As bike fitters, we can generally agree to hold two seemingly opposing concepts in mind at the same time:
- All cyclists are individuals and need to be fitted according to their unique presentation, background, and needs
- Cyclists who function well on their bicycles will look similar in their position and movements.
When we view a cyclist who “looks good” on their bike, what we see is a pattern of body proportions, body posture and position, joint angles, and movements. When we see someone riding around who would obviously benefit from a bike fit we are also recognizing a pattern, but a different one.
One of the key skills of bike fitting, although it may not be commonly discussed, is pattern recognition. This can be based on subjective evaluation or measurement. A well known example of a measurement based, data driven pattern recognition system used by some bike fitters is the Retul motion capture system and the normative movement ranges it defines. There are also many other patterns “recognized’ in bike fitting, some based on observation and some on measurement. Experienced bike fitters recognize when a cyclist has their saddle notably too high or low, or too far back. Likewise when we see a cyclist with handlebars poorly situated. There are many small factors that contribute to the overall presentation and function of a cyclist riding a bicycle, but we assess all the inputs and summarize the findings as a pattern.
Pattern recognition is how our brain derives meaning and makes decisions from the overwhelming number of sensory data inputs we receive. It is a way to create order out of chaos, and in essence, it is a survival mechanism. Pattern recognition is also the basis of the newer sciences of machine learning and artificial intelligence, which might give you a sense of how important it is.
We also know that there are exceptions to every rule, which is why fitting by formula has a poor reputation. However a formula is another name for a pattern, and it’s not all bad. It’s only bad if the formula or pattern is not interpreted and applied with respect to the individuality of the cyclist. A common approach to bike fitting is to commence by understanding and working with patterns, and then individualize the fit from there, so as to cater to that unique person. To do otherwise is to try and perform a fit with no reference to history, experience, and other cyclists.
In this article, I want to share some of the fitting applications based on body patterns that I have observed, measured, and analyzed. I’ve been taking body (skeletal) measurements of cyclists for over 15 years, and after a while, I started to observe recurring themes with implications for both understanding the fit issues the rider was experiencing, and what interventions helped resolve them. I’m far from the first person to do this but the work of our bike fit pioneers and innovators sometimes gets lost in the rush to embrace the latest and greatest approaches and technology. Not all that is old is outdated, and fresh insights can add value to old practices. Body measurement data is very useful – if you know what to do with it.
Body Measurements and Bike Fitting
People have assuredly been evaluating and measuring bodies for as long as there have been bicycles to ride. If we take the publication of the manual on Cycling by C.O.N.I in Italy in 1972 as the start of the modern era of bike fitting, it makes reference to body measurements, equipment selection, and fit position. Notable French Sports Director Cyrille Guimard used body measurement information with his famous protégés: Bernard Hinault, Laurent Fignon, and Greg Lemond – whose oft-referenced seat height formula is based on a body measurement.
Following this, mathematician Bill Farrell who founded the New England Cycling Academy (NECA) and then Fit Kit Systems dug deep into body measurements to originate the first Fit Kit protocols, and similar work was done in Europe leading to the development of the Cyclefit system, now owned by Innovative Cycling in Belgium, and Bikefitting.com in the Netherlands, now owned by Shimano. These early pioneers designed and used hand tools to take physical measurements of riders. More recently, Trek, Cannondale (under the Guru brand), and Specialized as well as others have attempted to deploy technological tools to derive digital measurements of people – with varied results.
What Is Measured?
The principal body measurements taken with the Fit Kit System are foot length, inseam length, torso length, and arm length. That is just 4 measurements. Other body measurement systems may include different or additional anatomical features, for example:
- Floor to sternal notch
- Upper arm length and forearm length
- Femur length and tibia length
- Shoulder width
- Sit bone width
- Hand length
The landmarks used to define the start and end of the measure may also vary, so there is not a tightly defined methodology. Hence there is risk in transferring the measurements from one system to another.
