I was thinking about sitting as I rode home tonight; trying to feel the difference between sitting "back" more on my sit bones and rotating my pelvis a bit more forward, resting more on the middle of my pelvis. It feels more secure--I rotate forward by my center of gravity is farther back, I'm bringing more of my back muscles into more natural alignment to support my torso, etc. But is is kind of something I need to work at as I ride--it's not totally automatic how I plant my butt on the saddle. There is some technique to it, that I learn. Like I've always had to learn muscle memory for things--riding a bike, playing piano, tap dancing.
It occurs to me that a way to gloss a lot of my thinking about bike fit, bike setup etc. is that I'm working at learning how to sit on the bicycle. For one thing, I think this glosses my ideal of how the bike should fit and feel--it should be something that your are sitting on securely, as a piano player might sit on their bench or a worksman sits on a stool. I'm not talking about a plush barcalounger or the heated massaging leather seats of a Mercedes S-Class, nor some kind of sinister exercise machine where you're forced into doing a pushup at the same time you're pedaling, but the secure seating of a person who is working at something.
The gloss "learning to sit on a bicycle" also connotes for me Buddhist meditation, and the attention paid in certain practices like zazen to learning how to just sit. Of course, some might take issue with my connection between bike fit and meditative practice, saying that bike fit is a process of trying to create comfort through material manipulation, while meditation has little to do with comfort (just ask those who do it for long periods) and everything with the spiritual, not material, practice of sitting. But go with me here for a while. Of course, meditation isn't "just sitting." A great deal of attention is paid to the (material) form of the sitting body, the arrangement of the legs and hands, the relaxation and extension of muscles and tendons, the posture of the torso, and running through this all, an attention and mindfulness of breathing. Meditation involves a great deal of mindfulness about the otherwise autonomic aspects of inhabiting a body.
I think the same things could be said to be true of bike fit. While it certainly results in making a bike more comfortable and avoiding pain, especially in the the arms and back, bicycling--especially spirited riding--accepts the effort and sometimes pain of using your body to propel yourself forward. If you can give up the notion that bike fit is about maximizing your potential and making yourself go faster, in my mind it becomes the pursuit of being able to be settled on the bike, achieve a type of spiritual stability, with, again, a focus on breath. Riding a bike up a hill is always going to be hard, but if you have found a good way to sit, all you need to do is focus on the rhythm of breathing and pedaling.
Of course, the physical practice of sitting in meditation involves little more than the body and maybe a small stool or pillow, so practicing sitting need not involve any material attachment or possessions, while learning how to sit on the bicycle involves not just the body but also changing the material dimensions of the bicycle, changing pedals, shoes, handlebars, or seats, and thus involves material and often financial investment. If you can get beyond the simplistic thought that one change, one new component or even a new bicycle will be the "answer," however, you start to see how bike fit can be about developing meaningful connections between the external and internal worlds. It requires a great deal of learning to listen to the body, mindfulness about how it is arranged, feeling how small changes of posture can affect the way that energy flows through the body.