Biomechanical analysis has major role in rehabilitation, sports and... researches. Biomechanical analysis software does not exist in our country because current software is too expensive (at least sixty million tomans) to be used in universities and research companies especially Olympic Academy. To this end, the inverse dynamics analysis and biomechanical software is investigated in this thesis. Here, the whole body model is considered as 12 links including head neck, right upper arm, left upper arm, right forearm hand, left forearm hand, trunk, left thigh, right thigh, left leg, right leg, left foot and right foot. The joints are distal and proximal of each link (coincidence to Winter antropometric data). The x and y coordinates of the joints are considered as degrees of freedom. The Newton-Euler method is used to derive equations of motion. Also, the moment at the toe of the stance leg is supposed to be zero in inverse dynamics analysis. In order to validate our code, the following test is performed. A sprint runner runs and two cameras (250 HZ) record his motion. The passive marker is installed on the distal and proximal of each link and on the right and left heel and toe. A force plate exists in the path of his motion. The results of our code is in good agreement with the force plate data with a range of 20% error.Why are some sprint runners running fast? This is an important question for many coaches. Thus, in this project, some of the kinematic and dynamics parameters such as contact time, flight time, length stride and angles of lower extremity as well as forces and moments of the lower extremity are investigated for the elite and beginner sprint runners. Therefore, two groups of sprint runners with the following properties are tested. Elite group includes two soccer players and two 800m sprint runner with the weight of 71.83±5 kg, tall 178±7cm and age of 24±3. Beginner group includes one 400m sprint asian athlet, two young 100m sprint record and one 60m sprint record (inside) by weight of 71.83±5 kg, tall 178±7cm and age of 24±3. Key Words Inverse dynamics, Sprint runner, Flight phase, Single support phase, Swing leg, Stance leg.