in‑zone, SMART intervals scaled to your signature (not anchored on %FTP), plus the default micro-interval sets in XMB.
Lastly, there’s Progressive Overload.
As training load increases:
- Xert automatically recommends harder workouts
- Focus shifts as needed (XFAI and XATA Base-Build-Peak; or DIY on Continuous)
- Difficulty increases
- Strain distribution changes
- Endurance vs intensity balance evolves
All of this occurs without rigid calendar templates, explicit workout progressions, or fixed training blocks.
Xert’s progression is indeed physiology‑driven, but not template‑driven like old-school training plans.
As I like to say Xert provides you with “The Freedom to Ride!”
As noted in my post here, XMB does not limit you to short intervals exclusively. You’re in control and variability is built into the tool.
If you’re time-crunched and sweet spot has worked well for you in the past, go ahead and include some on LIT days.
Yes, self-coaching factors in. As much or as little as you like.
Prefer more structure with a pre-populated calendar to gaze at? Go XFAI.
Open to following a phased progression running in background with ability to choose day-by-day? Go XATA Base-Build-Peak.
Want the most amount of DIY freedom? Go XATA Continuous.
Check out my program comparison chart here.