This is the second blog on the AFS Principle of Chain Reaction®. The Chain Reaction® Principle embodies the Truth that motion somewhere in the body initiates a Chain Reaction® throughout the body during functional movements. The first blog dealt with the kinematics (motions), while this one looks at the kinetics (forces) during the movement. Forces can be from the physical environments that act on the body such as gravity, ground reaction force, and momentum, as well as the internal forces of muscle contractions and energy stored during the stretching of soft tissues. These forces, that create torque and power, can be transferred throughout the body. The transfer of internal forces (muscles and fascia) occurs not only to the bones that the muscles attach to but also to body segments adjacent to and even a good distance from the muscle contractions. This validates the Chain Reaction® Principle of human movement.

Research studies have utilized different scientific methods to identify the nature and magnitude of this transfer. These methods continue to improve, but there are still limitations (which may always exist) in our ability to document the miracle of the human movement system. The activity that is studied the most is also the one that is most common – walking. One line of research has been to investigate the role of the calf muscles during gait. A study by Neptune et al sought to clarify the function, and even differentiate between the roles, of the soleus and gastrocnemius muscles during ambulation. Caution must be applied because the analysis was limited to the sagittal plane, and the methods are far from perfect. Their study looked at the contribution of these muscles to support and forward progression of the body during ambulation. They focused on vertical and horizontal acceleration of the trunk, and energy delivered to the leg. 

Here is a brief summary of some of their findings.

  • Although anatomically very similar, the energetic functions were substantially different.
  • Both Soleus and Gastrocnemius contributed to trunk support during single leg stance.
  • In early stance their role is to accelerate the trunk vertically while decelerating it horizontally.
  • In midstance, the Soleus delivers energy to the trunk.
  • In midstance, the Gastrocnemius delivers energy to the leg.
  • In late single leg stance, the Gastrocnemius accelerates the leg forward to swing.
  • In late single leg stance, the Soleus accelerates the trunk forward.

Given the limitations of the study and the complexity of the methods, what are the practical implications for all of us in the movement industry to work to enhance the lives of our patients / clients? Let’s start with the calf muscles providing important resources to the trunk that allow human locomotion to occur. Then, consider the surprising findings about the different roles of the soleus and gastrocnemius given their common anatomical location. Finally, we need to consider the simultaneous roles of acceleration and deceleration in vertical and horizontal directions. All of this speaks to need for movement practitioners to, whenever possible, utilize global body movements to assess and train the kinetic relationships described in this study. We don’t need the exact specifics. We need to provide functional movements that allow the body to discover how to activate and coordinate the body’s physical resources within the context of the physical forces of gravity, ground reaction force, mass, and momentum present in the environment.

 1-Neptune RR, Kautz SA, Zajac FE. Contributions of the individual plantar flexors to support, forward progression, and swing initiation during walking. Journal of Biomechanics, 2001, 34:1387-1398.