Episode 5

The last segment in the quest to fix our feet navigated through caverns and arches of foot bridges.  

We find ourselves now at the apex of the main bridge of the Foot Pain Trail.

Here we find two intersecting arcs, and an engineering marvel.

Getting our bearings:

The bridge we are on (the medial longitudinal arch, or MLA) leads on to the heel bone. 

Perpendicular to where we stand, observe an arc of interest in this natural system …

This episode illustrates the mechanism of the arches.  

The fun of the trail is the mystery of where it leads:

While I was a student in Kingston Ontario, a yellow tipped, orange triangle caught my eye.

Then another one, and another – enticing me where?

They led me out of the city onto an increasingly bucolic footpath.

Meters became kilometers, and minutes morphed into hours.

Ten and a half kilometers later I gave up.  There was still no end in sight to the distinctive trail markers. 

Ten years later, I was unprepared for the familiar symbol’s reappearance – this time in Ottawa.

Memory lit up, brimming with the same intoxicating lure. 

It was the other end of the trail:

Yellow-tipped, orange triangles mark the trailhead of the Rideau Trail – the longest trail in Eastern Ontario (387 km).

We are about to find the beginning of some soft tissue trails; we will find the other ends only later in this series.

Tweedles Dum and Dee make an appearance; Fibularis Longus, and Tibialis Anterior.

In episode three we

• learned how the terms antagonist, and synergist apply to muscles, and
• looked at four muscles that hold the hallux square, (all of which insert at the metatarsophalangeal joint).

If you need to jog your memory, then follow this link:

Fauna on the Foot Pain Trail; anchoring the big toe.

This trail marker signals the start of a couple of soft tissue trails that impact your big toe, and arch.

This exactly describes the relationship between Fibularis Longus and Tibialis Anterior.

Dygut and Piwowar (2022) laid out the details in today’s blog:  They describe the impact and interactions of the arch-support muscles, and also their effect on the hallux here:

https://www.mdpi.com/2075-4418/12/12/2945

Figures 1 and 2 show the insertions of these two muscles on either side of the base of the first metatarsal. 

Insertion moves towards origin

Remember: During contraction, muscle insertion moves towards origin – in the case of these two muscles, that is, towards the shin. 

Picture the result: 

• The base of the first metatarsal (the insertion point) rises, while
• the head of that same metatarsal moves towards and along the floor – with the result that
• a strong plantar flexion force perfuses the big toe…

… and the longitudinal arch rises.

Like their codependent, oppositional counterparts the Tweedles, tibialis anterior and fibularis longus are forces to be reckoned with:

Codependent: 

Opposing forces, fibularis longus (Tweedle Dum), and tibialis anterior (Tweedle Dee) need the moderating influence from the other to regulate arch height. 

Oppositional: 

Tibialis anterior supinates the sole of the foot, while fibularis longus pronates it.

Reference these terms from the last episode in the guidebook if needed:

https://ottawamassagetherapy.ca/blog/foot-bridges-ancient-world-wonders-that-factor-in-foot-pain/

Inimitable Force: 

Together, tibialis anterior, and fibularis longus provide, (and evenly divide) 11% of the strength of your ankle and foot

https://pubmed.ncbi.nlm.nih.gov/36552952/

Incidentally, the lift provided by “the Tweedles” relieves the windlass mechanism that we encountered in the last episode.

https://ottawamassagetherapy.ca/blog/foot-bridges-ancient-world-wonders-that-factor-in-foot-pain/

The smaller (intrinsic) muscles (we covered in episode three) are now in an ideal position to do their intended work, and hold square the big toe. 

Thus, functional arches position the big toe to prevent hallux valgus (or bunions).

I told you that two pathologies (arch height, and bunions) intersect.  That would be, here.

Meanwhile, the posterior transverse arch locks in.

With no opposing anchor, the other cuboid bones jostle together towards the anchor.

Concurrently, the upward pull of the Tweedle muscles elevates the main (medial longitudinal) arch, as the body weight shifts from heel to toe along it.

Hiding in plain sight:

Tibialis anterior and fibularis longus lift the weight bearing foot at the arch. 

They rest when you are not weight-bearing. 

Yet, your arch shows to its best advantage while your foot is at rest.

So, what shapes your arch while you relax?

… and the answer is,

Thus, fibularis longus has an antagonistic relationship both with

• tibialis anterior (with whom it attaches on either side of the base of the metatarsal),

and

• tibialis posterior, (with whom it links arms under the foot).

The two tibial muscles work harmoniously for the same end (to invert the sole of the foot).