Sitting Pretty DIY Bike Fit Part 4: Foot Correction
Foot Correction is the term I use to describe the process of ensuring that proprioceptive feedback from the feet is prioritised by the cerebellum for processing. Before continuing I had best explain what that means, as it has significant implications for cycling performance and injury reduction. Bear with me as the explanation is lengthy and I know that many readers who ‘just want to ride my bike’ may find it eye glazing. Persevere though, as it is necessary if you are to understand the importance of what follows for your performance.
When we perform any sequence of actions, like walking across a room or riding a bike, it is usually a conscious thought that triggers what follows. What is unconscious is the muscle firing sequence (motor pattern) that allows the coordinated actions for the task. No one pedals a bike thinking ‘I’m going to activate Muscle X and relax Muscle Y’; we just ride. The part of the brain that plays the major part in determining the muscle firing sequence is called the cerebellum. Proprioception is the name given to the cerebellum’s awareness of what the body is doing in space.
It gains that awareness from the output of hundreds of millions of sensory nerves named proprioceptors that are distributed throughout the body. These are not distributed evenly; 50% of them are in and around the upper and lower jaw. Another 25–30% are located in and around the two sacroiliac joints where the lower spine butts up against the pelvis on each side. The remaining 20–25% are in every bone, muscle, ligament, tendon and joint. Between them they convey a constant flow of information; something like three-billion signals per second to the cerebellum informing it of the load each body part is experiencing, where each body part is in space and how each body part relates to gravity. So every second, 3,000,000,000 signals are generated by the body and all arrive at the cerebellum which has a maximum processing capacity of 2,000 signals per second. This means that the cerebellum can only process something like 0.00005% of the total proprioceptive feedback it receives. Another way to frame this is that the cerebellum can only process one proprioceptive signal out of every 1.5 million that it receives.
When I first read those numbers, my initial thought was that there had to be a hierarchy of priorities dictated by evolution as to what the cerebellum chooses to prioritise for processing and what it chooses to ignore. And if that hierarchy could be determined, there was potential for increased cycling performance as well as a decreased risk of incurring overuse injuries from cycling, through optimal neuromuscular coordination. Crashes aside, all cycling injuries are overuse injuries.
To analogise, think of yourself and a friend being in the crowd at a sporting match. The two of you are intent upon a conversation with each other and are focused on that conversation. Even so, you are still aware in a background sense of the noise made by 150,000 murmuring spectators; you’re just not paying attention. Multiply that situation by an order of magnitude and you get a glimpse of the situation of the cerebellum.
The cerebellum will always prioritise two classes of stimuli for processing. The first is the generation of force, because in an evolutionary sense, this has clear survival value. By that I mean that if you are running for your life or fighting for your life, you are literally betting your life that you will coordinate those activities as well as is humanly possible as like every other organism on the planet, your fundamental priority is survival. Everything else is secondary.
Within this category of force generation, we automatically allot a higher priority to force exerted anywhere below the top of the pelvis than we do force exerted anywhere above the top of the pelvis. Again an evolutionary imperative is at work.
We have evolved to be upright creatures who primarily contact planet Earth through our feet. From the top of the pelvis down is our postural foundation. In turn that means that given the disparity between proprioceptive signal reception by the cerebellum and its ability to process only a tiny fraction of that signal traffic, there is no evolutionary mileage in only being able to use your arms, bend your torso or nod your head, if at the same time you are forced to collapse at the hips, knees or ankles. So the lower body gets first priority; the upper body gets second priority for processing in matters of force exertion.
The second category of stimulus that will always be prioritised by the cerebellum is any changes in the quality of feedback from any area of the body. A metaphorical whisper that is being ignored can quickly be elevated in to a metaphorical shout that is being processed if there is sufficient change. A simple example is that if someone tugs on your cycling jersey, you become more aware of the part of the body that felt that tug than you were previously. The increased awareness only lasts a few seconds before your unconscious attention drifts off on to other matters as it always does.
The key thing to understand about what follows is that nobody has a clear proprioceptive awareness of the feet while cycling. This can be demonstrated and I do so daily with clients. I won’t explain the procedure now because the testing regime forms part of a patent application that has been granted in the UK, USA and New Zealand but is ongoing in Australia. In the near future I will be able to be more frank.
I mentioned in Part 2 of this series that any ‘challenge’ to a rider’s position in space will evoke an immediate and unconscious compensatory response and that all compensatory responses tend to increase the disparity between how the left and right sides of the body function. Given that a bike is a symmetrical apparatus in a positional sense a high degree of functional symmetry is desirable for best performance and lowest chance of injury.
Lack of proprioceptive clarity from the part of the body that you use to transfer the power you produce to the pedals, the feet, is a ‘challenge’ (with consequent increase in asymmetric function) that every rider faces. So for optimal performance we need to have the proprioceptive output from the feet prioritised for processing by the cerebellum at all times while cycling.
THE NEED FOR ARCH SUPPORT
This all comes down to the alignment of the feet. Optimal alignment is achieved by a combination of arch support and when necessary, as it often is, further canting of the feet. Of the two things, arch support is fundamental for the following reason.
When we fire the muscles of the leg while cycling, walking or running, the cerebellum oversees the task but does not directly control it. The basic pattern of ‘extensors on / flexors off’ on the pedal down stroke and ‘flexors on / extensors off’ on the pedal upstroke is controlled by a bundle of neurons in the lumbar spine called the central pattern generator (or CPG). The CPG relies on force feedback from the feet for its informational input, of which a primary component is plantar fascia tension (the plantar fascia is under the arch of each foot and connects the MTP joints—the base knuckles of the toes—to the rear of the foot).
