As the age old adages say, “Use it, or lose it!” and “Garbage in, garbage out.”
Achieving optimal mechanics and the restoration and repair process for poor mechanics seems impossibly simple: gently demand that the neuromuscular and skeletal systems do their jobs.
The neuromuscular and skeletal systems of the human body continually adapt in response to the way the body is used. It is how they are used and the environments they are used within that determines their overall functional capability.
For example, challenging the body with regular exercise causes it to adapt by strengthening and becoming more capable, whereas the body adapts to a lack of healthy activity by weakening and becoming less capable.
Integral to the body’s functional capabilities is the central nervous system that first collects sensory information through touch, pressure, pain, and spatial positioning before sending signals to trigger muscle activations. The nervous system also adapts to challenges imposed by, or the relative lack of sensory information from, usage and environmental influences.
The Laws of Physiology describe the way that the body adapts
Wolff’s Law of Bone Transformation
Wolff’s Law of Bone Transformation describes how bone adapts to mechanical loading. This Law describes how bones of healthy humans, when subjected to a change in mechanical stress over time, will gradually remodel to become stronger and denser to resist the higher loading, or, in response to lower loading, will become weaker and less dense. The Law also describes how bone shape, structure, and density alter over time as a direct indication of the forces applied to them on a habitual basis. A typical example of bone adaptation occurs in the jaw bone in response to braces that are put on teeth. In this instance, the braces’ rubber bands exert constant tension on the teeth, which is transmitted to the jaw bone, causing the jaw bone to “grow” away from the continuous pressure. Intermittent forces on bone cause the bone to “grow” towards the forces, as observed during bunion formation.
The Mechanostat Model of Bone Transformation
The Mechanostat Model of Bone Transformation describes how bone adapts its mechanical properties (bone mass, geometry, and strength) according to the required mechanical function and peak forces that muscles exert on the bones each day. A typical example of this form of adaptation occurs during heel spur formation.
Appropriate adaptive training with the required threshold forces to the affected bones may stimulate new bone growth, thus preventing or minimizing bone loss.
Trampolining and rebounding are examples of adaptive training. They are so effective at stimulating bone growth, strength, and density that the National Aeronautics and Space Administration (NASA) has used bands and band harnesses with astronauts in orbit to simulate trampolining, thus minimizing bone loss while in a gravity-free environment.
Davis’ Law describes how soft tissue (ligaments, tendons, and fascia) adapt via imposed demands similar to how Wolff’s Law describes the same phenomenon for bone. Davis’s Law also applies to muscle tissue and explains how a muscle will lengthen or shorten in response to stretch or load, respectively. Since most major muscles oppose the function of other major muscles (within an agonist-antagonist pairing), they, along with their synergistic and associated muscle groups, tend to reciprocate each other’s length. For example, a strong yet inflexible Gastroc-soleus (calf) complex will often occur in tandem with a weak and highly flexible tibialis anterior (shin) muscle, and, possibly, vice versa.
Tendons that have lost their original strength due to extended periods of inactivity can regain most of their mechanical properties through gradual reloading, due to the tendon’s response to mechanical loading. Biological signaling events initiate re-growth at the site, while mechanical stimuli further promote rebuilding. This 6-8 week process increases the tendon’s mechanical properties until it recovers its original strength. However, excessive loading during the recovery process may lead to material failure, i.e., partial tears or complete rupture. Aggressive training of the tendon does not strengthen the structure beyond its baseline mechanical properties; therefore, individuals that over train will still be susceptible to tendon overuse and injuries.
Neuroplasticity is the term used to describe how the central nervous system adapts in response to how the body is used. Every body movement requires the intimate, full engagement of the neuromuscular and skeletal systems in an integrated and harmonized fashion. The coordination of limb and body movement is determined by proprioceptive sense (“proprioception”), which provides the brain with spatial positioning of the body and the body’s parts in relation to each other.
The central nervous system is responsible for muscle activations that control the movement of the body. The body’s muscular reflex actions (its innate protective and conditioned reflexes), involve proprioception, which is the body’s ability to sense the relative speed and position of its neighboring parts and the degree of movement. Proprioceptive movements can either be conscious or unconscious (reflexive). With sufficient regular repetition or training, the nervous system adapts and conscious proprioceptive movements gradually become unconscious. In this regard, the colloquial phrase “use it or lose it” is often applied to the maintenance of optimal neuromuscular functional capabilities.
Conditioned Responses: The nervous systems’ abilities are adaptive–their regular use and environment hone their functional capabilities. An initial mindful focus on an activity gives way to unconscious and reflexive movement through repetition.
Similarly, the body’s protective reflex responses become conditioned through use. Protective reflexes are triggered by a variety of sensory stimuli, such as touch, vision, and fearful anticipation (psychological). Brush your hand too close to a flame, and it will reflexively pull away. Trip and fall and, your arms will reflexively extend to protect you before you can consciously respond.
However, when an experienced driver in the passenger seat of a car reacts to perceived danger by reflexively pressing a nonexistent brake pedal, that is a consciously trained protective reflex in action. By repeatedly practicing a new response with sufficient intensity and duration, you can modify a reflexive proprioceptive movement or reaction to an alternative adaptation.
Environmental influences: Environmental influences significantly affect proprioceptive and protective reflex functional capabilities. For example, when an avid writer’s hand and wrist are put in a cast, the functional capability of that area will quickly adapt to the restriction and lack of stimulation by losing much of its “coordination” and strength capability. This lost function, or maladaptation, can be regained by consciously retraining the writing movements through repetition. Over time, the affected area adapts such that that the function becomes reflexive again.
Habituation: The definitions of habituation are:
- the gradual adaptation to a stimulus or to the environment
- the extinction of a conditioned reflex by repetition of the conditioned stimulus
(Dorland’s Medical Dictionary). We can infer that this indicates that the nervous system has a built-in means of adapting to, and ultimately ignoring, unimportant and/or unchanging sensory input.
The body’s adaptability and its effect on gait
When considering human gait, optimal neuromuscular function and skeletal alignment are reliant on a continuous source of varied sensory information. Otherwise, the central nervous system will habituate and ignore a flow of unchanging sensory input. The habituation to unchanging sensory input diminishes or even eliminates the appropriate motor output necessary for optimal neuromuscular gait mechanics.
Understanding this habituation process is critical to understanding how conventional footwear and supportive orthotics and cushioning insoles compromise healthy foot, leg, hip, and back function. It further clarifies that a therapeutic approach is the best means of rehabilitating healthy function.