Is Your Bike Fit Hurting You?
Question: I recently decided to get properly fitted to my bike. So I did a Google search to see where to go, and also asked a few friends. In the end, I was more confused by all the different offerings than I was before. How do I find out who to go to, and which system is the best? – Thabo, Johannesburg
Doctor Jeroen Swart: I feel your pain, Thabo. Until recently, bike fitting was an area based on lore and tradition rather than validated scientific principles. Luckily, science is catching up; and there has been some particularly good research conducted by Wendy Holiday, a UCT researcher at our own Sports Science Institute of South Africa.
In terms of scientific evidence, the area that has been researched well is saddle height. Some systems use your inner seam measurement to predict the correct saddle height. These are generally a poor choice, and scientifically proven to be wrong at least 73% of the time.
Shooting From The Hip
Using trochanteric leg length is a more effective method. On the outside of the leg, measure from the bony protrusion at the hip (greater trochanter) to the base of the heel. This should always be done while you are sitting on the bike; the fitter will stop your pedal stroke at the bottom, to check the position of the knee.
Using the Holmes method (in which the pedal is placed in the horizontal position), your knee joint should have a range of flexion of 25 to 35 degrees. This has been shown to have the lowest risk of injury, and provide the highest power output and best economy (lowest oxygen consumption).
The question of how far forward or back the saddle should be has not been investigated as thoroughly. But Raymond Teo, also of the Sports Science Institute, conducted research into this topic recently.
Moving the saddle forwards will result in your quadriceps (front of your thighs) working harder; while moving the saddle backwards means you use your gluteals (buttocks) and hamstrings (back of your thighs) more. Which is best for you depends on many factors: the discipline, your experience, the distance being ridden, and others.
Once the saddle height and fore/aft position adjustment has been done, things start to get very sketchy. There has been little to no research on how to achieve the best hip, torso, shoulder and elbow position. We do know that extremes of hip position reduce economy (i.e. result in more oxygen consumption). So an overly aggressive position (long distance to handlebar, and low handlebar) will cause problems – as will an overly conservative position (sitting too upright).
Some bike brands (Specialized Body Geometry, Retul, ErgoFiT, and Shimano Bike Fitting) have developed their own commercial systems, having conducted in-house research that provides reference ranges for the joints mentioned. But these research findings have not been published, and you therefore have to go on faith or reputation that they are accurate and work well.
Other than using these systems, a fitter can also call on experience. This may sometimes look like voodoo, but there are some really good bike fitters out there who don’t rely on any specific system, but still achieve excellent outcomes.
There are also some very promising new technologies being used to optimise bike fitting. One of these is dynamic saddle-pressure mapping. Translated, this is the measurement – while you pedal – of pressure in the various areas under your tush. Seems like a strange way to do a bike fitting, but it works!
A Successful Fitting
A good fitting will start with a thorough interview, which will map out your history and goals. This should then be followed by a thorough examination that takes into account height, limb length, and flexibility. These measurements are used to generate a predictive report before the bike is adjusted.
You may experience some minor niggles in the first week or two after the fitting. But after that, you should feel better than you did before.
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