I have done several articles on how helpful Dartfish is during the bike fitting process.
One of the features I am using now is vertical lines under the Analyzer. This allows me to quickly check the clients knee over pedal axle (KOPA) measurement. I placed markers on the client’s shoes which show where their shoes/cleats are in relation to the pedal axle and crank arm. The vertical lines in Dartfish, which I can change color and thickness, makes it quick and easy to see whether I need to move the saddle forward or rearward.
In the photo below, the purple markers indicate where the center of the knee is in relation to the pedal axle.
BELOW – A new metric I am looking into and testing is for saddle fore/aft. I stopped the video at the frame where the client is at max extension and I placed several Dartfish markers on the screen.
Aside: There are 3 pivots that the leg must rotate through during a complete pedal rotation; (a) the Greater Trochanter which is the top ‘pivot’, (b) Lateral Condyle which is basically the center of the knee and (c) Lateral Malleolus also known as the ankle bone.
If the cyclist is sitting too high in the saddle, then they will have severe hip rocking as they try and reach the pedals. If they are too low in the saddle, then there is excessive strain and stresses on the knee due to hyperflexion.
One quick metric to see if the cyclist is in range is to stop the video while the cyclist is at max knee extension and place markers at the following locations; (a) Greater Trochanter, (b) Center of Bottom Bracket, (c) two reference points that would indicate a line parallel to the ground.
Then, using the angle tool, determine the angle of the Greater Trochanter through the Bottom Bracket and then parallel to the floor. If the cyclist is adjusted core/aft correctly, this angle should be close to the seat tube angle of their bicycle. In this case, the cyclist’s angle is 73.0 (Fig 2), their bicycles seat tube angle is 73 (Fig 3).
Dartfish is a great multi-dimensional tool that has proven a great time saver during the bike fitting process.
In this pdf, discover some examples of how the technology can be used to enhance a bike fit.
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