Résumé :
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Communication n° 626. Muscle stretching exercises are used for functional rehabilitation and to limit the decrease in joint flexibility induced by neuro-muscular pathologies. Nevertheless, effects of stretching are discussed and seem to depend on experimental protocols. The aim of this study was to assess acute effects of standardized static stretching on hamstrings viscoelastic properties using two mathematical models. Eight healthy subjects participated in this study. A Biodex pro 3 ® dynamometer was used to measure resistive torque (T) offered by hamstrings, and knee joint angle (teta). Stretching protocol was composed of 4 30s-static stretching at 80% of the maximal range of motion (ROM). Before and after this protocol, 5 passive repetitions (PR) of quasi-static stretching up to 80% of the ROM were performed. For each PR, potential elastic energy (E) and dissipated energy (Ed) parameters were calculated using passive T-teta relationship. Two stiffness index (SI) were calculated describing stiffness (S) change with ? (SI1) and T (SI2) respectively. After static stretching, an increase in the ROM (+11.5Æ6.8%, p=0.002) and a decrease in E (e.g. for PR1: -25.8Æ23.1%, p<0.001) and Ed (e.g. for PR1: -16.5Æ14.2%, p<0.001) were calculated. S characterized by means of our two mathematical models was similar to S determined by a classical method. Then, S globally decreased (p<0.05) after static stretching. Besides, IS1 decreased after stretching (e.g. for PR1: -21.1Æ21.5% p=0.002) whereas IS2 remained constant (e.g. for PR1: +6.6Æ31.4% p>0.05). This could be explained by a decrease of the maximal T after stretching (e.g. for PR1: -21.0Æ16.9% p=0.002). The decrease of S after stretching is not always found in the literature. Nevertheless, combined with the decreases of E and Ed, this evolution could partially explain the increase of the ROM after stretching. Lastly, these changes could be discussed in terms of passive structure contributions to force production modifications after stretching.
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