Muscle Minute Tuesday - The Achilles Tendon

The Achilles tendon is not a muscle, but still worthy of this slot as it is the main connector of two muscles to the calcaneus: the gastrocnemius and soleus. Achilles tendonitis is also commonly listed as one of the top 5 running injuries, occurring primarily just on one leg (even though both legs go for a run).

Origin	confluence of gastrocnemius and soleus
Insertion	middle and inferior calcaneal facets
Action	ankle plantarflexion and inversion OR deceleration of dorsiflexion and eversion
Innervation	tibial n. (S1, S2)
Antagonists	tibialis anterior

The Real World Achilles Tendon

Most consider the Achilles tendon to be one band of tissue connecting into the calcaneus, but a cadaveric study revealed something quite fascinating. The calcaneus is comprised of three facets: superior, middle and inferior.

When dissected, it turns out the medial gastrocnemius connects to the superficial portion of the tendon while the lateral head of the gastrocnemius and soleus connect deep on the medial and lateral aspects respectively. The medial gastrocnemius portion of the Achilles tendon is significantly larger than the other two.

It is common to see medial gastrocnemius trigger points in people who over supinate, meaning this muscle becomes short and tight with calcaneal inversion AND therefore may be long and weak in people who over pronate or have excessive calcaneal eversion.

In a compilation of studies regarding Achilles tendinopathy, reduced activation of several muscles were correlated with this injury: rectus femoris, gluteus medius, peroneus longus and medial gastrocnemius (in order from greatest to least reduction).

Here’s a short list of why this matters:

If an Achilles tendon is irritated, check for weak hip muscles
Achilles tendinopathy is associated with over pronation
The two most common causes of over pronation: weak gluteus medius and lack of ankle dorsiflexion

Conventional thinking says: The Achilles tendon is one tendon that attaches

Real World Thinking says: The Achilles tendon takes an interesting twist with three separate attachments on the calcaneus, with the largest attachment being from the medial gastrocnemius. And primary muscle weakness (or delayed activation) with injury is found in the gluteus medius and rectus femoris.

I have a lot more to say about this. Get your geek hats on, because Thursday, I’ll talk more about the kinesiology of the Achilles tendon. Thanks for tuning in.

Because nobody has time to be in pain.

Until next time…