What Have Body Measurements Been Used For?
Obtaining body measurement data by a measurement method is only the first step. What is of significance and relevance is how the data is interpreted and applied.
Body measurement data has been used in a number of bike sizing and fitting applications in the past, such as:
- Determining seat height
- Selecting a frame size
- Estimating bike length, expressed as a combination of effective top tube and stem
- Estimating cockpit dimensions of reach to the bars, saddle-to-bar drop
- Selecting crank length
- Recommending a seat tube angle
These are not the only applications for body measurement data. There are more!
Bike Fitter Attitudes to Body Measurements
Bike fitters are not universally exposed to body measurements, or the different ways they can be used, as this will depend on their bike fit training and exposure to ideas and methods. Some influencers, who have never actually used body measurement data, say they are of no relevance and use, pre-judging the outcomes based on the method.
Because the use of body measurements have been around since the early days of modern bike fitting, many fitters dismiss their use as “old school” and therefore outdated and irrelevant. The creation and use of 2D and 3D motion capture systems in bike fitting, as well as other innovations has led to an uptake in newer technologies and a subsequent drop off in the use of older technologies
Bike fitters have either:
- Never been exposed to and trained in the use of body measurements
- Used them in the past but view their use as outdated and no longer applicable to bike fitting
- Received education in the use of body measurements and used them as an additional layer of data and perspective to help resolve fit issues.
However, those fitters who are not using a body measurement system are still “sizing up” a rider by eye, and consciously or not will be assessing their body pattern and the relevance to the fit. The benefit of using a measurement system is that any subjective assessment is quantified by using hard data based on actual measurements.
How I use Body Measurements
Fit Kit Systems was one of the early pioneers and promoters of using body measurements. Some fitters quickly found benefits to using the “Fit Kit” measurement system. Others remain doubters to this day, giving little thought to the intervening 40 years and progressive developments in understanding bike-body relationships, including advances in understanding human anatomy and biomechanics, and changes in bicycle design. In my 15 years of using the Fit Kit to measure thousands of people, and performing bike fits, I have come to understand these measurements can provide a trove of information. This information can be used to enhance understanding of a particular cyclist and what the comfort or performance issues are on the bike, and give clues on how to resolve them. I do not use body measurements in isolation but add them to a layered understanding of the cyclist. By taking a systems approach to the cyclist, and considering them from multiple layers and perspectives, a deeper understanding can be gained of the bike-body relationship, leading to better outcomes for the rider.
I view the skeletal information gained from body measurements to be the foundation level on which the other information is layered. To leave it out is to omit an important viewpoint of the cyclist which may be significant in understanding their relationship to the bike.
The skeleton is the foundation layer of the body and the layer that body measurements are paying attention to. As muscles attach to bones, which are the levers for motion – the bones determine the first limitation (or potential) of movement. This is further nuanced by understanding a cyclist’s body pattern, and other limb length relationships.
The soft tissue includes additional body systems: muscular (muscles, fascia, tendons, ligaments); nervous; and vascular. We could add respiratory and gastrointestinal as well. Injuries and issues may be at the skeletal level (eg broken bone, hip occlusion) but are often at the soft tissue level. Soft tissue assessments include muscular strength, mobility, and stability as well as injury history.
The upper layer of considerations includes the cyclist’s riding history and experience, and their near and long-term riding intentions, aspirations, and goals, as well as the type of bike and the fit-related components which they are interacting with.
None of these perspectives on their own provide sufficient depth to fully evaluate the cyclist and make fit adjustments and recommendations. However, taken together we can use a “whole of body” evidence-based approach to proceed through a fit session.
