Bike Fitting:
Bike fitting is about biodiversity. Every person is different. Different skeleton, different muscle development, different injury history, different skill sets. Bike fitting is adapting a well understood machine (the bike) to a machine which is different in a zillion ways from the last fitting (the human body). The bike fitter's job is to understand the relationship between bike and body. The bike fitter's best resource is experience.
After 30 years of bike fitting, I'm starting to get it...
My bike fittings have 3 basic goals.
1) put the rider within range of motion in every direction.
Range of motion: Every joint on the body has a limited range of motion. If that joint is within range of motion while exerting force it's called exercise. If the bike is taking that joint beyond it's range of motion it's called injury. Most people are willing to ignore being outside range of motion because single cycle only produces a small amount of force. Multiply that small force by the number of times the pedals go around and you begin to see the real picture... Within the pedal stroke there are two points which challenge range of motion, the 12:00 position (greatest angle at the hip) and 5:00 position (greatest distance from hip to pedal). Both of thses points in the pedal stroke must be within range of motion while the rider is in their riding position.
2) get the rider's body weight on the pedals.
This is where my fittings diverge from the rest of the fitting world. Most fitters stick to adjusting the bike, assuming the rider has the right skill sets. I've observed far too many cyclists riding around with 1/3rd of their body weight on the handlebars to believe that. People learn how to walk on solid ground which they trust to hold up their body weight. Get on the bike, put your feet on the pedals and there is no more solid ground, the pedals move. Your brain goes into panic mode and finds the next solid object to support your weight - the handlebars. Weight on the pedal going down is power, weight supported at the handlebar is just causing problems. I teach my clients how to get their full body weight onto the pedals. I don't understand how a fitting can work without that step.
3) deal with injury and/or asymmetry.
I can't begin to explain this. I've been a bike fitter for 30 years, being the coach of the Harvard cycling team gave me access to their teaching hospitals, so I have the resources. That said, every human body is a complex puzzle.
Critical thinking in bike fitting:
When I started as a bike fitter at Wheelworks I was shown how our system (FitKit) worked, how take measurments and how to adjust the bike based on the charts. I did my first fitting on a friend, then did what no fitting school suggests - I went for a ride with my client. Had I never seen someone I fit riding, I could assume it all works. It doesn't (and they'll never tell you that). How well a fit works is a function of the rider's skill sets.
In general, bike fitters don't ride with their clients. The reason they give is that they would never have the time. I can think of two real reasons:
1) they haven't made their own bike fit work.
Bike fitters have no excuse here. Each bike fitter is issued one human body on which they can test anything or everything fitrelated - their own body. If they can't get their own fit right, don't go to them for your fit. This has nothing to do with fitness, we're talking bike fit.
2) seeing the actual results makes the job much harder.
My entry into bike fitting was assisting John Allis in coaching the Harvard cycling team. Each September we would get new riders who we had to fit on their bikes. Creating a race team means dealing with all the problems - their fits had to work. What I learned was that a rider on a trainer in the fit studio isn't the whole story, and that bike fit isn't static. Human bodies change and adapt.