I am using a Suunto watch to record activities. The data is analyzed in Suunto App which uses training metrics powered by Training Peaks, which is an established leader in this area. The same data is uploaded to Strava that provides its own training metrics. In both cases I can see Fitness / Fatigue / Form metrics that, as I understand, are supposed to be based on the roughy the same formulas. However the metrics look quite a bit different. Let’s do a comparison.
Here is the Training Peaks data from Suunto app for the last 8 weeks. You can see that the Fitness metric has been going mostly up from 43 on 1/6/25 to 56 on 3/2/25 - 30% increase. That seems reasonable to me as I’ve been ramping up the volume. The intensity remained roughly the same because I train for ultra distances. Note how smooth the fitness graph is overall, which is reasonable because the fitness level doesn’t really change that fast. Also note the clean representation of the Form metric, which is essential to targeting the training in the most productive zone from -10 to -30. Strava also has the Form metric, but only on the web, and it provides zero guidance.
Now let’s look at the Strava Fitness graph for the last 3 months. What we can see in comparison that Fitness graph is a lot more volatile - it goes down significantly more between my long runs where I tend to have the most training load. And overall it remained mostly flat in the same period - it changed from 63 on 1/6/25 to 67 on 3/2/25 - 6% increase. There is no trend that I can see despite the increase in the training volume. Also the Fatigue metric looks a lot more volatile than in the Training Peaks case.
So the question is why these two graphs are so different between Training Peaks and Strava? The former makes much more sense to me based on how I trained recently, but the latter makes very little sense. Can anyone from Strava comment on this?
