Myth Busting with the Soleus
Why does it take so long to change people's minds about certain things?
We can’t all know everything but when it comes to movement health part of my job is to educate.
This post is equally about a calf muscle called the Soleus and about paradigms that need changing, like pronto.
Each myth I address is probably worthy of an individualized post. So I acknowledge the debunking explanations are not complete and yes, context is always Queen :)
The Soleus muscle is going to be my guide as I address some false beliefs that persist out there in the world of rehab and fitness. This info might be old news for some but if not, I hope you learn something.
First off, let me introduce you to the Soleus.
The Soleus is a multi-pennate muscle in your lower leg. One of the two calf muscles whose tendons form the Achilles tendon, the Soleus lies deep to the Gastrocnemius.
Proximally the Soleus originates from the soleal line, posterior surface of the tibia and head of the fibula. It attaches distally to the calcaneus via the Achilles tendon.
Now let’s bust some myths!
Myth #1: Muscles only move the joints that they cross.
Anatomy is still introduced in a simplified way: you bring the muscle’s “origin” to meet their “insertion” and Voila, you have their “action.”
It’s more involved than that. The individual and the context matter. Muscles produce force in different ways, depending on multiple factors including: their architecture, osteokinematics, position and load (especially gravity). Muscles work together with other muscles. And YES, muscles can produce movement at joints that they don’t even cross.
The Soleus is what we refer to as a one-joint muscle in that it crosses only one joint (your ankle). You’d think that simplifies its actions but then you’d be thinking too simply. The Soleus is a flexor, an extender, and a stabilizer.
Most anatomy texts you read will tell you the action of the Soleus is plantar-flexion (flexing your foot so your toes point down). While true, this is not the whole story. The Soleus also works eccentrically to control, or decelerate, dorsiflexion at the ankle.
In closed-chain when the distal attachment of the Soleus, the calcaneus, is fixed (ie the heel is on the ground) the Soleus is able to influence not only the ankle but the knee as well.
At the knee: A contraction of the Soleus when the calcaneus is realtively fixed on the ground produces a posterior (backward) force on the lower leg helping to extend the knee.
Read on to find out why this is important.
Myth #2: You should never allow your knees past your toes
I hear this from patients all the time. They have been convinced that their knees should never move past your toes. Is this right? No. Are there exceptions? Yes.
There are times when this might be good advice but it’s not a hard and fast rule.
The biggest problem with this myth is it is taken too far. Out of fear I've had several patients who don’t let their knee get even close to their toes! Limiting the natural excursion of your lower leg forward to go down stairs or sit down in a chair can potentially cause increased stress elsewhere.
After knee surgery patients are typically trying to gain range of movement back at the same time as they regain function (walking, going up and down stairs, sitting down, landing etc).
There are many examples of exercises where this is applicable (various forms of squats, lunges, step downs) but let’s talk about function.
The Soleus is involved in a step down movement, aka landing. In fact research showed that landing from higher step heights the Soleus played more of a role in increasing posterior force on the In this role, it serves as an agonist to your ACL.
Which leads me to my next myth...
Myth #3 ACL rehab (and prevention programs) should focus only Quads and Hamstrings
Oh and don’t forget those Gluts (just being cheeky…LOL) The truth is any "prevention" and rehab program should focus on the patient in front of you and what their specific needs are. A lot of attention is given to the Quadriceps and Hamstrings and rightfully so. Wrongfully so though if you ignore calf weakness, especially in this population.
As noted above, the Soleus has been shown to act as an agonist to the ACL in single leg landing movement.
As ACL rehab progresses agility drills are usually added. An interesting modeling study showed that the Soleus (in addition to the Hamstrings) were the muscles that generated the greatest posterior shearing force to the tibiofemoral joint during unanticipated sidestep cutting maneuvers. These studies demonstrate the Soleus has the ability to counteract ACL loading in the sagittal and frontal planes.
So isn’t it starting to sound like this little-ish calf muscle might be important to train?
My next myth addresses this in a population I've found to have some misconceptions on strength training…runners.
Myth #4: Runners shouldn’t strength train
Multiple studies show that not only will strength training NOT negatively impact your performance it can actually boost it.
Both the Soleus and the Gastrocnemius are critical in the forward propulsion of running, but its actually the Soleus that displays the biggest effect on upward mass center acceleration (at all running speeds). It can produce a ground reaction force of 2x bodyweight!
One of the reasons some endurance athletes shy away from strength training is the fear that the added mass will adversely affect their performance. They don't want to get bigger.
Ah yes, the age old debate on whether size matters.
Myth #5: Bigger is better
Does size matter? It depends.
Matter for what? & How do we define size?
Size, is one factor that influences strength. Muscle architecture matters. What's that?
A muscle’s architecture determines how it will function, the capacity it will have to produce force and the speed at which it will be able to contract. One of the key factors of muscle architecture is physiological cross-sectional area (PCSA). PCSA is an indicator of a muscle’s maximal force potential. This is different than cross sectional area.
Most people don’t think of the Soleus as being a big muscle but it has the largest physiological cross sectional area (PCSA) out of the lower extremity muscles. That means it is capable of producing a relatively large amount of force.
Now imagine its weak. Hmmmm. You best be loading that “small” muscle.
Myth #6: Tendinopathy treatment is all about eccentrics
The research focused on tendinopathy is some of the most exciting and dynamic in rehab right now. By dynamic I mean it changes. As a clinician, it can feel akin to keeping up with Game of Thrones. If you don’t stay current you won’t know who/what has been killed off and who/what is still in the game.
Progressive loading is the cornerstone of tendinopathy treatment. Do you start with isometrics? Focus only on eccentrics? Or load heavy and slow? It depends. Most current studies support the use of both concentric and eccentric modes when strengthening past a potential isometric phase.
Intervention should be individualized, combining a knowledge of the science with the specifics of the patient in front of you.
How you load a 60 year old fitness walker who developed heel pain after a dose of fluoroquinolone antibiotics is different than how you treat a 30 year old elite runner who developed Achilles pain after a ramp up in mileage.
When loading for Achilles tendinopathy you shouldn’t forget about the Soleus.
Achilles tendinopathy (AT) research shows that Soleus is the most involved muscle in that individuals with AT have more significant loss of Soleus muscle force generating capacity than Gastrocnemius.
So if you are only doing exercises targeting your calf muscles with a straight knee you should add bent knee ones as well. In his PhD dissertation Seth O’Neill cites several sources that support the use of knee flexion to better emphasize Soleus force production.
To end this post I want to give the Soleus just one more bit of love. After all, it is referred to as the second heart.
The Soleus is called the second heart because its strong contractions help with venous return, pumping your peripheral blood back to your heart. Lastly, if you happen to work with clients/patients with congestive heart failure (CHF) the Soleus muscle is proposed to be a sentinel skeletal muscle muscle in people with CHF.
Pretty cool little muscle.
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