Wish I’d written this better: Comment of the week: A brief intro to bike fitting
Bicycles have substantial bilateral symmetry. Humans, not so much; we just look that way.
That mismatch makes little difference for a casual ride if you feel comfortable. If you feel uncomfortable, or seek endurance or power, small changes in the fit between you and the bicycle can make a big difference given time.
Well fit, a bicycle like a good pair of shoes, you don’t notice and go all day. Poorly fit, you notice — sooner or later.
If the fitter doesn’t squat down and watch you from all angles, go somewhere else.
Fitting has gone through three major approaches.
The fitter makes bio-geometric measurements of the rider’s limb and torso lengths and adjusts the bicycle based on those measurements and formulas or tables. A goniometer improves the approach by measuring the angles of the rider’s limbs and torso while seated on the bicycle.
The fitter uses video motion capture to measure the positions and angles of the rider’s limbs and torso while the rider pedals a bicycle on a stationary trainer. This approach comes with a lot of technology and theater and has become a profit center for some bicycle businesses.
The rider warms-up on a bike on a stationary trainer. The fitter starts by assessing the rider’s range of motion off the bike, especially noting asymmetries of flexibility and strength. The fitter observes the rider pedaling the bike on the stationary trainer at a moderate pace and also during brief periods of intense effort. The fitter looks for many things, among those observing the acceleration of the knee at the bottom of the pedal stroke, which can indicate over extension.
This approach can help less pliable riders maintain or attain fitness or performance.
Just like an exercise to balance your strength or improve your flexibility, a change to the fit of your bicycle will not immediately change how you ride. You adapted to how the bicycle was. You need time to adapt to how the bicycle has changed. So initial fittings usually need follow-up.
Good fitting starts at the feet. The fitter looks for turnout, pronation, supination, varus, and valgus. For a rider that uses cleated shoes, the fit must confirm or correct the cleat positions. Cleats can lead to a lot of fit problems.
The bio-mechanical and neuromuscular approaches can start from the same place: assessment of the rider and asking the right questions; and have the same goals. But differ in what they look for at the end. The bio-mechanical approach looks at position, even if measured while moving. It has the possibility of some repeatability and quantifiable data, thus use for research, though it has no concern for proprioception. It works well for riders that fit the data, or who can afford extensive data collection, such as Olympians and well funded athletes.
A point of difference for example: measurement by goniometer or video looks for an angle of 150° ± 5° between the upper leg and lower leg at the bottom of the pedal stroke. Not a bad rule of thumb: it works for a lot of riders. But not if the rider has sufficient inflexibility, injury, or asymmetry of strength or flexibility. A practiced bio-mechanical fitter will spot when 150° obviously doesn’t work, but then with what judge the adjustment. And will they spot less obvious situations? Seeing with the machine can limit vision.
The neuromuscular approach looks at fine details and patterns of motion to see the results of how the rider gets from neural impulse to action. I cannot see the rider’s brain, tendons, or ligaments, but I can closely observe the results, knowing to look for specific telling details.
I clearly favor a neuromuscular approach to fitting. And have my own quirks: I want the rider to keep pedaling at all times while on the bicycle during the fitting — so I can continue to absorb watching them. I can explain fitting in terms of anatomy, bio-mechanics, neuromuscular responses, and find Steve Hogg’s concern with proprioception convincing. But I cannot fully explain how I see it. It has accumulated over years. The mind learns to see patterns, I notice, then I know to look more closely at something.
We do want something measurable so we can learn from fit to fit, from rider to rider: learn what works and become better. But a too mechanistic approach misleads. Us mostly bags of water, even the most lean and muscled, fit bikes rather sloppily. Attempting to work the material beyond its precision just annoys the material. And leads to false impressions because the material, beyond its precision, responds unpredictably. Mentalities of control and precision benefit when I adjust gears but not when I adjust for people. Sports medicine has learnt much in the last forty years, but my usual bicycle working tolerance of half a millimeter has no meaning in fitting. The finest precision with which I can adjust saddle height today will vary with tomorrow’s stiffness.
Any fitting that fails to acknowledge the imprecision of the process misleads, starting with the fitter. Any question of mechanical correctness I can eventually resolve with mechanical and materials engineering (and dismiss a lot of nonsense; Sharp, Barnett, and Heine have much use in this). But I need take great care in how I think about fitting or I could easily mislead myself into pseudoscience.
I cannot readily separate what I do from what I have learnt from a neuromuscular approach, so take care to not use what I do to describe a general neuromuscular approach.
(Steve Hogg has a different categorization and goes into detail: Perspectives on Fitting.)