Your head unit already knows it. Most riders never look. It's called TSS, and it is the single number coaching science is built on.
TSS, Fitness, Fatigue and Form. The four numbers that make a coach's decision possible, and why going into the red is the point.
TSS measures the dose, not the absorption. HRV, resting heart rate and sleep are how the body reports back, and why a raw number means nothing.
Recovery to sprint: what each system runs on, how long it takes to build, and why your body doesn't care whether the stimulus came from a trainer or a 14% ramp.
Relative Load: every ride is a dose, and FORM sizes it against your own Fitness. Why the ride that flattened you in March is a normal Tuesday by July.
Feeling isn't fact. Training Impact tells you what a ride actually hit and how hard, so you know instead of guess.
Polarization. Most of your hours easy, a few of them very hard, almost none in between, and the research FORM's coaching is built on.
Base, Build, Peak, Recover. Periodization is how load becomes fitness instead of fatigue, and why week 3 is always the hard one.
Compliance is not obedience. It's the gap between the session you planned and the dose you got, and what the coach does about it.
Grams per hour, not grams per ride. How fueling scales with intensity, why the long ride bonks at hour three, and what a plan looks like.
Course Coach turns a GPX file into a pacing plan: where to spend, where to save, and what your finish time actually depends on.