By The Numbers
As with any measurement system, it can take a while to get familiar with the numbers, and what they mean. Taking five minutes to measure someone with the Fit Kit gives me a set of numbers to reference, and from experience, anything of significance will immediately jump out. The following table is provided to give some sense of the range and relative proportions. All measurements are in centimeters.
|75 – 80cm
|50 – 55cm
|50 – 55cm
|25 – 28 cm
|55 – 60cm
|55 – 60cm
|60 – 65cm
|60 – 65cm
These descriptors are general terms with size ranges selected based on observation and convenience, not statistically significant ranges. Furthermore, the numerical ranges as based on the use of the Fit Kit tools and method of body measurement, and this may not be the same as those of other body measurement systems. Gaining the body measurement data is only the first step. What is of significance and relevance is how the data is interpreted and applied.
3 Primary Body Patterns
What I find most informative from the skeletal layer are the body patterns, and these are based on the relative relationships of one measurement to another. I’ve identified primary and secondary body patterns using the basic Fit Kit body measurements, that have implications for how the person fits on and operates a bike. Users of other body measurement systems may have identified similar or other patterns and insights.
The primary body patterns are about identifying (from measurement) the relative proportions of the rider from floor to sternal notch, divided between inseam length (floor to crotch) and torso length (crotch to sternal notch). This is independent of the height of the rider but is relative to their own height.
The following use of terms long and short do not refer to the ranges in the previous table but are about the RELATIVE proportions for that individual. For example, a torso-dominant person described as having a long torso and short legs might have legs in the long range and a torso in the medium range. What is relevant in this case is the relationship between the body parts, not the absolute measurement.
Torso dominant riders have more weight to distribute horizontally along the bike than leg dominant riders. They often present as too scrunched up (hunched shoulders, rounded back) as their long spine cannot extend out. This is especially so if they have been sized for a frame based on inseam only. A common pitfall in fitting this rider is to simply lengthen the front end of the bike (larger size or longer stem), but this can make them front heavy, leading to hand numbness or shoulder and neck tension. The key is to get their center of mass balanced along the bike, which often means more saddle setback to move the pelvis further behind the bottom bracket. Their spine needs space to open up and extend along the bike.
The more pronounced the dominance, the more of an outlier they are. The relatively short legs would be happier on a smaller frame size, but the long upper body wants a larger frame size. Hence there is often some sort of compromise. This will typically be in the form of a smaller frame to achieve a satisfactory standover clearance and saddle height, but a longer stem, bar reach, and more saddle setback to distribute the upper body weight along the bike.
Torso dominant riders without restrictions in mobility do well on race geometry road bikes which are also low and long.
Summary: Lower seat height, longer reach, more saddle setback. Caution: stand over clearance may be an issue.
This does not mean average, but these people are “middle of the bell curve” and that is the body pattern bikes are designed for. Hence there are fewer intrinsic mismatches between the bike and body.
Summary: Relatively easy to size and fit. Skeletal measurements have less influence on the fit.
Leg dominant riders have a bias toward leg length making a significant contribution to overall height. If a leg dominant rider is sized for a frame based on inseam length only, the bike will often be too long for them, as they don’t have the torso length to reach out along the bike. This can lead to the rider being too stretched out.
The leg dominant rider will show more seat post with their saddle at an appropriate height relative to a balanced or torso dominant rider. A consequence of this is a much greater saddle-to-bar drop. Whether this is appropriate will depend on their mobility, arm-torso ratio, and overall arm length.
A historical use of body measurement data in bike fitting was to say that a rider with longer legs needed more saddle setback. My experience indicates the opposite. A leg dominant rider has a relatively short torso, so less mass to distribute above the saddle, and less spinal length to reach out to the bars. As dealing with gravity is a higher order of priority for the body than propelling the bike, getting the rider balanced over the bottom bracket and the saddle situated to support that position usually means less saddle setback and a shorter stem. This is from the skeletal perspective, which of course can be influenced by other factors. Performance-focused, leg dominant riders are often positioned too far behind the bottom bracket and can get saddle issues as they move forward onto the nose of the saddle in order to get over the pedals more effectively.
