Overpronation is one of the most frequently used terms I hear in fitness. This is from both trainers and clients. The plethora of pronation control shoes has plucked the word from the world of anatomy and physiology and biomechanics into everyday terminology.
Although the word is widely used it is not widely understood. Overpronation can happen in many ways and for multiple reasons but is generally used as a generic term and no more attention is paid to it.
Lets first define pronation. It is the triplane action of dorsiflexion, eversion and abduction at the rearfoot. These joint motions are relative to the bone motion of the talus which is the primary moving bone in a closed chain scenario. This rearfoot motion will also create relative forefoot dorsiflexion, inversion and abduction. The forefoot can have quite an impact on rearfoot pronation that we will talk about later in the blog!
Now lets look at the different ways in which we can overpronate.
1. Range-I think this is the "classic" definition of overpronation. The amount of distance that the joint goes through. Obviously far too much range places stress on the joint and muscles all through the kinetic chain of the lower limb. The associated tissues have to work hard to control the excess range. Common problems that can arise are posterior tibialis syndromes, Achilles problems and ITB problems.
2. Rate-Along with range goes the rate or speed/acceleration of pronation. The larger the range, the more distance to accelerate into. This again causes problems for the muscles/tissues that have to decelerate this increased acceleration.
3.Sequence-This is the most overlooked element of overpronation. Pronation should occur at initial heel strike and be followed by supination. If the range and rate are excessive then the foot is unable to reverse the motion in time to go into supination. This means that someone may pronate through midstance and also through the propulsive phase of gait. If any of the motions associated with supination are restricted it may also lead to a return to pronation late in the gait sequence.This can also be because of the instability created by the pathomechanics of different foot types. This can lead to plantar fascia problems and HAV bunions as the foot remains in its unlocked mobile state rather than becoming the rigid propulsive unit that the supination process creates.
The question most often overlooked when it comes to pronation problems is WHY?? A good knowledge of foot dysfunction is required to really answer this question. The most overlooked area in my opinion that causes pronation problems is ontogenic (developmental) forefoot positioning relative to the rearfoot. However I am also really interested in the spatial location of the STJ (subtalar joint) axis. The medial deviation of the STJ will increase the moment arm of GRF (ground reaction forces) associated with pronation and decrease the moment arm of the supinatory muscles. It will also increase the area of the foot laterally to the STJ that cause pronation to happen when force is applied. The lateral deviation will do the opposite with more internal muscular supinatory force and decreased GRF pronatory force occurring and increased medial area of the foot that will cause supination.
Anyway, back to the forefoot!! An inverted or varused forefoot position will be compensated for at the rearfoot by excess pronation. Another scenario is that the foot is able to get into supination but the extra instability of the varused forefoot causes a pronation response to get the forefoot on the ground and create stability. This would happen late and out of sequence in the gait cycle. This means that just controlling the longitudinal arch as many pronation control shoes do, does not gain quite the control anticipated.
Many times I also see short or half foot orthotics. These orthoses have arch control but do not provide stability at the forefoot. This is done by bringing the ground up to the foot, to stop the foot trying to search out the ground. Without the forefoot control I see the foot unable to pronate to compensate because of the arch control, instead using the transverse plane to rotate the foot and tip onto the forefoot. This maybe a reason behind a medial heel whip!! A similar thing can happen when the STJ axis height is high and favours transverse plane motion over frontal. The STJ axis height should be around 42 degrees from the transverse plane, slightly favouring frontal plane motion.
I realise this a bit of a big post, but is also a really big subject. Much more complicated than many give it credit for, so thanks for reading. Until next time....