Résumé :
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Communication n° 633. Neuro-muscular pathologies induce a decrease in musculo-articular flexibility and changes in viscoelastic properties of a musculo-squeletal complex. During a stretch, passive mechanical behavior of such a complex is quantified in vivo by stiffness (S) and stored elastic potential energy (E). Nevertheless, classical methods of data processing do not assess S on the whole range of motion (ROM). This study was then designed to i) calculate stiffness indices (SI) to assess S variations on the whole tested ROM ii) study changes in SI, E and Ed (energy dissipated by musculo-skeletal structures) during passive and quasi-static stretch of hamstring muscles. Eight healthy subjects participated in this study. Passive torque(T)-angle(?) relationships were determined during 5 passive knee extensions-flexions (PEF) performed using Biodex pro 3 ® dynamometer. E (area under extension curve) and Ed (area between extension and flexion curves) were calculated. Two original mathematical models have been used to calculate SI and S i) T=a?^2+b?+c, S1=2a?+b, SI1=2a, 0.973< r^2<0.997; ii) T=(E0/a)(exp(a?)+A), S2=aT+E0, SI2=a, 0.981< r^2<0.999 (a, b, c, E0, a, A : constants). A mechanical adaptation to stretch was shown by decreases of E (PEF1: 586Æ283N.m.°, PEF5: 420Æ197N.m.°, p<0.001) and Ed (PEF1: 294Æ129N.m.°, PEF5: 179Æ68N.m.°, p<0.001), whereas S and SI remained constants (SI1(PEF1)=0.011Æ0.004N.m./°^2; SI1(PEF5)=0.012Æ0.005N.m./°^2; p>0.05; SI2(PEF1)=0.041Æ0.015 1/°; SI2(PEF5)=0.046Æ0.016 1/°; p>0.05). Besides, S assessed from the two different SI were found to be similar to those calculated using a classical method employed in the literature. This reinforces the validity and the interest of our SI calculations respectively normalized by the torque level (SI1) and the ROM (SI2). Considering musculo-tendinous modifications induced by neuro-muscular pathologies, SI, E and Ed could be proposed in the longitudinal follow-up of patients and of functional effects of therapeutic treatments.
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