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Europa Medicophysica 2004 June;40(2):59-65


lingua: Inglese

The stabilometric evaluation of the erect stance. Energy-based optimal control in a numerical model

Pascolo P. B. 1, 2, Saccavini M. 3

1 Department of Civil Engineering University of Udine, Udine, Italy 2 Department of Bioengineering, CISM, Udine, Italy 3 Department of Biomechanics and Occupational Therapy Department of Rehabilitation Medicine Institute of Physical and Rehabilitative Medicine, Udine, Italy


Aim. This ­paper pro­pos­es an anthro­po­mor­phic mod­el devel­oped in a vir­tu­al con­text, use­ful to sim­u­late the main­te­nance of the ­erect ­stance. Such a mod­el can be ­built ­through a suit­able soft­ware ­which can iden­ti­fy the geom­e­try of the artic­u­lar ­parts and ­place mechan­i­cal con­straints (e.g. ­joints, spher­i­cal ­links, etc.) ­between the sin­gle ele­ments.
Methods. Our ­approach can be ­described as the assem­bly of rig­id ­parts ­linked at the ­joints. The con­trol is giv­en by inter­nal ­torques at the ­joints and driv­en by strat­e­gy for the bal­ance ­aimed to the ­least ­amount of ­total mus­cu­lar ener­gy ­spent. The anthro­po­mor­phic mod­el pro­posed under­lines and ­solves the typ­i­cal prob­lems of a ­system char­ac­ter­ized by a mul­ti­ple num­ber of ­degree of free­dom ­placed in ­erect ­stance and per­turbed by phe­nom­e­na of endog­e­nous and exog­e­nous ­nature. This mod­el is devel­oped via the ­coupling of 2 sep­ar­ate bi-dimen­sion­al mod­els, one rep­re­sent­ing the sag­it­tal ­plane and the oth­er the fron­tal ­plane. The numer­i­cal ­tests ­were val­i­dat­ed ­through experi­men­tal ­tests in a ­group of ­healthy vol­un­teers. For ­this pur­pose we ­employed a sta­bil­o­met­ric plat­form (­force-­plate) to ­record the stat­o­kin­e­si­gram (SKG) on the ­rest sur­face.
Results. The ­shapes of the sta­bil­o­met­ric ­plots ­show a ­good spa­tial sim­i­lar­ity ­between the experi­men­tal and sim­u­lat­ed SKG. Both SKGs ­present a ­good ­range in the fron­tal ­plane ­with con­cen­tra­tion of ­points in ­some are­as (or attrac­tors) in the experi­men­tal SKG, but not in the sim­u­lat­ed one. The ­tests ­also ­showed a pos­tu­ral oscil­la­tion at low fre­quen­cy (≈ 0.02Hz), prob­ably due to the dif­fe­ren­tial tir­ed­ness of ­groups of mus­cles or ­because of a ­delayed ­action of the neu­ro­log­i­cal con­trol.
Conclusion. On the numer­i­cal sim­u­la­tions, we ­claim the suit­abil­ity of the antrop­o­mor­phic mod­el for a gen­er­al descrip­tion of the main­te­nance of the ­erect ­stance. Despite the sim­plifi­ca­tion, ­with our ­approach it is pos­sible to sim­u­late ­some of the ­main char­ac­ter­is­tics of the pos­tu­ral act. In par­tic­u­lar, the ­length and the are­as of the sim­u­lat­ed SKG’s are com­par­able ­with ­those of the experi­men­tal ­tests.

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