Getting to grips with the central nervous system

IBFI Mentoring

The central nervous system is critical to how we move and function, which means understanding the way it operates is critical to successful bike fitting. IBFI mentee Jon Gatiss-Wild from Bristol, UK, explains.

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

How we move

All coordinated human movement starts with the intention to move from the motor cortex. The motor cortex notifies the cerebellum at the base of the brain of its intent to initiate movement. At the same time, the cerebellum is being 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.

Prioritising functions

In any athletic activity, the CNS has three fundamental priorities:

1. Breathing

There are three energy pathways which fuel human movement. The body can only produce 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 body’s survival. 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

Secondary to breathing, posture can be thought of as 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 above, 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 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.

Fitting for on the body's priorities

Every measure taken or intervention made during a bike fit must be considered in relation to these three priorities and the way they are ordered, and 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 body’s 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.

System efficiencies

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.

Foot feedback

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 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.

Cutting through the noise

As with any transfer of data - if there is a lot of noise and the information that needs to be ‘ The more challenges we remove, the clearer and more efficient movements become 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 and everything else is mere detail.

Optimising fit decisions

When we help our clients achieve a well-functioning CNS, they find it much easier to optimise posture, alignment, and functional symmetry. Our fit decisions can help achieve this by focusing on the three 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, and rotating the hoods and bars into a neutral position.

Jon worked with Australian IBFI level four bike fitter Steve Hogg, to analyse the importance of the central nervous system in bike fitting. If you’re a level 1 or 2 fitter and you’d like to take part in the IBFI’s free mentoring programme, or if you’re a level 4 fitter and would like to be a mentor, email Tom at mentoring@ibfi-certification.com