FORM=FITNESS + FRESHNESS
What is form? A lot of cyclists don't know what it is but they know what it feels like to be in "form". And coaches know that's what they want their athletes to be on race day- maximum form. By definition, Form=Fitness + Freshness. And, we all know what fitness is, or being fit. But what about Freshness? Being Fresh is the opposite of being Fatigued. Thus, the Form equation could equally have been written: Form= Fitness - Fatigue.
I'll better define Form=Fitness + Freshness via an example. Ex. At the end of the Tour de France a rider can be very Fit but very Fatigued, therefore the rider will not be in Form (he'll have a low Form value). In some cases, the Fatigue value can be higher than the Fitness value and the Form value will be negative (which is not good). On the other hand, that same Tour de France rider can sit/rest for 2 months after the Tour and be very Fresh but have lost Fitness resulting in a low Form value.
How do we get Fit? We get Fit by stressing our body. Our body reacts by making it stronger so it can handle the stress better the next time it's stressed. Freshness is the result of rest.
Lets take a look at a Form chart (provided by Strava) over the last 6 mos. of my riding (see below):
According to Strava, my current Fitness level is 18 (unitless value). You can see it's as high as it's ever been. However, I've had two hard rides in the last 5 days and my Fatigue level is 34 (also unitless). Therefore, if you do the math, my Form=18 - 34= -16. That's not very good to be in the negative for Form. i.e. it's not a good time for me to be looking to break any personal records on the bike with respect to power and/or speed. The legs just won't have the endurance and/or power until I rest a bit. So, what is the magic number for Form? I don't think there really is one. It differs for everyone. Some riders like to be really Fresh (not having ridden in a couple days) while others need to have ridden a day or two before the big event. But, you definitely want a positive value for Form. When you have a good/strong day on the bike, whether it's a race or recreational ride, take a look at your Form number from Strava. I believe you need to log at least 15 rides in a 42 day period for Strava to generate an accurate Form number since it uses a weighted-average formula.