But what about outdoor training?
As you can see this has already come up twice which is partially my fault for accidentally omitting the word 'indoor' from my title.
Incidentally, however, many of these concepts can also apply to the outdoors albeit over a long enough time such that variation comes out in the wash. What this means is that improvements and changes to other metrics will need to be more pronounced and consistent before they are detected. For example, when rides around your neighborhood become laps around your neighborhood or average speed for the same effort becomes consistently faster then you are improving. This is the natural and intuitive application of the internal to external ratio we all do even if we don't know what it's called.
I'm not an advocate for indoor training. I just choose to do it because it suits my personality and also I don't want to die from being hit by someone who is texting.