Because the central nervous system (CNS) has such a strong influence on our bipedal locomotor activities and because of the complexity of the human locomotor system, we must take into full consideration that the mechanical function of our feet and lower extremities are under direct and continual influence of our CNS during all weightbearing activities.
In addition, as clinicians that treat musculoskeletal injuries of the foot and lower extremities with foot orthoses, we must also understand that many of the kinematic effects (i.e. effects on joint motion) and kinetic effects (i.e. effects on forces and moments acting on and within the body) that we see with foot orthoses may not only be due to the orthosis directly pushing the segments of the foot into different positions, but may also be due to the neurological and motor response of the CNS to the mechanical effects from the foot orthosis.
Therefore, taking the above into consideration, the two main effects that foot orthoses have on the human locomotor system by their action of altering the magnitudes, temporal patterns and locations of GRF acting on the plantar foot are the direct mechanical effect of foot orthoses and the neuromotor effect of foot orthoses.
The direct mechanical effect of foot orthoses is defined as the kinetic and kinematic effect on the foot and lower extremity that is caused by the change in the location, magnitude and temporal patterns of ground reaction forces that result from direct mechanical contact of the orthosis with the plantar foot.
The neuromotor effect of foot orthoses is defined as the kinetic and kinematic effect on the foot and lower extremity that is caused by changes in sensory input to the CNS from the mechanical effects of the orthosis on the plantar foot that results from alterations in the magnitudes and temporal patterns of motor stimuli from the CNS to the muscles of the foot and lower extremity. The afferent inputs into the CNS that may lead to the changes may come from sensory organs within the skin, joints, muscles, tendons, eyes, inner ears or other areas of the body.
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