Broom balance strategy, part of the balance system

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• Back in 2017 I suggest here on podiatry arena , that to some degree, human balance, in single leg stance, was controlled via a "broom balancing act" with the intrinsic foot muscles as the main method of control for this aspect . I don't know if the idea had been floated before but given recent research it seems increasingly likely to be correct.
  Extract " Intrinsic foot muscles .The heart of balance ? Jan 2018 Biomch-l
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• 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 tibial 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 ?
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• From Kelly et al . The intrinsic foot muscles can control the position of the base of the tibia and help control balance ( note middle diagram)
  
  Paper 1 Recruitment of the plantar intrinsic foot muscles with increasing ...
  
  https://www.researchgate.net/.../515...nsic_foot...22 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
  
  https://scholarsbank.uoregon.edu/xmlui/bitstream/.../Final 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 ...
  
  Foot muscle morphology is related to center of pressure sway and control mechanisms during single-leg standing - PubMed
  https://www.ncbi.nlm.nih.gov/pubmed/28575753
  Maintaining balance is vitally important in everyday life. Investigating the effects of individual foot muscle morphology on balance may provide insights into neuromuscular balance control mechanisms. This study aimed to examine the correlation between the morphology of foot muscles and balance perf …
  
  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 ...
  
  

 

In 2011 Kelly et al published a paper titled- Recruitment of the plantar intrinsic foot muscles with increasing postural demand. Here is the conclusion of that paper -
Interpretations

Activation of the plantar intrinsic foot muscles increases with increasing postural demand. These muscles are clearly important in postural control and are recruited in a highly co-ordinated manner to stabilise the foot and maintain balance in the medio-lateral direction, particularly during single leg stance.

This is an insightful piece of work.

I have no idea if Kelly had the "upside down broom in the palm of your hand " model of balance in his mind when he wrote the paper but it fits very well with the papers findings.

Now added to Kelly is a paper from Trotman et al concerning the "..vestibular control of balance in the intrinsic foot muscles" . This paper found-
"Our findings demonstrate that whole-body vestibular-evoked balance responses were adjusted in response to altered mediolateral stability and head posture, in part, via modification of intrinsic foot muscle activity."

So it may well be that the findings of Kelly 2011, intrinsic muscle involvement in medio lateral balance, is a mechanism controlled directly by the vestibular apparatus of the inner ear and that , IMO , balance is via the broom type mechanism .

The base ( I called it the head in previous posts and this was an error) of the tibia sits on the talus which in turn sits on the calcaneus . The intrinsic foot muscles, and, based on Trotman, the abductor hallucis and abductor digiti minimi in particular, can alter the orientation of the talus/calcaneus and hence the orientation of the tibia itself.

To maintain balance then the human body employs a number of strategies with the vestibular/ intrinsic foot muscle broom balance strategy being a key component esp in fine balance adjustments in single leg stance . Note that something close single leg stance could be present when leaning in one direction to pick something of a shelf etc



Luke A. KellySami KuitunenSebastien RacinaisAndrew G. Cresswella.cresswell@uq.edu.au
Abstract

Background

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 and be correlated with postural sway.
Methods

Intra-muscular electromyographic (EMG) activity was recorded from abductor hallucis, flexor digitorum brevis and quadratus plantae in 10 healthy participants while performing two balance tasks of graded difficulty (double leg stance and single leg stance). These two standing postures were used to appraise any relationship between postural sway and intrinsic foot muscle activity.
Findings

Single leg stance compared to double leg stance resulted in greater mean centre of pressure speed (0.24ms−1 versus 0.06ms−1, respectively, P≤0.05) and greater mean EMG amplitude for abductor hallucis (P≥0.001, ES=0.83), flexor digitorum brevis (P≤0.001, ES=0.79) and quadratus plantae (P≤0.05, ES=0.4). EMG amplitude waveforms for all muscles were moderate to strongly correlated to centre of pressure (CoP) medio-lateral waveforms (all r≥0.4), with muscle activity amplitude increasing with medial deviations of the CoP. Intra-muscular EMG waveforms were all strongly correlated with each other (all r≥0.85).
Interpretations

Activation of the plantar intrinsic foot muscles increases with increasing postural demand. These muscles are clearly important in postural control and are recruited in a highly co-ordinated manner to stabilise the foot and maintain balance in the medio-lateral direction, particularly during single leg stance.