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The Keys to Bike Fitting

The central nervous system (CNS) controls every aspect of human function. The CNS controls our thoughts, movements, emotions, breathing, heart rate, body temperature and much more. How we perceive the world and how we interact with it is entirely centred around how our central nervous system operates.


All coordinated human movement starts with the intention to move from the motor cortex. The motor cortex notifies the cerebellum of its intent to initiate movement. At the same time, the cerebellum is continually getting fed billions of lines of information from proprioceptors all over the body. The cerebellum combines that intention from the motor cortex and the peripheral information it’s receiving to calculate the best possible movement pattern, combining the force required and balance needed. The cerebellum then relays this best option for movement to the motor cortex, which will then send that information down the spinal cord to the muscles to form a coordinated movement.


In any athletic activity, the central nervous system’s three fundamental priorities are, in descending order of importance:


1. Breathing

There are three energy pathways which fuel human movement. The body can only produce energy without the use of oxygen for a maximum of three minutes. As soon as energy requirements exceed that time, the brain and body need a steady flow of oxygen to allow them to function. Without adequate oxygen, a human cannot continue to function, and performance will rapidly decrease until oxygen supply meets demand. The human body is similar to a flame - starve it of oxygen and it dwindles.


The central nervous system will override everything to ensure the survival of the human. In a sporting scenario, this means the brain is going to limit physical performance to match the available oxygen or make compensations to the posture to increase oxygen availability or decrease consumption. This can be seen when athletes collapse down to the floor through exhaustion - forcing the body to stop working.


2. Posture

Posture is secondary to breathing. Posture can be thought of like the comparison between a corpse and a living body. Whilst alive - the CNS is consistently controlling muscles which enable us to hold our bodies up in relationship to gravity, without this consistent muscle activity we would be a bag of bones on the floor. Therefore, there is always a requirement to maintain posture. In terms of basic human survival, we cannot run or fight if we can’t hold ourselves up.


3. Movement

Movement comes third as the two above are required before movement can even be considered. As discussed in Breathing, without oxygen we cannot fuel our muscles, and without posture, we cannot hold ourselves in a position that allows us to move our muscles in any meaningful way. If posture significantly deteriorates during an activity we can easily topple over.


Movement ranks higher than other aspects of human function but the level of our ability to override it depends on numerous other aspects. Typically, you can only ignore your need to eat, sleep or drink when your brain is in “fight or flight” mode.


Every measure taken or intervention made during a bike fitting must be considered in relation to those 3 priorities and the order in which they are prioritised.


Every change planned can be referenced back to those three priorities. A bike fit that requires the athlete to hold and perform for over thirty seconds must make the bodies need for oxygen a top priority.


Working down the hierarchy, posture must be considered above movement. A poor posture that causes asymmetries or alignment issues will hinder the ability of the body to move efficiently. This could be a seat that’s too high, forcing the rider to sit off to one side, causing poor alignment of the pelvis.


As the desired outcome of a fitting is an efficient athlete, then an efficiently functioning central nervous system is fundamental.


If the information aiding the control of muscles isn’t clear, then movements may not be as efficient as they could be. Without a clear feedback loop, it’s incredibly difficult to coordinate your actions consistently. Imagine shooting at a target but not being able to see where the shot has landed. If you can’t see the result you can’t make corrections to the input to get a better output.


The key determinants of central nervous system efficiency are posture, alignment and functional symmetry.


For most people, flexing forwards, balancing, and exerting force through the pedals on a drop-bar bicycle compromises posture. This becomes taxing on our central nervous system and requires much more information to coordinate movements when compared to sitting upright on a Dutch-style bike would. Typically, when in a compromised position, our ability to stabilise and align our pelvis suffers.


The feedback from our feet plays a large part in how we align our pelvis in day-to-day life. If our feedback is asymmetrical our ability to align our body becomes skewed. Asymmetric vision, brain dominance, and proprioception will all impact how we perceive what straight feels like to us. The body has a large number of systems to corroborate with. Which is why people who are blind in one eye can still determine what straight is, they just rely on another feedback loop.


Without ensuring the CNS is functioning correctly we cannot expect symmetrical posture or force output. A large majority of people simply lack awareness of their body, how it’s positioned and how it’s adapted to their lifestyle. We’ve adapted to rely much less on our bodies functionality as we spend more time sitting down, driving, staring at screens, and moving a lot less. Most of our daily movements are somewhat repetitive and usually asymmetric.


As with any transfer of data - if there is a lot of “noise” and the information that needs to be transmitted isn’t getting through, the cerebellum will be unable to integrate the information into its calculations for the most efficient movements. Challenges such as posture, asymmetry and misalignment challenge the cerebellum and make it more difficult to send clear and efficient blueprints for movement patterns. The more challenges we can remove - the clearer and more efficient the movements patterns become.


Everything else is mere detail. When we help our clients achieve a well-functioning central nervous system, they find it much easier to optimise posture, alignment, and functional symmetry. Our fit decisions can help achieve this by focusing on the 3 key priorities of the CNS. After that, the rest is checking off the basics - making sure the cleat bolts aren’t protruding through the insoles, rotating the hoods and bars into a neutral position etc.

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