analysis of quadriceps muscles force and activity of a 3-dimensional musculoskeletal model

The purpose of this study was to determine the force of each component of the quadriceps muscles group in different exercises and to determine the activity ratio of vastus medialis to vastus lateralis. for this purpose, a 3-d model of the whole body was formed in the anybody modeling system software. this model that had muscle only in the legs was sitting on the chair and was performed knee extension. muscular modeling in this study was achieved by using a simple model of the muscles. after creating and uploading model in the software, inverse dynamic analysis carried out, and the force and activity of each quadriceps muscle component was obtained. the model was tested in three different conditions: (1) not loading, (2) static training with maximum loading, (3) normal loading. then the force and activity of each quadriceps muscles were examined in gait test. to do this, walking in anybody model was used. in each of these conditions, the force of each quadriceps muscle component and activity ratio of vastus medialis to vastus lateralis was calculated. according to the results, the rectus femoris muscle in not loading mode had the highest value (28%) in creating force. in the static, normal loading and walking conditions, vastus lateralis had the highest value in creating force that were 38%, 42% and 40%, respectively. the activity ratio of the vastus medialis to vastus lateralis in static training, normal loading and gait conditions were 0.92, 0.85 and 0.87 respectively which in static training had the highest value. the results showed that the force and activity charts of the vastus medialis, vastus lateralis and vastus intermedius had exactly similar pattern and they were different from the force and activity charts of rectus femoris muscle. in total, it seems that the results are acceptable in some analysis and are not in accordance with previous results in some others (i.e. not loading condition). therefore, it is necessary to verify and assess the outputs after modeling in this software.