Training Knowledge · Article
Why do training platforms give different stress scores?
Understand what NTS and TSS are trying to describe, and why comparing their numbers directly can mislead you.
By Precision Coaching
You finish a hard session, upload it to two platforms and receive two very different scores. Which one is right? The first step is to check what each score represents.
Different models use different inputs and scales. A bigger number is not, by itself, evidence of a more accurate measurement. Nor does it establish that your body experienced a particular multiple of stress.
Understand the model
TrainingPeaks describes Training Stress Score (TSS) as an estimate that combines duration and intensity.
FitLogic describes Normalized Training Stress (NTS) as incorporating session composition, discipline, environment and an individual training stress profile. That is its stated approach to modelling a workout's demands. The description alone does not establish that one platform produces better outcomes for every athlete. FitLogic's NTS explanation ↗.
A useful comparison starts with the session
In our original post, a hard 5 km effort followed by easy running produced different scores in two platforms. That is a useful prompt to investigate how each system treats the workout. It is not a controlled test proving that either number measures the exact physiological cost.
Before drawing conclusions, check:
- Which metric was calculated: power, pace or heart-rate based?
- Are your threshold settings current?
- Is the activity file complete, with plausible sensor readings?
- Does the score make sense alongside the actual intervals and your feedback?
Use scores to ask better questions
Follow trends within a consistent system and understand its limitations. A score can support a discussion about the next session; it cannot guarantee recovery, predict an individual injury or replace how you feel. Tell your coach when the number and your experience seem to disagree.