According to Greek mythology, Achilles was a dominant warrior who seemed invulnerable to his opponents. That is, until Paris fatally shot Achilles in his heel—the one and only place Paris knew that Achilles was vulnerable.

Those of us that engage in various sports and activities, and those of us who have the privilege of caring for others, realize that our heels, our Achilles complex, is still a vulnerable region of our bodies.

Why is the Achilles complex such a vulnerable part of the body? There are a number of answers to that question. Perhaps the most significant answer leads us to another question or two. So, what does the Achilles complex do (what are its demands) during our sports and activities? Based on that answer, then the next question is as follows: Are we adequately preparing it to do what it needs to do?

What Is the Achilles Complex, and Why Is it so Vulnerable?

The Achilles complex consists of the tendon itself, along with the soleus and gastroc musculatures. It is synergistic with all the other muscles and tendons of the lower extremity, especially with the hip complex. Therefore, the Achilles complex depends significantly on its synergistic friends to deal with the forces and stresses of all forms of function, like walking, running, jumping, accelerating and decelerating, and changing directions.

The Achilles complex deals with the forces of gravity, ground reaction, and momentum. These forces create the motion in the joints that the Achilles complex deals with three-dimensionally.

When the foot strikes the ground, gravity, ground reaction, and momentum integrate with the purpose of the movement, causing the following motions to occur:

  • Subtalar Eversion (Frontal Plane)
  • Subtalar Abduction (Transverse Plane)
  • Ankle Dorsiflexion (Sagittal Plane)
  • Midtarsal Inversion, Abduction, and Dorsiflexion (Tri-Plane)
  • Knee Flexion, Abduction, and Internal Rotation (Tri-Plane)
  • Hip Flexion, Adduction, and Internal Rotation (Tri-Plane)

All of these motions, in all three planes of motion at these joints, turn on proprioceptors that in turn facilitate the Achilles complex along with all of its friends.

This initial facilitation causes an eccentric reaction of all the locomotor muscles, including the Achilles complex, in order to begin to control these motions, which are loading the locomotor system.

As the leg goes through its “loading” phase and transforms into its “unloading” phase, the Achilles complex has the primary responsibility of concentrically inverting the subtalar joint, adducting the subtalar joint, “locking up” the midtarsal joint, while still eccentrically decelerating ankle dorsiflexion.

In Applied Functional Science®, we call this function of the Achilles complex “econcentric.” In all of human movement function, we see muscles functioning econcentrically in order to effectively and efficiently do what they need to do. The Achilles complex functions econcentrically at the foot, ankle, and knee, as well as the hip.

While the Achilles complex is dealing with the foot and ankle, it also is primarily dealing with the knee as it creates knee extension and knee abduction, while still being facilitated eccentrically by the knee going through additional internal rotation. The Achilles complex also deals with the hip by assisting in the extension and abduction of the hip, while the hip continues to go through internal rotation, facilitating the eccentric function of many of the muscles of the locomotor system, including the Achilles complex.

3-Dimensional Movements Are Essential for Authentic Motion

For those of us who were taught that the function of the Achilles complex is simply to plantarflex the ankle, the revelation and truth of the above is eye-opening. It’s also the primary reason we were not able to prepare the Achilles complex for battle.

We need to examine the environments we are creating and the Chain Reaction movements we are facilitating for prevention, performance, and rehabilitation. This process helps us determine whether or not we are facilitating the three-dimensional motions at the foot and ankle, knee, and hip in order to authentically create the motions that turn on the Achilles complex.

We need to then determine the appropriate drivers in order to enhance the Achilles complex to become stable and strong, allowing it to transform its eccentric loading into econcentric power to unload and move.

Creating a Chain Reaction and a Less-Vulnerable Achilles Complex

Our accompanying vlog demonstrates Phase 1 of creating the desired Chain Reaction to allow the facilitation of the motions at the foot and ankle, knee, and hip that the Achilles complex needs to control. This creates the foundation for stability and endurance exercises to facilitate the Achilles complex ability to not only control motion at the joints and movement of the human body but to facilitate the desired reactions.

Applied Functional Science empowers us with the truths and principles of how our bodies authentically function so we can get them to function authentically, efficiently, and effectively; and in the case of the Achilles complex, allow it to become less vulnerable.

Advance Your Understanding With Chain Reaction

If you’re ready to understand the truth of human movement and to use that truth to transform the lives of your patients and clients, you’ve come to the right place. For the last 40 years, Gray Institute has led the movement industry using the principles of Applied Functional Science to give passionate professionals the tools they need to treat and train effectively.

Chain Reaction is one of our cornerstone courses, and has changed the lives of countless physical therapists, personal trainers, and others. To learn more, visit the course page, or reach out to our team to speak with someone about your options directly.

We look forward to hearing from you!