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BikeDynamics - Bike Fitting Specialists

Bike Fitting Guidelines - Foot to Pedal

Frequently ignored compared to the saddle, the foot-shoe-pedal interface is critical to enjoying a powerful and comfortable riding position. Manufacturers are well aware of this and strive to provide stiff-soled shoes and rigid pedal platforms to maximise energy transfer from muscles to forward motion. The efficiency in this mechanism is dependent upon minimising wasted motion and by ensuring the numerous bones and muscles in each foot remain firmly planted and stable. As the foot is stable so the knee and hip alignment remains stable.

The key factors controlling foot stability are as follows:-

 

Fore-Foot Varus or Valgus angle

varus and valgus forefoot and rearfoot
From "Understanding Joints" by Bernard Kingston

When standing or walking, both the heel and forefoot are utilised. When riding, most sensible people apply forces to the pedals through the fore-foot. The angle of the fore-foot with respect to the lower leg is called either varus (big toe up) or valgus (big toe down). Given the forces applied via the fore-foot to a flat insole / pedal platform, one could imagine how a large valgus or varus angle will result in the application of a moment to the lower leg, manifesting as a lateral displacement of the knee as the load varies around the pedal stroke. Cyclists will often let their knees wobble in and out or apply muscle forces to steady the motion. Either way is inefficient.

One means to correct this error state is to place a stiff wedge in either the insole or between the cleat and shoe plate. Specialized have a range of shoes (Body Geometry) that have a 1.5 degree varus tilt built in to the sole. Internal and external wedges are also available commercially. At BikeDynamics we can measure the fore-foot angles and in conjunction with dynamic assessment recommend the angle and direction of wedges that should suit you best.

 

Foot Rotation (toe in or toe out)

Establish your foot angle by observing them whilst walking, standing up straight and dangling your feet over the side of a table. There will be differences between the three but the fundamental toe in or out should be apparent. If in doubt you will need to use a measurement device such as the Keo Fit System. Replicate this angle by flipping the shoe over and matching the angle in the opposite direction. The cleat should point straight ahead.

This will have a nominal position and be coupled with hip, ankle and knee joint movement. In fact, the foot is often regarded as a dial indicator for the automatic (i.e. involuntary) rotations of the lower limb. Rotation during the pedal stroke is normally accommodated by the amount of float between cleats and pedals. This is fine provided the maximum rotation does not exceed the total float, and more importantly that the cleat accommodates the nominal position and does not 'bottom out' during the pedal stroke. The angular rotation of the foot may also define the lateral spacing of the cleats. Cycling publications often talk of Q angles when discussing pedal to pedal spacing (Q actually stands for quadriceps angle and is related to the angle formed between the shafts of the femur and tibia). As most of us ride on bikes with standard bottom brackets and components, we don't have very much adjustability here other than a small amount within the cleat. For those of us with excessive toe out we need to use this (and even additional washers or pedal spacers) to prevent heel strike against the crank arms.

 

Cleat Longitudinal Location

The above diagram (from "Understanding Joints" by Bernard Kingston) shows a diagram of the many bones of the foot. The "ball" is regarded as the area at the distal end of the five metatarsal bones. For cycling we need to use a horizontal line, so choose a best fit through the first three. In the diagram shown, the horizontal alignment of the three is very good but in the real world this is not always the case, the second often being the longest. The position of the first metatarsal is fairly easy, being the bony bump on the side of the foot by the big toe. The second and third often reveal themselves when the toes are flexed.

The recommended foot position over the pedal spindle is almost universally acknowledged as the ball of the foot. The ball is one of the three "rockers" of the foot, along with the heel and big toe. It is at the end of the body's only first-class lever, and is ideally placed to be both a powerful and stable point to apply pressure to the pedal. The "ball" could be regarded as quite a large area though, so we need to be a little more precise in defining exactly what we mean by it.

Incorrect placement of the foot over the spindle will tend to separate the applied centre of pressure (foot to shoe) from the reactive force at the pedal spindle. The resultant couple will tend to create unwanted "ankling" unless restorative muscle energy is used to keep the foot stable. Of course, many cyclists intentionally "ankle" to make best use of that first-class lever to give more motive power, but this makes no difference to the recommended foot position.

 

Pronation or Supination and Arch Support

Knee tracking

The effects of either over-pronation or over-supination during walking and running are reasonably well understood. This is where foot posture causes the load path from heelstrike to toe-off to take either an inward (pronation) or outward (supination) route. This is associated with flat-footedness or high arches respectively. The implications to cycling are less clear as peak forces are lower and always applied to the fore foot. A potentially poor scenario is to have high arches that collapse under the applied loads. This would result in a fluctuating lateral knee movement similar to that due to high forefoot varus angles.

Fortunately cycling shoe manufacturers now recognise this and offer insoles with varying levels of arch support. See the measurement page to see how we can measure foot type using a Footdisc. BikeDynamics has a stock of insoles in all the usual sizes to evaluate during the fitting process.

 

Coupling of Ankle Dorsiflexion with Foot Inversion

Graph plotting ankle and knee angles against crank displacement

Plot showing correlation of ankle angle to knee lateral displacement over 4 complete cycles. As the ankle angle reduces (dorsiflexion - left hand scale) the knee moves towards the frame (right hand scale).



Many people show a strong coupling between the angle of their ankle (between foot and tibia) and the inversion or eversion of the foot. This tends to be seen as an outward rotation of the foot (inversion or big toe up) as the angle tightens (dorsiflexion). Some people also show high levels of dorsiflexion as the leg comes over the top of the powerstoke and load is applied. This has a very similar characteristic to a varus forefoot in that the knee will sway in towards the frame. One countermeasure here is to stiffen the ankle or even push down with the toe (plantarflexion) to prevent the ankle angle tightening. Frequently, this dorsiflexion is a result of a lack of arch support. As the arch drops, the plantar fascia (connective tissue between heel and toes) effectively lengthens, allowing the toes to lift relative to the ankle.




 

BikeDynamics Bibliography

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If you are going to buy one book on Bike Fitting and the implications to injury, comfort and performance - this is the one.

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The latest scientific knowledge in a range of subjects from Biomechanics to Nutrition.

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There is no excuse for not doing enough stretching!

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Good anatomical summary but also very strong on suitable weight training workouts.

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'The' text book on conditioning, road cycling biomechanics, nutrition, hydration and trauma.

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A practical guide to the human body without being too "clinical".

 

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Everything you need to do well in Cyclosportives.

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Great little book, just need to start ticking them off.

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Ideally it would be a bit longer, but good enough!

 

 

 


Page Last Updated : 10th February 2013 All Rights Reserved. BikeDynamics - Bike Fitting Specialists