A kinetic chain (sometimes referred to as a kinematic chain) can be defined as a “combination of several successively arranged joints constituting a complex motor unit” (Steindler).
This functional concept is useful in the study of human movement, because it directly implies that movement (or alignment) at one joint produces, or affects, movement (or alignment) at another joint within that kinetic chain (Reuleaux).
The functional balance between opposing muscles largely determines the alignment and stability of a joint in both a biomechanical sense and within the kinetic chain concept.
Further, there are two basic classifications of kinetic chain:
- Closed kinetic chain – functional movement performed during which the foot (regarding leg motion) is fixed in space and cannot move; thus, the extremity remains in constant contact with the immobile surface.
- Open kinetic chain – functional movement performed during which the foot (regarding leg motion) is free to move that is not in contact with an immobile surface.
Based on these definitions, during gait, the lower limb continuously cycles through episodes of closed kinetic chain (stance phase) and of open kinetic chain (swing phase) activity. The body's challenge is to attain optimal mechanical stability, which by necessity implies that all the ligaments and capsules involved are optimally taut for the foot and entire lower limb as it transitions from the swing phase to the stance phase.
Ideally during normal walking or running, protective reflex muscle activations will occur throughout the "open" lower limb kinetic chain (in the feet, legs, hips, and back) in anticipation of ground contact. These muscle activations should optimally align the "open" lower limb kinetic chain and prepare the limb to be capable of safely and efficiently managing the forces encountered throughout the "closed" lower limb kinetic chain, while the feet are in contact with the ground.
The vast foot-related lower limb kinetic chain problems occur because “open” lower limb kinetic chain reflex muscle activations fail or are inhibited due to footwear use.
To fully grasp the many manifestations of foot-related lower limb kinetic chain problems, it is helpful to understand the lower limbs' "ideal functional state" when walking and running. That "ideal state" can only exist when the feet function in an environment that facilitates varied stimuli to the soles of the feet (Right Stimulus) and unrestricted foot movement (Right Movement), as observed in barefoot populations with few debilitating foot-related pathologies.
The innate protective reflex and optimized neuromusculoskeletal function and alignment of the habitually barefoot are a direct result of the minimal tissue stress and degeneration that occurs throughout the lower limb kinetic chain during day-to-day activities. This dynamic weight bearing "sweet spot" function/alignment provides us with a model of optimal gait technique.
It is useful to think of a shoe-wearing foot as a fettered structure when considering why specific lower limb gait-related pathologies occur. When viewed this way, it is easy to conclude that the shoe-wearing foot is totally or partially immobilized.
Common forms of immobilization:
- Regular footwear
The effects of immobility in the creation of pathology:
- Immobility can be the cause of many pathologies
- Immobility can lead to functional maladaptations
- Functional maladaptations can lead to acute and chronic pain
In the words of R. Gotlin, author of Sports Injuries Guidebook, “Simply put, function is the outcome of any activity.”
Physiologically speaking, our body function is governed by Wolff’s Law of Bone Transformation, Davis’s Law (of soft tissue adaptation), and neuroplasticity (the adaptive capabilities of the nervous system).
Generally speaking, the quality of the function and alignment of an individual’s kinetic chain is a predictor of future weight bearing degeneration and resultant gait-related pathologies.