The basics of TSS and IF
IF= Intensity factor, which is Normalized Power for the ride divided by your FTP
TSS= Training Stress Score uses IF and duration to give you an idea of how “hard” a session was.
Four-Dimensional Power and TSS/IF
With 4DP, the workouts are individually tailored based on your ability to produce power above FTP. For shorter harder efforts, the power targets can be drastically different even if those two riders have the same FTP.
For example, 2 riders both with an FTP of 200W. Rider 1 can hold 500W for 1 minute, Rider 2 can hold 350W for 1 minute.
Having both riders do 5 x 1-minute repeats at 150% of FTP (300W) would give identical IF/TSS values since their FTPs are the same.
However, Rider 1 will find this workout much easier than Rider 2.
Having the riders do 5 x 1-minute repeats at 90% of 1-minute power (450W and 315W respectively) will effectively make the session equally “hard” for both riders, though Rider 1 will have a much higher IF and TSS for this session
How this affects you...
The “Planned” values found in our app and in TrainingPeaks are based on the workout files that only use FTP, which does not necessarily match up with the power targets you were actually given in the video.
For some riders, you will regularly see IF values well above “planned” and for others, you will regularly see IF values well below “planned”. It's OK, don't worry. Keep calm and Suffer on.