Athlete Assets · Article
TSS vs NTS: understanding training stress
Explore the differences between training-load models and use their scores in conversation with your coach.
By Precision Coaching
Training stress scores aim to turn a complex session into information that can help you and your coach plan what comes next. Our downloadable guide introduces FitLogic’s Normalized Training Stress (NTS) and compares it with Training Stress Score (TSS).
The useful starting point is to understand the model behind each number. Different scales are not interchangeable, and a larger score is not automatically a more accurate measurement of what your body experienced.
How TSS represents a session
Power-based TSS combines duration with intensity relative to functional threshold power. It uses Normalized Power rather than simply average power. For this version of TSS, the relationship can be expressed as duration in hours × Intensity Factor squared × 100.
That is an important clarification to the downloadable sheet’s wording: power-based TSS is not a simple linear calculation of average intensity. TrainingPeaks explains Normalized Power, Intensity Factor and TSS here ↗.
What NTS is designed to add
FitLogic describes NTS as accounting for intensity, session composition, environment and different types of stress. Its approach separates aerobic, threshold, muscular and neural demands, with the aim of informing individual load management and recovery planning. Read FitLogic’s explanation of NTS ↗.
Three questions to ask about a stress score
How is intensity weighted?
The supplied comparison focuses on how harder efforts are represented. Check which metric was used and whether your threshold or assessment settings are current before interpreting the result.
What happened within the session?
A steady ride and an interval session can have similar overall scores while asking different things of you. Look at the work and recovery intervals alongside the headline number.
How does the session fit your week?
Your recent training, availability, environment and feedback all matter. Tell your coach when your experience differs from what the activity file appears to show.
The guide’s 15-minute example
These are the illustrative values reproduced from the supplied guide and FitLogic’s comparison. They describe those models’ scores, not a direct measurement of physiological stress or a universal conversion between systems.
| Effort | TSS | NTS |
|---|---|---|
| Zone 2 | 12 | 7 |
| Zone 4 | 25 | 23 |
| Zone 5 | 33 | 72 |
| Zone 6 | 39 | 151 |
Use the numbers to support decisions
Follow trends consistently, keep your data accurate and discuss unusual results with your coach. No single score captures every aspect of recovery, readiness or life stress. The goal is a better-informed next session, rather than chasing a particular total.
You can also read Why do training platforms give different stress scores? in the Training Library.