Originally Posted by
redlude97
Strava "fitness" or elevate "fitness" is not real fitness, so it doesn't matter what the numbers say. TSS and relative effort are just training metrics. Measure fitness in terms of increases in FTP or times on a repeatable segment of road. There are lots of ways to create the same TSS/RE but not all add to your performance capability in the same way.
The tricky part of your assertion, which is quite correct IMO, is that measures of fitness depend on what you're trying to do. FTP or segment times might not be perfect metrics either. Maybe one needs to watch one's times on a 40k TT or maybe on a 60 mile road course or performance in a pack sprint. IME if one's training mimics one's goal rides, watching CTL does seem to work in that too high is unsustainable, too low = poor performance. Whether one can modify one's training within the same CTL parameters to produce higher performance in one's goal rides I think is your point and a good one. IME that requires experimentation and expert advice. I keep fooling with that but haven't come up with anything firm other than "ride hard, make your legs and lungs hurt, then recover less than you'd think."