Dear all,
I use OpenSim to calculate the ankle moment and the length of a muscle. Subjects walk on a treadmill while marker positions and ground reaction forces and torques are recorded. Data is stored in trc and mot-files and via inverse kinematics, inverse dynamics and the analysis tool in matlab, I try to find the ankle moment and muscle length. Calculating the length seems to go well, but the size of the ankle moment is related to the position of the subject on the treadmill. When the subject walks more in front of the treadmill, the ankle moment seems to be larger compared to walking at the back of the treadmill, so closer to the origin of the force plates.
When I load the scaled footmodel in OpenSim, load motion data (IK-results) and associate motion data to it (mot-file), the ground reaction force appears at the right position on the model. So, I think my input COP and marker positions are right. Does anyone know why the ankle moment is related to the subject's position on the treadmill? The ankle moment I use is calculated in inverse dynamics, because ankle moment files obtained from the analysis tool contain only zeros.
Thanks!