Tom Purvis hits some strong points in this video about squatting, hip hinges, ankle dorsiflexion, and movement as a whole.  * Keep in mind, this is all sagittal plane stuff….. it gets far more complicated when there are lateral (frontal) plane or rotational (axial) considerations ….. these are the “knees out” dialogues and debates you have read over and over on the web in the last year.

Dr. Shawn Allen

addendum:

Food for thought after posting today’s Tom Purvis squat video.

Could this study below translate into the statement/question: 

“attempting to achieve sufficient dorsiflexion through the combined ‘foot pronation-ankle dorsiflexion’ mechanism, as opposed to just dorsiflexion from the ankle mortise joint alone, may change the dynamics of the entire limb…. in this case, hip flexion range observation. Is this because when dorsiflexion is cheated via foot pronation, instead of just ankle dorsiflexion, there is more internal tibia/femoral spin than would normally occur from just sagittal ankle hinging which can in turn impair terminal hip flexion range via impingement type action ? I think so. It would be cool to see what would have happened in the study had the pronating clients been shown my foot tripod restoration exercise (it’s on youtube).   -Dr. Allen

here is some new research on this point, for what it is worth.  It keeps the mind thinking though.

J Phys Ther Sci.  2015 Jan;27(1):285-7. doi: 10.1589/jpts.27.285. Epub 2015 Jan 9.The kinematics of the lower leg in the sagittal plane during downward squatting in persons with pronated feet.  Lee,Koh da,  Kim 

Abstract

[Purpose] This study aimed to examine changes in lower extremity kinematics in the sagittal plane during downward squatting by subjects with pronated feet. [Subjects and Methods] This study selected 10 subjects each with normal and pronated feet using a navicular drop test. The subjects performed downward squatting, in which the knee joints flex 90° in a standing position. We recorded the angles of the hip, knee, and ankle joint in the sagittal plane through motion analysis. For the analysis, the squatting phase was divided into phase 1 (initial squat), phase 2 (middle squat), and phase 3 (terminal squat) according to the timing of downward squatting. [Results] In the pronated foot group comparison with the normal group, thehip joint flexion angle decreased significantly in phases 2 and 3. The dorsiflexion angle of the ankle joint increased significantly in phase 3. The flexion angle of the knee joint did not differ between groups in any of the phases. [Conclusion] The pronated foot group utilized a different squat movement strategy from that of the normal foot group in the sagittal plane.

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