I'm an avid runner and like so many other runners, I like to get a measurement or number for my current fitness. I use the measurements for two purposes: to see how the different types of exercises affects the fitness and to see how much I can challenge myself for a specific race.
But how exactly can I measure fitness?
For the last 4 years, I have used SportTracks and in particular the Training Load plugin to calculate CTL, ATL and Training Stress Balance and have used these numbers as a measurement for my current fitness.
Historically, these numbers comes from work by Dr. Coggan and others (as described in this article by Hunter Allen) for use by cyclists and was later adapted for use by runners. Originally, CTL and ATL was based on a power meter (TSS - Training Stress Score), but for runners the concept of TRIMP (TRaining IMPulse) was used instead as it is rather difficult to directly measure the power used by a runner. As TRIMP is based on a simple accumulation of your heart-rate over the course of the run, it makes good sense as an alternative to TSS.
But... I curious, and I wonder whether there are other similar (well-founded) numbers that can be used to calculate your fitness?
I forgot: One such number is rTSS (running TSS) by Dr. Steve Macgregor, but it seems to be nearly impossibly to use for your daily runs as it requires many subjective numbers...