Redefining the definition of bike fitting

Type "bike fitting” in to Google, and you will most likely get more the 7 million hits. But what does bike fitting actually mean? If you were to ask the average bicycle retailer, you would probably get an answer something along the lines of setting up the seat height. On the other hand, if you were to ask a sport scientist the same question, you should be enlightened to the following definition: "Bike fit is a process of changing body position by adjusting bike parts to achieve an interaction between a number of variables – such as exercise economy, mechanical/metabolic efficiency, and comfort – to minimise resistive forces and maximise bicycle velocity while at the same time reduce the risk of injury occurrence.” It sounds very complex and difficult to comprehend but, in reality, it is very simple: a bike fit should make cyclists faster, safer and/or more comfortable. Although the aims are clear, the process of actually undertaking a bike fit is not that simple. 

As a concept, bike fitting interacting more and more with different technology such as motion capturing systems, laser body measurements, etc. But how does that technology actually fit into the process of bike fitting? Well, everything started when Hamley & Thomas (1967) published their results and linked the optimal seat height with the inner leg length. This was furthered by other researchers and for a long time static measurements of body anthropometrics stood as a standard in bike fitting. Later, Holmes, Pruitt, & Whalen (1994) provided a more detailed method, a knee angle measurement when the pedal reached the lowest point of the crank cycle, and stated that this angle should fall between 25 and 35° measured with a manual goniometer. This method reportedly reduced the load on the knee joint. Furthermore, a research group from Canada showed that seat height at the higher end of this range (~25° knee angle) provides more power and increases economy of riding (Peveler, Pounders, & Bishop, 2007; Peveler & Green, 2011).  


Some of our work questioned the use of static knee angle measurements in the process of adjusting the seat height, mainly due to the error one can exhibit by just lowering the heal, twisting the spine or bending to one side. Our published work (Fonda, Sarabon, & Li, 2014) demonstrated that there is a significant difference in the knee angle when measured with different methods. The results showed that a valid measurement can only be achieved with a 3D motion capturing system that records data with 50 Hz or more. 2D high speed camera would suffice if you add 2.3° to the measured value. Based on these results, you should set up the seat height to achieve the knee angle between 33 and 43°. Or should you? 

The afore mentioned is all well and good, but do we all perform in the same way? A great cycling biomechanics researcher, Rodrigo Bini, asked if we should seek generalized standards in bike fitting based on kinematics (Bini, 2013). Moreover, the 10° range is actually quite big and can mean a difference up to 2.5 cm when setting the seat height. This issue was our main aim in the development of a bike fitting system - how is best to fit a cyclist to improve his or her mechanical effectiveness without instructing them to pedal differently? We know that seat position plays an important role for mechanical effectiveness (Bini, Tamborindeguy, & Mota, 2010), thus the answer is relatively simple: we can achieve this with a direct measurement of mechanical effectiveness.  Whilst this sounds very simple, in order to get the complete picture the hardware has to allow measurements of the forces around all three axes, crank position and pedal angle.


Furthermore, to evaluate bending and rotation of the foot you also need moments around two axes. Adding 3D kinematics to get the cyclists motion information nicely wraps up this bike fitting approach. We are delighted to be able to put this comprehensive and unique system to the market.

Please take a look at our web page for more information and do not hesitate to contact us if you have any questions. We strongly believe this is a big step forward in the field of cycling biomechanics and will serve to dramatically upgrade the meaning of the phrase ‘bike fitting’.  


Borut 

References:

Bini, R., Tamborindeguy, A., & Mota, C. (2010). Effects of saddle height, pedaling cadence, and workload on joint kinetics and kinematics during cycling. Journal of Sport Rehabilitation, 19(3), 301–314.

Fonda, B., Sarabon, N., & Li, F.-X. (2014). Validity and reliability of different kinematics methods used for bike fitting. Journal of Sport Sciences, 32(10), 940–946. http://doi.org/10.1080/02640414.2013.868919

Hamley, E. J., & Thomas, V. (1967). Physiological and postural factors in the calibration of the bicycle ergometer. The Journal of Physiology, 191(2), 55P–56P.

Holmes, J. C., Pruitt, A. L., & Whalen, N. J. (1994). Lower extremity overuse in bicycling. Clinics in Sports Medicine, 13(1), 187–205.

Peveler, W., Pounders, J., & Bishop, P. (2007). Effects of saddle height on anaerobic power production in cycling. Journal of Strength & Conditioning Research, 21(4), 1023–1027. http://doi.org/10.1519/r-20316.1

Peveler, W. W., & Green, J. M. (2011). Effects of Saddle Height on Economy and Anaerobic Power in Well-Trained Cyclists. Journal of Strength & Conditioning Research, 25(3), 629–633.

Rico Bini, R. (2013). Should We Seek for Generalized Standards in Bike Fitting? The Journal of Strength & Conditioning Research, 27(3), E1 10.1519/JSC.0b013e318260061b.