Recently ,in the process of comparing the Chimpanzee rearfoot to that of a human it occurred to me that of one of the ways in which the intrinsic foot muscles contribute to balance might be as follows
The question I asked myself was what type of balance system can take the apparently difficult to balance , tall ,top heavy ,human phenotype and use this shape to advantage ?

Well , first consider balancing a pencil on your finger . Its very difficult .
Easier to balance is a long broom handle due to inertia . Easier still is the act of balancing a complete broom on your finger /palm with the broom head in the air and the end of the broom on your hand .
So can the head of the tibia balance in this way on the talus/calcaneal unit ? I think the answer may be yes , at least for postural stability in the medio lateral direction .

Previously , Luke Kelly (1) has shown that the intrinsic foot muscles can control foot posture including the condition of the medial longitudinal arch and ,in my opinion ,this could lead to inversion and eversion of the calcaneus, and then via the talus ,to a movement of the tibal head relative to the COG .

Another paper has shown that the vestibular apparatus has a direct link to some of the intrinsic foot muscles showing the have a key role in balance . (2)

A third paper (3) indicates that in the absence of strong intrinsics the extrinsics seem take on more of role in postural stability an so enlarge .

So what I am saying overall is that the intrinsics handle small medio lateral perturbations via calcaneal positioning and with larger perturbations the extrinsics kick in to assist .

This theory places the intrinsics right at the very heart of human balance .

Any thoughts

Paper 1 Recruitment of the plantar intrinsic foot muscles with increasing ... Dec 2017 - Full-text (PDF) | The aim of this study was to determine the difference in activation patterns of the plantar intrinsic foot muscles during two quiet standing tasks with increasing postural difficulty. We hypothesised that activation of these muscles would increase with increasing postural demand...

Paper 2
vestibular modulation of the abductor hallucis and the ... - Scholars' Bank Thesis-Wallace.pdf?...1
by J Wallace - ‎2016 - ‎Related articles
explore the vestibular system. The purpose of this experiment was to determine if intrinsic foot muscles are modulated by vestibular activity and to elucidate any changes in the association between the vestibular stimulation and electromyography (EMG) responses in response to changes in head position, visual cues, and ...

Paper 3
Foot muscle morphology is related to center of pressure sway and ...
by X Zhang - ‎2017 - ‎Related articles
Gait Posture. 2017 Sep;57:52-56. doi: 10.1016/j.gaitpost.2017.05.027. Epub 2017 May 25. Foot muscle morphology is related to center of pressure sway and control mechanisms during single-leg standing. Zhang X(1), Schütte KH(2), Vanwanseele B(3). Author information: (1)Human Movement Biomechanics Research ...

Gerrard Farrell