Modeling Muscles Work that Provide the Horizontal Balance of the Pelvis at Single-Leg Standing
In this paper using mathematical modeling we had calculated forces and moments of force of lumborum, pelvis and lower extremity, providing of horizontal balance of the pelvis. In contrast to works performed earlier except muscles of «pure» (obligate) abductors, in the calculation scheme we considered the action of all other muscles, vector of which is more lateral then the centre of pelvis rotation at singly-leg standing. To the optional abductor we referred piriform, iliopsoas, tailor’s muscles, straight portion of the quadriceps and anterior portion of the gluteus maximus.
The calculations were based on the concept of keeping the horizontal balance of the pelvis due to operation of the actuator in the form of muscular system by traction forces developed by individual muscles. Actuator action is regulated by the central nervous system, which generates control signals representing a control function of regulation changing with time. Various receptors perform both external (information about the environment and position of the body in it) and internal control (state of the system and its elements). Based on the data of control system, there are being produced coefficients of regulation affecting the magnitude of regulatory functions.
In other words, in changing one variable of control function, maintaining balance occurs due to changes in other variables.
The calculations revealed that obligate abductors (small and middle gluteal muscle and musculus tensor fasciae latae) provide a force moment of 80 N•m, which a little more than 2 times exceed force moment of gravity (34.6 N•m) at quiet single-leg standing. Total proportional traction of optional abductors allows providing force moment of 66.8 N•m, which is not much less the moment created by obligate abductors. The total moment of the force of all the abductor is 146.8 N•m, which is more than four times higher than the force moment of gravity. And it is that the safety margin that allows horizontal pelvic balance even under extreme dynamic loads.
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