Originally Posted by
gregf83
I believe Strava let's you select whether you feed Power and/or HR data into the Fitness/Freshness calculations. If you select power only I think the Strava Fitness/Freshness is the same as Dr Andrew Coggan's CTL/TSB/TSS data.
It's similar, but not exactly the same. Strava uses a different formula for Weights Power (Normalized Power in Training Peaks terminology). Above-threshold efforts are more heavily weighted in the TrainingPeaks/Coggan formula than in the Strava formula. Since normalized power is used to calculate TSS and all the other metrics, that means the Strava numbers will be a little different, especially if you're doing lots of high-intensity stuff.
The other big limitation with Strava is historical data. In Strava everything is based on your current FTP setting. So if your FTP is changing, the historical data becomes inaccurate.