I hope everyone has been enjoying the Tour this year! I am still personally hoping Sagan can steal a stage win to add to his pair of second place finishes!
Professional cyclists demand the most out of their machines because they want every advantage against the competition and the clock they can get. As a former professional cyclist that competed for and against Pro Tour rides in international road and stage races for 3 years, I had the opportunity to learn from the best. In my experience once a rider dialed in his or her time trial fit it would never change regardless if the distance was a 3km prologue versus a 55km individual time trail.
The Union Cycliste Internationale has a rule for all TT bikes that the nose of the saddle must be a minimum of 5cm back to a perfectly vertical line passing through the center of the bottom bracket. All riders stick to this rule and there is only a performance disadvantage of going farther back then 5cm because you will begin to decrease your hip extension moment through the femoral acetabular joints frontal axis and therefore lose power. Afterall the gluteus maximus is a hip extensor/external rotator muscle and the position of 5cm back will allow a rider to best fire this muscle when pedalling.
Some individuals are under the impression that bike position should change based on distance. So what might they do? Not sure, I would be curious to know and why? Dropping the saddle could be beneficial perhaps. There is biomechanical research that exists proving that if your hip, knee and ankle joints do not have to extend through an absolute full range of motion you are able to produce more angular acceleration of your legs (faster cadence). One reason why we all slide up onto the nose of the saddle to go fast! This increased acceleration of the legs, increases the electrical activity of the gluteus maximus therefore engaging the glute better so the rider is able to use it more during a TT pedal stroke. Think of runners with fast cadence such as sprinters, they definitely have bigger glutes then marathon runners. I have two problems with lowering the saddle however, one you eliminate the optimal length/tension relationship on the quadricep muscle (the primary power generator for pedaling)and two you dramatically increase the shearing force at the patella-femoral joint which can cause anterior knee pain. In my fits, I have found that educating a rider about their 1st, 2nd and 3rd gear on the saddle can do the same thing without lowering the saddle.
What about aerobar drop? Sure you could slam their stem/bar combo as low as possible to cheat the wind, but then you are going to create more thoracic kyphosis, scapular elevation, and humeral flexion which will tighten your latissimus dorsi, (lats are a scapular depressor, humeral extensor and external rotator) therefore acting like a straight jacket around your chest and not allowing the athlete to breath! Additionally dropping the stem/bar combo will increase the anterior pelvic tilt and pressure on the inferior pubic ramus which can compress the deep and superficial perineal nerves. I have never met an cyclist who liked when their genitals went numb!
Since I have been out of the pro pelaton for a few years, I did call a good friend of mine who currently races in the Pro Tour for UHC and has completed the Giro when he rode for BMC in 2010 & 2011, he also used to be a bit of a prologue specialist but now is a classics rider and has finished Paris Roubaix twice! He told me none of his teammates on UHC or BMC or any other Pro team he has ever ridden for switched their TT position based on distance and these guys have the benefit of wind tunnel testing several times a year!
Do the above rules apply to the everyday athlete, no. For amateur athletes not fit enough to hold the aero position for 55km or above we would definitely raise the aerobar position, but that doesn’t really matter because narrow is aero and we can teach you to tuck in. Think for example what catches more wind in a wind tunnel? A refrigerator or a 1 inch diameter metal fence post twice as tall as the refrigerator?
Triathletes racing 90-180km have a much different set up absolutely. There is no rule in the Triathlon world regarding fore-aft seat position in relation to the bottom bracket. Depending on the size of the rider you would typically run the nose 2-3cm back from the vertical line, again to further emphasize the extension moment at the hip. Farther forward then that and you create a situation where there is unequal weight distribution between contact points on the bike and you can get numbness in your forearms and hands. One of the most beneficial things I teach my triathletes is attention to detail regarding how they pedal, and to fix the dead spots in their pedal stroke so they are not over working on the bike and zapping their legs for the run.
Bike fitting is not an exact science, but an evolving science!
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