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5 July 2022

Estimating NP®, IF®, TSS®,

by Stuart Lynne


FTP, NP®, IF®, TSS®, were introduced by Hunter Allen and Andrew Coggan, PhD in their book Training and Racing With a Power Meter


FTP or Functional Threshold Power is the power that can be maintained for roughly one hour.


NP® or Normalized Power ® adjusts the power data of a workout to account for the increased stress of the intensity. From the book:

  1. Starting at the beginning of the data and calculating a 30-second rolling average for power,

  2. Raising the values obtained in step 1 to the fourth power;

  3. Taking the average of all the values obtained in step 2; and

  4. Taking the fourth Root of the number obtained in step 3.


IF® or Intensity® of a workout is defined as:

    intensity = np / ftp


TSS® or Training Stress Score ® was developed by Dr. Andy Coggan to represent the physiological impact of a workout that takes into account the intensity of the workout.

TSS is defined as:

    tss = (duration of workout * NP * IF) / (FTP * 3600) * 100

Differences between implementations

The implementations of Normalized Power vary because the it is based on the data collected from power meters which is then transmitted via either Ant+ or BLE to the collector of the data. This process is not lossless. Data can be lost.

How the missing data is corrected or interpolated is not specified.

From a (SlowTwitch forum post) (,_IF,_NP,_etc.__P3910865) , May 7, 2012:

May 7, 12 10:27
Post #23 of 30 (6722 views)
We are happy to discuss the use of the terms with anyone, we claim no royalty, simply attribution. 
The formula for TSS based on power is public knowledge, but it is held as trade secret 
on how we handle data-gaps and other specific circumstances when applying the formula. 
CEO, Peaksware

See also

Analyzing your Cycling Data Johannes Jacob Build Your Own Performance Chart Johannes Jacob

[Training Stress Score for Cycling: What TSS is, how to use it, and what it doesn’t tell you] (

Estimating Training Stress Score (TSS®) JOE FRIEL


The names of some TSS® statistics are registered trademarks of TrainingPeaks.

See: [TrainingPeaks About Us] (

Our Trademarks

By introducing scientific tools and methods that have become the industry standard, TrainingPeaks has revolutionized the way that coaches and athletes track, analyze and plan endurance training. Our registered trademarks include TrainingPeaks®, TSS®, Training Stress Score®, IF®, Intensity Factor®, NP®, Normalized Power® and VirtualCoach®.