Originally Posted by Th3g1ng3r1
I thought I'd ask my question in this thread rather than start a new one. I am a former GB track cyclist that has just completed a BSc sports Rehabilitation degree at Middlesex University in the UK. Now that I'm back in the real world, I am looking to do some work with bike fit combined with corrective exercise for injury treatment and prevention. I have been reading with interest all of the cycling related threads on this forum and related journals but I have a question regarding the rationale behind cleat wedges and forefoot insole wedges. Obviously my degree only skimmed the surface of knowledge on the foot so please forgive me if I am asking a stupid question.
As I understand it, a forefoot varus causes the STJ to pronate during the power stroke and therefore the knee to move medially. Therefore, I can understand that putting a forefoot valgus wedge under the insole would support the forefoot and not let it collapse and maintain the STJ in relative neutral. However, wouldn't a valgus wedge under the cleat affect the angle of the entire sole of the shoe? While reducing the collapse of the forefoot, wouldn't in also move the STJ into a degree of supination?
I humbly bow to your superior knowledge in these matters.
Both Eric and Simon have given good advice so far. I have been treating cyclists for the past 25 years and have been involved in a few bicycle related biomechanical studies, with one study being published that showed a correlation of subtalar joint axis location to knee joint loads (Ruby P, Hull ML, Kirby KA, Jenkins DW: The effect of lower-limb anatomy on knee loads during seated cycling. J Biomech, 25 (10): 1195-1207, 1992).
My treatment goals during cycling is 1) prevent abnormal forces which may be causing symptoms during cycling and 2) to make the subtalar joint, midtarsal joint and midfoot joints as stiff as possible while still allowing normal ankle joint motion and in order to improve the mechanical efficiency of force transfer from the lower extremity muscles to the metatarsal heads of the foot. These goals guide my treatment of all cyclists.
There are few ways that I manipulate the foot-pedal mechanical interface in order to improve the mechanical efficiency of the cyclist. I may often add lifts between the shoe sole and the cleat in order to equalize limb length differences or will add varus or valgus wedges between the shoe and cleat for frontal plane abnormalities.
Foot orthoses also work well in cycling shoes for those feet that are relatively compliant in the medial arch and demonstrate subtalar joint pronation/medial knee translation toward top tube during the power phase of cycling. If the subtalar joint pronates during the power phase, the knee will move medially toward the top tube in a kind of elliptical pattern (when viewed from in front of the cyclist). By using foot orthoses to increase the stiffness of the foot during the power phase, more "straight up and down" knee kinematics is produced and more efficient force transfer to the pedal is created during cycling.
I may also use in-shoe forefoot wedging such as reverse-Morton's extensions (a type of forefoot valgus wedge) along with varus cleat wedging to not only invert the shoe to the pedal but also evert the forefoot to the shoe in order to stiffen the midtarsal-midfoot complex and further improve the force transfer to the pedal during the power phase. I have also seen some cyclists show a paradoxical supination of the foot with addition of valgus forefoot wedges to the shoe
which I have hypothesized is caused by the central nervous system of the cyclist "sensing" that the more supinated position of the foot on the pedal with a valgus forefoot wedge is the most comfortable or metabolically efficient way to transfer force to the pedal during cycling.
Very interesting stuff, this cycling biomechanics. Unfortunately, it is rare to find a podiatrist that knows very much about cycling biomechanics and treating cyclists since this is not normally covered in podiatry school courses.
Hope this helps.
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
107 Scripps Drive, Suite 200
Sacramento, CA 95825 USA
Voice: (916) 925-8111 Fax: (916) 925-8136