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Europa Medicophysica 2004 September;40(3):239-46


lingua: Inglese


Bonaiuti D.

Unit of Phyical Medicine and Rehabilitation S. Gerardo General Hospital, Monza (Milan), Italy


In ­this ­issue, we ­would com­plete the con­clu­sions of the system­at­ic revi­sion ­with the ­results ­from the ­major clin­i­cal and experi­men­tal stud­ies. First of all, we out­line ­that the use of ­bone min­er­al den­sity is con­tro­ver­sial and ­opposed of the ­major stud­ies in the ­field ­that ­show ­that the ­bone den­sity is ­only one of the fac­tors ­which ­describe ­bone resis­tance, and not the ­bone qual­ity. In ­fact, ­often, a dra­mat­ic vari­a­tion of ­bone ­strength is ­linked to the ­fact ­that the new­ly ­bone is locat­ed in the ­only in the sur­fac­es ­where mechan­i­cal ­stress is great­est and ­this ­doesn’t ­change com­plete­ly the den­sity. To ­study the opti­mal exer­cis­es pro­gram we ­have to remem­ber ­that the ­ideal tim­ing in the remod­el­ling ­unit of the ­bone was esti­mat­ed at 4-6 ­months: there­fore any treat­ment ­which has the aim of pre­vent­ing ­bone ­loss ­should ­last at ­least 2-3 ­times ­this peri­od to ­ensure ­that the reg­is­tered ­effect on ­bone den­sity is eval­u­at­ed in a peri­od of bal­ance. According to Frost, the ­strength of the ­bone is deter­mined by 4 fac­tors: the mechan­i­cal prop­er­ty char­ac­ter­is­tic of ­bony tis­sue, the ­amount of ­micro dam­age ­from ­fatigue, ­bone ­mass fac­tors (­amount and ­type of ­bone in the ­bone) and the ­size and shap­er of the ­bone (archi­tec­tu­ral fac­tors). Moreover, it is ­very impor­tant the ­role of mus­cu­lar ­strength on the ­bone: the mus­cles ­work ­like a lev­er in ­such a man­ner ­that to ­move eve­ry ­kilo of ­body ­weight, the mus­cu­lar ­force is usu­al­ly ­over 2 kg. This ­explains why ­strong mus­cles are usu­al­ly asso­ciat­ed ­with ­strong ­bones. About the spe­cif­ic ­role of the ­strain on the ­bone, ­from stud­ies of the ­past 10 ­years ­there ­seems to be ­more pre­cise and use­ful infor­ma­tion for our quer­ies: new for­ma­tion of ­bone ­took ­place in rab­bits ­only ­with dynam­ic stim­u­li and not stat­ic, and it is ­very impor­tant ­also the fre­quen­cy of the stim­u­lus and the ­speed. Moreover, ­some ­authors ­have ­shown ­that the stim­u­li of oste­goe­ne­sis ­depends on the ­fluid ­shear stress­es ­though the lac­u­nar-can­a­lic­u­lar net­work ­system. So: exer­cis­es at ­high ­impact ­which can pro­duce sig­nif­i­cant def­or­ma­tion of the ­bone ­matrix, bet­ter car­ry the ­fluid ­through the can­a­lic­u­lar net­work and fur­ther­more the ­strains ­applied at ­high fre­quen­cy stim­u­late in a effec­tive man­ner oste­o­gen­e­sis. Therefore, the mechan­i­cal ­strain nec­es­sary to ­begin oste­o­gen­e­sis decreas­es ­with the ­increase of the fre­quen­cy of the ­strain. Rubin and Lanyon ­have ­shown ­that the pro­lon­ga­tion of the stim­u­la­tion ­with ­strain the oste­o­gen­ic ­response did non ­increase if the reg­i­men is pro­longed ­more. In ­fact, Turner dem­on­strat­ed ­that the ­bone ­presents a phe­nom­e­non of desen­sit­isa­tion fol­low­ing a pro­longed ­strain stim­u­lus. He pro­posed the oste­o­gen­ic ­index of exer­cis­es ­like the oste­o­gen­ic ­response to exer­cise ­which ­could be ­increased in a reg­i­men of exer­cis­es ­which fore­see ­also a peri­od of ­rest ­between ­brief ses­sions of sig­nif­i­cant ­strain. So, con­cern­ing the ­effects of exer­cis­es, the stim­u­lus pro­duced by the ­strain ­must be ­such ­that it ­exceeds a thresh­old of a min­i­mum effec­tive stim­u­lus, ­must be ­applied in a inter­mit­tent and dynam­ic man­ner, ­should pro­duce a stim­u­lus ­which is dis­trib­ut­ed dif­fer­ent­ly to the ­norm, ­should be ­applied ­with ­high ­speed and few rep­e­ti­tions.

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