When we walk and run, activities that we have evolved to do, the foot changes shape constantly and plantar fascia tension also changes constantly as a consequence. This constant change in tension stands out from the background ‘chatter’ engulfing the cerebellum and is given priority for processing.
In contrast we have not evolved to cycle and while exerting force on a rigid cycling shoe sole, for most people, plantar fascia tension changes little if at all. Because of the largely unvarying quality to the proprioceptive output of the plantar fascia while cycling, the central nervous system tends to ignore the feedback from that area and not prioritise it for processing.
The better the informational input to the CPG the better and more accurately it will control the muscle firing sequence that allows us to propel the bike and the more symmetrically the rider will relate to their bike. So we need to create some tension in the plantar fascia.
On a three level scale of Not Intrusive, Mildly Intrusive and Very Intrusive, arch support inserts for cycling need to be Level 2 (Mildly Intrusive). The simplest way to determine this is that when off the bike and standing in cycling shoes, the degree of intrusiveness of arch supports should not feel painful, but should certainly feel like one level higher than would be comfortable in a walking shoe. Once you get back on the bike and ride for five to 10 minutes you should not be consciously aware of the arch support unless you focus particularly on it. There should be no discomfort while cycling.
Sadly, it is rare rider who will achieve this desirable Level 2 degree of arch support because most cycling shoe insoles are a bit of an afterthought. Some manufacturers like Shimano, Fizik and Specialized have standard insoles or options that are much better than most, but even then, the highest level of arch support they make available is too low for most riders.
The easiest to use and most adaptable option available is the aftermarket G8 Arch Tech 2600s which are packaged with five different arch height inserts that can be adjusted forward / back and in /out in seconds for best individual result. If you try the G8s or anything similar, the arch insert height doesn’t have to be the same on each side. What you are trying to achieve is the same feeling of ‘mildly intrusive when standing’ on both sides. For most, this will be the same height on each side. For some it will not.
WEDGING OF THE FEET
Once there is enough tension created in the plantar fascia, fine tuning is necessary. This is where wedging comes in. Wedges are available in three forms; in-shoe wedges, cleat wedges and heel wedges. In-shoe wedges have a direct effect on the forefoot, but because they are placed underneath a shoe insole and over the point of contact with the pedal, they also have an indirect effect on the rear foot. Cleat wedges are placed between the cleat and the sole of the shoe and cant the entire foot. Overall they have the same effect as an in-shoe wedge. Heel wedges fit underneath the heel of the shoe insole and affect only the rear foot. Both cleat and heel wedges have a one degree taper.
Which to Use?
In-shoe wedges take up a lot of vertical space in the toe and more than one is impractical for most riders over the long-term because they compromise foot comfort. What they are best for is as a bike fitting diagnostic tool because they can quickly be added to or removed from a shoe without need for tools.
Cleat wedges perform the same function as in-shoe wedges and because they are placed underneath the cleat, they don’t compromise shoe fit.
Heel wedges have their place; in fact 70% of people need a heel wedge or wedges, either alone or in combination with cleat wedges.
The key to ensuring proprioceptive clarity is firstly, the correct degree of arch support inside the shoe and secondly, the correct amount and location of wedging. While I have a method to determine what is required based on quantifying the proprioceptive response from the feet, until the patent application is granted, I can’t talk about it publicly. Still there is a relatively simple way to determine ideal wedging numbers or very close to it. It time consuming but well worth the effort and is outlined below.
The Dustin Dumbbell Method
Below is an edited cut and paste of correspondence I’ve had with Dustin, a US rider from Texas.
“After fitting level two arch support as you suggested, I have been all over the place with different combos of heel and cleat wedging until September, when I put my bike in a trainer and tried lifting a 15-pound dumbbell in front of me one side at a time with arm at full extension (being careful not to destroy my brake hoods) trialling every combo of heel and cleat wedges between zero and three wedges in total. I found that on each side I could lift the weight eight or nine times with every combo but one, which allowed me to lift the weight 14 times. This happened to be one cleat wedge on the right and one cleat wedge and one heel wedge on the left. With this combination I immediately felt better and stronger on the bike. My knees are tracking straight, my right foot no longer feels unstable and slippery on the pedal, and both feet are uniform (as opposed to left heel out, right heel in). I went from having significant medial right knee pain after a 50-mile ride one week, to riding 75 miles with 1,500ft elevation gain the next week (I live in a flat area and my largest elevation gain prior to that was around 50ft), and 180 miles in two days the week after that without knee pain.
What Dustin has done is clever and I’ll explain why it worked so well. He has fitted his bike to a trainer and pedalled under load (exerting force with the lower body ie highest priority task from a motor control point of view) while at the same time lifting a dumbbell with each arm in turn at full extension of the arm (ie exerting force with his upper body which is a lower priority motor control task). The reason that he could complete more repetitions of the dumbbell lift on each side one his foot wedging was optimal is as follows.
Because we don’t have optimal proprioceptive awareness of what the feet are doing while applying load to the pedals, the cerebellum is using a proportion of its capacity constantly chasing information about the task and not getting it. That wasted capacity is not available for lifting the dumbbells because lower body effort, pedalling; is higher priority than upper body effort; lifting the dumbbell with each arm.
Once Dustin had found the optimal degree and placement of wedging for each foot, the wasted capacity is made available for any other task at hand, which in this case was lifting the dumbbells.
I encourage you to give Dustin’s method a try. Dustin used up to a maximum of three wedges in his testing. While not unknown, it is an uncommon rider who needs more than three wedges on one side with the average per rider being a total of between two and three for both feet combined.
Next issue I’ll deal with setting seat height and seat setback.