Pronation Primer: Part 1
A lot of folks seem to be on a mission to eliminate pronation, calling it the scourge of humanity and source of human ailment. While we agree that overpronation causes biomechanical faults in the lower kinetic chain, so does under pronation, and some pronation is necessary and required for normal locomotion. We hope this post serves to clarify any misconceptions there may be about it.
When most people think of pronation, they think of midfoot pronation, or pronation about the subtalar or transverse tarsal joints. Pronation can actually occur about any articulation or bone, but with respect to the foot, we like to think of rearfoot (ie. talo-calcaneal), midfoot (talo-navicular) and forefoot (transverse tarsal). The question is why does this matter?
Pronation, with respect to the foot, is defined as a combination of eversion, abduction and dorsiflexion (see picture attached) which results in flattening of the planter vault encompassing the medial and lateral longitudinal arches. In a normal gait cycle, this begins at initial contact (heel strike) and terminates at midstance, lasting no more than 25% of the gait cycle.
In a perfect biomechanical world, shortly following initial contact with the ground, the calcaneus should evert 4-8 degrees, largely because the body of the calcaneus is lateral to the longitudinal axis of the tibia. This results in plantar flexion, adduction and eversion of the talus on the calcaneus, as it slides anteriorly. At this point, there should be dorsiflexion of the transverse tarsal (calcaneo-cuboid and talo-navicular joints). Due to the tight fit of the ankle mortise and its unique shape, the tibial rotates internally (medially). This translates up the kinetic chain and causes internal rotation of the femur, which causes subsequent nutation of the pelvis and extension of the lumbar spine. (Hmm, this is beginning to sound like a common cause of low back pain) This should occur in the lower kinetic chain through the 1st half of stance phase. The sequence should reverse after the midpoint of midstance, causing supination and creating a rigid lever for forward propulsion.
Pronation, along with knee and hip flexion, allow for shock absorption during throughout the 1st half of stance phase. Pronation allows for the calcaneo-cuboid and talo-navicular joint axes to be parallel making the foot into a mobile adaptor so it can contour to irregular surfaces, like our hunter gatherer forefathers used to walk on before we paved the planet. Problems arise when the foot either under pronates (7 degrees valgus results in internal tibial rotation), resulting in poor shock absorption or over pronates (> 8 degrees or remains in pronation for greater than 50% of stance phase).
Wow, kind of overwhelming, eh? Stay tuned for part 2 tomorrow.
We remain….The Gait Guys…Telling it like it is…..