If you train with any kind of structure, you’ve probably had this moment:
“The numbers say this should feel easy… so why do I feel absolutely wrecked?”
“Am I actually getting fitter, or just better at tolerating discomfort?”
“How much should I trust my data… and how much should I trust my gut?”
Here’s the honest answer (from a coach who uses the data and listens to athletes):
Metrics tell part of the story. RPE tells you whether that story makes any sense.
Let’s break this down in a way that actually helps, whether you’re learning the language of training or you’re deep enough into TrainingPeaks that you’ve started emotionally identifying with your CTL.
1. Training Stress Score (TSS): The Currency of Training Load
TSS is TrainingPeaks’ attempt to turn “how hard was that?” into a single number by combining intensity + duration.
The rough benchmark:
~100 TSS ≈ 1 hour at threshold
That means:
Long, steady, “easy” rides can rack up real stress
Short, brutal sessions can do the same
That part is useful. But here’s where people get into trouble.
Coach reality check: Two workouts can have identical TSS and completely different consequences.
One leaves you pleasantly tired
The other leaves you questioning your life choices for three days
TSS tells you how much work you did. It does not tell you how well your body tolerated it. That’s not a flaw, it’s just a limitation. And it’s why context matters.
2. Normalized Power (NP) & Intensity Factor (IF): “How Hard Was It, Really?”
Normalized Power (NP) accounts for variability. Surges, climbs, accelerations – it “weights” hard efforts more heavily than easy ones.
Smooth ride → NP ≈ average power
Spiky ride → NP much higher than average power
This explains why two rides with the same average power can feel wildly different.
Intensity Factor (IF) tells you how hard the session was relative to your current fitness.
- IF = NP ÷ FTP
General ranges (very general):
0.60–0.70 → Easy endurance
0.80–0.90 → Tempo / threshold-adjacent
>1.00 → Hard, unsustainable, limited-repeat stuff
NP and IF help explain why a session produced a certain TSS.
But they’re only as good as the assumptions underneath them. FTP is estimated, zones drift, physiology changes – the model is never perfect.
3. CTL, ATL, and TSB: Fitness, Fatigue, and Timing
Once TSS stacks up over time, TrainingPeaks starts modeling what it thinks is happening to you.
Chronic Training Load (CTL) – “Fitness”
~42-day rolling average of TSS
Represents the workload you’ve proven you can sustain
Rising CTL → expanding capacity
Flat or falling CTL → consolidation, recovery, or life happening
Acute Training Load (ATL) – “Fatigue”
~7-day average of recent stress
How beat up you are right now
Training Stress Balance (TSB) – “Form”
TSB = CTL − ATL
Negative TSB → carrying fatigue, building fitness
Positive TSB → fresher, sharper, closer to race-ready
These tools are incredibly useful when they reflect reality.
4. RPE: The Metric That Keeps the Others Honest
RPE (Rate of Perceived Exertion) is your subjective rating of how hard a session felt, usually on a 1–10 scale.
RPE captures everything your devices can’t:
Sleep quality (or lack of it)
Heat stress
Work stress
Travel
Under-fueling
Low-grade illness
Mental fatigue
Your power meter has no idea you slept four hours and skipped lunch, but your nervous system absolutely does!
Where RPE becomes invaluable...
This is what coaches look for all the time:
Easy endurance ride
Low IF, low TSS
RPE = 7/10 (red flag!)
Threshold workout
Expected RPE ~8/10
RPE = 6/10 (adaptation happening)
When RPE and the metrics consistently drift apart, something’s off:
Zones may be wrong
Fatigue is accumulating
Fitness has changed faster than the model
Ignoring that is how people end up “following the plan” straight into burnout.
5. How Coaches Actually Use Metrics + RPE Together
For newer athletes:
Learn what easy, moderate, and hard actually feel like
Use RPE to sanity-check zones
Don’t chase numbers at the expense of consistency
If “Zone 2” feels like a race, it’s not Zone 2... no matter what your watch says.
For experienced athletes:
Use RPE to interpret CTL ramps and fatigue trends
Spot early signs of overreaching before performance drops
Adjust when life, heat, or travel changes the cost of training
Coach rule of thumb:
When metrics and RPE agree, confidence goes up. When they disagree, RPE gets the final vote.
6. Big Picture: Metrics Are Maps, Not the Terrain
TSS, NP, IF, CTL, ATL, and TSB are powerful tools, but they’re still models.
RPE is how you:
Catch problems early
Individualize training
Avoid chasing perfect charts into the ground
The best performances don’t come from blindly obeying numbers. They come from using data to support good decisions, but not fully replace them.
Final Coach Takeaway
If you only track numbers, you miss context. If you only track feelings, you miss patterns. The magic is using both – honestly!
– Coach AJ Sobrilsky, Endurance Coach and Doctor of Physical Therapy