جستجوی مقالات مرتبط با کلیدواژه "ستون فقرات" در نشریات گروه "مکانیک"

Footwear condition has been found to change kinematics of body especially in high-demanding activities. The present study compared the kinematics of healthy individuals when different footwear conditions were used. Two types of shoes, i.e., auxetic and conventional, were compared with each other and also with barefoot condition during gait and drop vertical jump (DVJ) activities using in vivo experimentation. A number of 11 male individuals were asked to do the experiments. Three trials for each footwear condition were completed for every participant, i.e., total of nine trials for each person. All methods were performed in conformity with relevant procedures and protocols. Their motion and force-plate data as well as electromyographic (EMG) activities of some trunk muscles were recorded during abovementioned actions. Two main stages of first landing (FL) and second landing (SL) were considered in the DVJ activity. Statistical analysis, using ANOVA and Tukey’s honestly significant difference, was carried out to investigate effects of footwear conditions on the kinematics. Results showed that biomechanical changes between the the three footwear conditions were insignificant in gait and the SL phase of DVJ. However, significant differences were detected during the FL stage of DVJ; using the auxetic shoes resulted in smaller EMG activities in longissimus and iliocostalis muscles, smaller anterior-posterior distance between the center of pressure of ground reaction force and heel, and also larger maximal hip, knee, and ankle flexion angles (p

Soft tissues exhibit viscoelastic behavior, which includes time-dependent creep and stress relaxation, and hysteresis in a loading cycle. Changes in the viscoelastic properties of soft tissues such as spinal ligaments under dynamic loading can cause the damages. In this study viscoelastic behavior of spinal ligaments is investigated by considering two different quasi-linear viscoelastic models under dynamic loading for creep and stress relaxation. After developing equations, the results of formulation were compared with the results of experimental data in the literature and finally, the viscoelastic model that had more accurate behavior to the results of experiments, was choose as the appropriate model of spinal ligament. For this purpose, obtained data by Hingoryani in an experimental study (related to creep and relaxation tests on rabbit medial ligament) were plotted in a log-log graph. According to the graphs, it was found that the strain rate decreased with higher levels of stress and relaxation rate decreased with higher levels of strain. According to the results, present formulation and the obtained constants of the equations had acceptable accordance with the experimental results, and therefore these equations can be used for spinal ligaments with acceptable accuracy.