Understanding Training Stress Score (TSS)

TSS is a composite number that takes into account the duration and intensity of a workout to estimate the overall training load and physiological stress created by that session. It was developed by Dr. Andy Coggan and Hunter Allen.

The Formula

TSS = (sec x NP x IF) / (FTP x 3600) x 100

Where:

sec: Duration of the workout in seconds
NP: Normalized Power (estimate of the physiological cost if the ride had been perfectly steady)
IF: Intensity Factor (NP / FTP)
FTP: Functional Threshold Power

Typical TSS Values

< 150 (Low): Recovery generally complete by the following day.
150 - 300 (Medium): Residual fatigue may be present the next day, but gone by the 2nd day.
300 - 450 (High): Some residual fatigue may be present even after 2 days.
> 450 (Very High): Residual fatigue lasting several days likely.