The Science and Art of Bike Fitting

Bike fitting has existed since the invention of the bicycle in the mid-1800s.  However, the science of fitting has evolved considerably faster in the past 30-40 years.

Ancient Rules of Thumb (also called “old wives’ tales”)

Coaches and cycling experts in Europe, and particularly in France and Italy, have been using a rules of thumb based on tradition and lore that date back hundreds of years.  Essentially, these rules of thumb were based on what was observed to work “for most people” in loose size brackets, and are still widely used today.  An assumption has to be made when using these rules that people are statistically “normal,” in the sense that all their limbs are in proportion to their height. In fact, no one fits this mould!

Static Fitting

Only 30 years ago a system called the Fit Kit was introduced.  It is still in used today and prescribes a set protocol where various lengths on the body are measured.  The numbers are then multiplied by ratios, much of which were based on the Rules of Thumb described above. The Fit Kit was unique when it was introduced in that it allowed any salesperson in any shop to at least be able to provide a reasonable target for bike size selection and placement of the contact points to the body. Other systems that would fit the description of a static fitting protocol are those by Body Scan, Carmichael, Cyfac, Serotta, Specialized BG Fit, and WobbleNaught.

Dynamic Fitting

The term “Dynamic Fitting” can be used to refer to two distinct types of bike fit: dynamic positional changes, and dynamic motion capture.  A dynamic positional fitting is one where settings (like saddle height) are dynamically altered during the course of a fitting session.  Parameters like comfort, aerodynamic efficiency, power output, heart rate, and blood oxygen saturation are then assessed using a variety of methods after each “dynamic” change to determine an optimal setting.  The FIST protocol developed over the past 20 years by Dan Empfield is an example of a dynamic fitting protocol.  “Dynamic” is also sometimes used to refer to the capture of data from a subject while he/she is moving, though this is better viewed as a separate step in the evolution of bike fitting, better referred to as “Motion Capture.”

 
Motion Capture

Motion capture systems are becoming prevalent at the elite level in all sports.  As sport scientists better understand human biomechanics and the ranges of motion that the human body operates within, it makes sense to use the technology available to follow and track the human body so that it can be quantified, analyzed, and optimized. This technology is similar to that used to create video games and CGI movies, and is often expensive.  Kinovea and Dartfish are two video-camera-based motion capture systems that are used in cycling.  Retul is an example of a camera/LED-based motion capture system that is cycling-specific.  It can be used to provide real-time data display and tracks human motion in 3 dimensions, whereas video-based systems are two dimensional. 

It should be noted that Motion capture systems are really “just” a tool for the bike fitter. However, Retul technology was developed by experts in cycling-specific human physiology and they have developed a compressive fitting protocol that is tailored to the advantages it provides. 

A fitting at The Bike Energy Lab might draw on many aspects of this evolution, but with considerably more weight placed on the last two. No two people are alike, and the two latter methods lend themselves well to a good customized and optimal fit. 

There is much more to a Bike Energy Lab fitting than just the technical aspect, however.  Science brings us an understanding of how the body operates, and the rationale for a number of positional enhancements.  Technology is required to understand how the bike and its components work, and how they can be best used and manipulated to provide the best fit.  But there is also an art to combining these elements, and ensuring that the result is effectively communicated to the customer.