Identifying Relevant Variables in Bike Fitting

One of the things I’m keen to do through my mentoring service is help people correctly identify the variables at play. It frustrates me when bike fitters fall back on “if X, then Y” thought processes that dumb down what we do and often result in poor outcomes for clients. If I see a client complaining of hand numbness or knee pain, I never just look at one thing – I want to explore everything that could cause that issue.

I have a lot of experience identifying variables in bike fitting, not just across my fitting career but also during my post-graduate study. When carrying out scientific research, the first thing you need to do is identify what changes could impact the thing that you’re studying. For example, when I was designing studies to look at ankle movement patterns in time trial cycling, these were a few of the variables I had to consider:

• Cleat position
• Saddle height
• Range of motion at the knee
• Intensity
• Cadence
• Range of motion at the ankle
• Whether participants run as part of their training
• Ability/race performance
• Learnt vs natural pedalling style
• Fitness levels/training intensity
• Recent positional changes
• Calf muscle strength
• Gender
• Shoe choice off the bike
• Relative strength of quads and glutes compared to calf muscles

This list definitely isn’t exhaustive, but it gives you an idea of how many things go into what appears to be a single, and simple, element of cycling. Some of these will be obvious to many of you reading this, but I want to run through them all quickly to make sure that it’s clear why I had to pay attention to each of them.

Cleat position: a more rearward cleat position requires less calf muscles activation to stabilise the ankle and resist the pedal reaction forces, while a more forward cleat position requires more muscle activation to achieve the same thing. Very forward cleat positions sometimes mean that the pedal reaction forces overpower the calf and result in more dorsiflexion (toe-up).

Saddle Height: if a participant’s saddle is too high then they may plantarflex (toe down) more than a rider with an optimal saddle height.

Range of motion at the knee: related to saddle height, in that if hamstring length is limited then the central nervous system often sends an inhibitory signal to contract the muscle slightly and resist further lengthening (in this case, resisting further knee extension). The only option for the rider to still get around the bottom of the pedal stroke is to point their toes down more.

Intensity: lower intensity means there’s less pedal reaction force to overcome, so it increases the likelihood of a stable ankle. An intensity above functional threshold power (FTP) – or what the rider usually experiences – might create more pedal reaction force than they’re used to and overpower the calf muscles.

Cadence: a faster cadence than the rider would usually select requires a completely different muscle firing pattern to the one they’ve trained over thousands, if not millions, of pedal strokes. So, with a higher cadence, you’re no longer looking at what the rider does naturally, but something untrained and unrepresentative instead. Riders who push a big gear with a low cadence will also experience higher pedal forces than a rider who spins, so a good study should try to account for this by having enough participants to compare the two groups.

Range of motion at the ankle: if significantly restricted, either by muscular range of motion or previous trauma within the joint, you might not see as much dorsiflexion as the average rider or you may not see the same muscle activation. Given that I was using EMG to identify muscle activation, this could have thrown out my findings hugely because the rider may have simply used the hard stop at the end range of motion to stabilise the ankle rather than muscular force.

Whether participants run as part of their training: running has been shown to increase Achilles tendon stiffness and could therefore change ankle movement patterns for triathletes and time trial cyclists that run, compared to time trial cyclists that don’t run.

Ability/race performance: high-end riders may select a different ankle movement pattern to lower-level or less experienced riders.

Learnt vs natural pedalling style: riders that have learnt to pull up on the pedals (this is bad btw, don’t do this!) often experience peak plantarflexion during the recovery phase of the pedal stroke. They are also more plantarflexed coming over the top of the pedal stroke than riders that don’t pull up, so their ankle movements through the power phase can often be very different to riders that don’t pull up. The same is true of riders that pull backwards through the bottom of the pedal stroke (also not great), who tend to plantarflex more to try and use their feet like swimmers use their hands to catch the water during front crawl.

Fitness levels/training intensity: if the participants are too far away from race fitness, their pedal strokes may vary slightly compared to when fully fit. If they participate in the study too soon after an intense training session, then the fatigue induced by a hard session could also change how they pedal.

Recent positional changes: some elements of positional adjustments can take time for the body to adapt to. Cleat position is a good example of an adjustment that takes several weeks for the body to identify an optimal pedalling style for the new set of parameters.

Calf muscle strength: weaker calves are more easily over-powered by pedal reaction forces.

Gender: gender differences in Achilles tendon characteristics are significant, with men having ~29% stiffer tendons (Kubo et al 2003), even when adjusted for body size and muscle strength.

Shoe choice off the bike: people who regularly wear shoes with a significant heel to toe drop – think high heels, but also men’s dress shoes with a lift – can experience a reduced dorsiflexion range of motion at the ankle. This is the result of spending a lot of time in plantarflexion, and, as the old phrase goes, if you don’t use your dorsiflexion RoM then you’ll lose it.

Relative strength of quads and glutes compared to calf muscles: this one goes without saying but is often overlooked in cycling. If the glutes and quads produce most of the force going into the pedal, then the ankle plantar flexor muscles (calves) need to be strong enough to resist the pedal reaction forces they create. So, huge glutes and quads create huge pedal reaction forces, which requires stronger calves than smaller glutes and quads.

My study attempted to control for several of these variables by excluding certain participants and identifying tendon stiffness and calf strength. If you’re interested, I did this by looking at tendon excursion using an ultrasound scanner with the tendon under load while conducting strength tests on a dynamometer. All very nerdy, but a super interesting way of exploring why we pedal like we do and attempting to fill in another piece of the puzzle.

If you can think of any other variables that could impact how someone moves their ankle, I’d love to hear them. As I said, this list isn’t exhaustive so there’s still a few missing.

If you’re interested in talking about things like this in more detail, and would like to learn how these concepts can be applied more broadly to bike fitting, sign up for my mentoring programme.