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I recently came across the web site of a bicycle dealer who offers high quality Fitting Services, but was appalled by the misleading and downright incorrect information it spewed about Fitting methods they do not use.  This is not a local dealer, but since a few people outside the local area read this blog, I think it's important to get the facts straight.

Here's the relevant part of what their web site says: "…we can analyze actual video rather than the 'stick figures' used by other systems such as Retul, which is entirely dependent on proper body marker placement and shows only angles, not bodies!"  This dealer uses Dartfish, a 2D video capture system with associated computer software.

                                                      Dartfish screenshot

I won't bore you with lots of details, so here are the essentials.  Dartfish records a video of the athlete.  The video is played back on a computer monitor screen upon which "markers" are placed using the computer mouse/cursor.  The software generates lines between markers and displays the lines and calculated angles between them over the athlete's image (see above).  Very cool looking, very useful for many applications and fun to play with. 

Retul 3D Camera             Retul Sensor Harness             Retul

Retul does indeed rely on precise marker placement (Dartfish does too), but the Retul markers are placed on the actual cyclist after the Fitter palpates each key body joint (see above center).  Note that the LED used for measuring, about 1mm in diameter, is in the center of the larger black mount.  This direct application of markers makes more precise marker placement impossible (short of a full body X-ray).  Problems with Dartfish accuarcy usually arise because the markers are placed on a frozen video image that is only 2D and much smaller than life-size.  A marker placement error of more than couple of millimeters on the life-size cyclist is unacceptable – imagine how much error is possible on a blurred video image that is a miniature of the life-size original.

Retul measurements are taken over a Fitter specified time period as the cyclist pedals against resistance so a valid average is calculated.  In the real world, cyclists tend to move around a bit while pedaling.  Dartfish requires the user to arbritrarily select a single video frame (AKA make an educated guess) which may or may not be representative of the average pedal stroke of the cyclist. 

Last but not least important, and the reason I took notice of their web site – the "stick figure" (see above right) on the monitor display referred to is not used for determining measurements as they falsely state, it is simply a visual display to confirm correct system function.  Retul records measurements directly from the LED harness on the cyclist while they're pedaling against resistance.  Bottom line: Retul measures in real-time in life-size.

Any measuring system however is just a tool, like a hammer.  How successfully the tool is used depends completely on the experience and skill of the Fitter.  Wherever you shop for a bicycle be sure they have a Certified Fitter on board so your ride can be as comfortable and efficient as possible.

For additional info about Retul technology CLICK HERE.  For insights into the Fitting Process CLICK HERE.  BGI is proud to offer a variety of Fitting Packages appropriate for the real world variety or cyclist levels.  For additional info about BGI Fitting Services  CLICK HERE .