Summary: Higher seat height, shorter reach, less saddle setback. Caution: needing a stem too short to make the bike fit comfortable; seat post extension insufficient.
2 Secondary Body Patterns in Bike Fitting
Foot and Inseam
An inseam measurement is a traditional approach to estimating a saddle height for a rider, and by that I mean establishing a rough in, or starting position. Many shops and fitters still use this, and commonly reference to what is referred to as the Lemond Method, being saddle height from BB = 0.883 of the inseam measurement. But what about foot length? Ask yourself this question: would two riders with the same inseam measurement but with feet 2 or 3 sizes different end up with the same saddle height? Not likely, as the foot is part of the lever the bridges the gap from pedal to saddle. Taking foot length into account helps refine the saddle height projection. A longer foot suggests a higher saddle. Of course, there are other variables at play, but this is an important one.
Arm to Torso Relationship
In addition to identifying the Primary Body Pattern, an understanding of the Arm to Torso ratio provides an additional layer of insight. Instead of looking at the arm: torso relationship as a pure ratio, I look at it as a pattern, for which there are three.
These people have long arms relative to their torso, often described as a big wingspan or a high ape factor. This is a useful trait for a rock climber. From a cycling perspective, if the arms are significantly longer than the torso, the rider typically prefers an increased saddle to bar drop. The arms have to live in space somewhere, and they have a preference for hanging out in the vertical plane, rather than the horizontal plane. That means a rider with a positive arm to torso ratio will typically prefer to have more drop than more reach to the bars.
A great way to misfit a rider with this body pattern is to increase their reach to the bars and decrease their saddle-to-bar drop. Hand pressure and shoulder tension will increase.
This pattern is more prevalent in men, but there are plenty of women with a positive arm-torso ratio as well.
One to One
A one-to-one ratio of arms to torso is by far the most common. Again, this is a middle of the bell curve presentation, with no particular considerations to keep in mind.
Arms significantly shorter than the torso. This pattern is much more common with females, who also statistically have shorter arms in general than males. This has significant implications for bike fit. Bearing in mind that the arms have more influence vertically than horizontally when it comes to bar position, shorter arms in general, and a negative arm to torso ratio, in particular, means the bars need to come up to meet the hands. On a road bike, this will show up as very little or no saddle to handlebar drop, or even bars higher than the saddle. On mountain bikes, this is exaggerated, as the width of the bars is also using up available arm reach, and so the bars need to be even higher.
Performance-focused women riding road bikes with a set up similar to men (i.e deep saddle to bar drop) often suffer from chronic saddle pressure issues. My hypothesis: a contributing factor is that the bars are too low for their arm length, leading to overrotation of the pelvis to reach the bars and resultant overloading of the genital area = too much pressure where it is not welcome.
What I have highlighted here is the big picture or more significant patterns. Other fitters may be paying attention to more nuanced patterns like the femur to tibia relationship, and the forearm to upper arm relationship, both of which have implications for fit. There is plenty to explore and pay attention to when body measurements are taken, and patterns emerge.
Taking Body Measurements of a cyclist is a quick and easy way to gather data about the cyclist’s skeleton on a few key metrics.
Identifying body patterns from the measurements, AND viewed in relation to all the other information gained about a rider, they can be used to help understand why a cyclist may be experiencing particular issues, and if:
- Saddle height may be out of range (too high or too low)
- Saddle setback is too forward or back. Saddle setback is critical to weight distribution and balance on the bicycle.
- The combination of handlebar reach and drop is appropriate.
- The cyclist is compensating too much in a position. Is it sustainable for them?
The same measurements and patterns can be used to set up an adjustable Fit bike with a starting position for a rider. You have to start somewhere with the settings on a Fit bike. One approach is to start way out of range with some extreme settings and dial it in from there. My approach is to start with a conceptually good position and refine from there. But that is another article!