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Tuesday, June 12, 2012

Rules of Bike Fitting

This is by no means a comprehensive list, and I'm sure that it'll keep growing and morphing but here you go:

1.  You must use Reason  --  Reason is King.  If you don't have a solid basis for why you're doing something, then you shouldn't be doing it.  I do a lot of fittings for people that have already had a bike fit and are still having difficulties on the bike.  So many of these failed fittings are the result of the fitter making changes to their fit without any real reasoning behind them.  Often they fit a certain way because "that's how we've always done it."  That's not good enough.

2.  Always consider the "whole" while looking at the parts -- Regional Interdependence is the idea that parts of the body (even distant ones) are inextricably linked, and affect one another.  This is a very common theme drilled into every PT student, and one that is especially important when on the bike.  The bike is one of the few tasks where we move with and against a device that we attach to at 5 different points (you can make the argument for 6 contact points if you consider each sit bone, and therefore each side of the pelvis to be separate entities) and when we make a change at one of these points it has the ability to create changes everywhere else.  This is why good bike fitting is so difficult -- a change in foot position is very likely to cause changes even at the rider's shoulder and neck -- reading and trying to predict these outcomes comes only from a deep knowledge base.

3.  A bike fitter needs lots of academic training AND lots of practice -- To successfully combine #1 (Reason) and #2 (Regional Interdependence) requires a lot of education and training, and it's important to realize that these are two different things.  Education is learning all the basics about the bike and the human body (and the human body information is significantly greater in scope) while training is the act of applying this knowledge.

The best scenario would be to have  a lot of both.  There's no accounting for the huge benefit of having thousands of hours of "deep practice" applying what's been learned at multiple years at University.  I remember when I was getting ready to graduate from PT school, my clinical instructor told me that while I knew a lot then (I have forgotten more information than I remember; you get so crammed full of data in PT school) it would take about 4 years of being out there and working to really "figure it out".  I wasn't sure exactly what that meant at the time, but sure enough after about 4 years I started to feel like I could fully trust my instincts when it came to mechanical assessment.  After that, reading someone's movement pattern was something I could do quickly by watching them repeat it (walking, lifting, throwing, whatever) only couple times instead of pouring over video for 10 or 15 minutes.

Interestingly, I discovered, years later, that the four years of practice actually lined up with what researchers have found when studying what it takes to become "expert" at something.  Whatever the task, (shooting a basketball, programming a computer, playing the piano) spending 10,000 hours in dedicated practice of this task can make you as close to an expert as you're likely ever going to be.  Working 4 years at roughly 2500 hours per year -- the math is about right.

4.  Bike Fitting at its core is about Balance --  This can refer to weight distribution on the bike fore-aft -- having the right amount of weight on your hands, feet, and butt -- as well as lateral balance -- most clients are surprised to find out that they don't sit in the center of their bike.

I would argue that this balance can refer to the symmetry and smoothness in a balanced pedal stroke -- one without a hitch or hesitation anywhere through the cycle.

In another vein, the bike fitter must also balance the cyclists physical profile (their flexibility, their strength/stability, their movement patterns) with their positioning on the bike.  One common and very simple example of this that I see is when I have to find the correct bar height that will match the cyclist's pelvic position on the saddle -- once we get the right saddle height and have it's fore-aft adjustment set (we've determined that optimal position of the hips relative to the feet) everyone's pelvic position (and spinal mobility) will dictate where the most balanced place will be for the handlebar placement.

5.  Small corrections!  Bike Fitting is a task of the millimeter, not the inch. -- I am continually amazed at how pronounced even very small changes to contact points can make such a measurable and drastic difference.  Sometimes you need to go big, and when you do, you need to make sure it's not causing other problems, so make sure it is easily undone or walked back if problems arise.

6.  Any bike fit worth it's money needs to be dynamic -- forget the plumb lines, goniometers, and tape measures.  You need to be looked at and have the measuring take place while you're pedaling.  Stopping your pedal stroke to measure -- bad!  Video assessment is fair....using it to "look"  that is, not measure.  The margin of error on measuring with video is on the order of +/-10%, so it's sensitivity is less than exceptional, but a skilled eye may be able to use it to pick out a few problems (see #7 for more).  The infrared used in the Retul system is ideal, since it's dynamic (it measures you while you pedal) and it's hyper-accurate (+/-0.2mm), and measures in all three cardinal planes (thus it renders lateral movements as well) it's the gold standard for measuring.  Notice that I said it was the best way to measure -- having this technology doesn't guarantee a good bike fit.  Since all the Retul does is provide data (very good data), it's still necessary to have a skilled fitter interpret the data.

7.  The trained human eye is a very good but limited tool. -- I'll go on record as saying that it is very important that a good bike fitter does use their own eyeball to help make decisions.  No one should rely entirely on a machine (like the Retul) when performing a bike fit, and the trained eye is great at picking up when something is wrong -- or right.  The trained eye may not be able to tell you what is wrong/right, by how much, and even in what direction something is deviating.  It's great at recognizing patterns or subtle hitches, and at this point in my career one of the times I always use my eye as the final arbiter of when we're done or when we have more work to do.  The machine should never make decisions -- it should only measure a provide data with which to make a decision.

8.  There are no "Have To"s -- There is a lot of bike fitting mis-information out there.  Some written, some just passed along in the verbal tradition from cyclist to cyclist and much of it is pretty bad.

You can see your front hub above/behind your handlebar when you're on the hoods?  Terrible.

You're knee doesn't fall directly over your pedal spindle in the 3 o'clock position?  Ugh, you're in trouble.

These are just two of the many old wives tales and urban legends of the bike fitting world.  There are no absolutes in bike fitting -- sometimes it's in the best interest of the cyclist to have a part of their fit fall outside of the "normal" parameters.  Pick whichever cliche you'd like:  we're all different; no one is completely normal; we're all individuals.  Not everyone falls within three standard deviations of normal, so why do some bike fitters try to wedge everyone into the same box on the bike.

9.  Formulas don't work. -- For the same reasons of individuality as mentioned above, no formula can take into account the vast differences  that exist among cyclists.  Even among similarly sized and built riders, you'll find significantly different optimal fit positions.

1 comment:

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