Bike fitting: Science, Art, Tech or Pseud?

I stumbled across a little video on social media.  A cycling ‘influencer’ was extolling the virtues of his bike fitting, proudly relaying the things that he’d learned while the video itself showed him on his bike in the fitter’s studio.  

Everything that he said was spot on:  back relaxed, shoulders down, arms bent, light grip on the handlebars, supported on the sit bones, power from the glutes…

Everything that he demonstrated, however, was the complete opposite:  back as stiff as a board, shoulders forced up, weight on the perineum.  His fitter was walking around him reminding him to keep his arms bent and his back straight.

He’d also learned from the fitter that being aero was ‘not important’.  That’s just as well, because he was far from aero.  

I don’t know who was in the bigger state of denial.  The cyclist or the fitter.  The fitter had dutifully followed all of the rules and now it was up to the cyclist to do his bit and follow them too.  They were both trying.

I’ve posted before about rules-based bike fittings and the problems with fitters and systems that just follow a set of rules.  But if there are no rules or parameters what defines a good fitting?  Is it just an art?  Artists who draw or paint realistic pictures follow a lot of rules:  perspectives, shadows, scale, colour, texture…  Composers and musicians who create popular pieces follow a lot of rules too:  key signatures, scales, intervals, harmonies, rhythms…   The finest artists don’t just know the rules, they understand them; they don’t follow them blindly but somehow they work within them.  

Yet every picture and piece of music that they create is different.

Bike fitting has its rules too.  But those rules are fundamentally physics and bio-mechanics.  Gravity pulls you down and the bike holds you up – so the bike has to support your entire bodyweight.  In the world of physics (i.e. the real world) a body is stable if its centre of gravity is above and within its base, but the proportion of the load supported at different points on the base depends on where the centre of gravity is.

When you’re on your bike those points of contact that support your entire bodyweight are the pedals, the handlebars and the saddle.  Or, if we consider you (the rider) rather than the bike, the points are your hands, the balls of your feet and the three parts of your anatomy that come into contact with the saddle which are your genitals, your perineum and your ischial tuberosities (your sit bones).  Of those, only your feet (and remember that it’s the balls of your feet that are supported, not your heels) and your sit bones tolerate weight well.  The others really, really don’t like it.  Ever wondered why you want to stand up on the pedals (with your heels down) or push yourself onto the back of the saddle when you get tired?  Whatever it takes to get your weight off those bits that don’t like it.  But as soon a you relax again the pressure all goes right back where you don’t want it!

Which brings us onto another bike fitting ‘rule’.  Avoid as much un-necessary tension as possible.  Pushing yourself back on the saddle, or standing on the pedals with your legs straight while you’re trying to ride are both unsustainable because you have to use a lot of muscles to re-position your centre of gravity and hold it there.  I’ve posted before about movement muscles and postural muscles before too.  

A third key aspect of bike fitting is that it enables good movement patterns.  Whilst your upper body should be relaxed and fairly static, your lower body has to turn the cranks in circles.  To do this the muscles in your legs have to work the joints in your legs.  Your bike doesn’t care how you do this – as long as you press down harder on the pedal at the front than the pedal at the back the cranks will turn and the bike will move forward.  But those muscles and joints are not all the same.  They have different strengths and different ranges of movement.  A good bike fitting enables good and sustainable movement patterns.

These rules of physics, tension and biomechanics are all at play in the relatively controlled environment of fitting studio.  It might be possible to measure them but I think that the technology has a long way to go before it catches up with a good eye.  But where they really matter is out in the real world where the environment is a whole load less controlled.  That’s when understanding the rules and not just following the instructions makes makes a good fitting a work of art.

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