If you are looking to analyze musculature then I think OpenSim would be your best choice.
Once you get the hold of it you’ll be able not only to analyze postures but also to develop models of musculoskeletal structures and create dynamic simulations of movement patterns.
Agree with the previous answer. If, however, what you are looking for is just a basic joint angle / movement length analysis you should try Kinovea. They allow you to use videos from your experiments, place virtual trackers and extract data out of it. It is open source and available here:
I think to get a relevant answer you need to specify. The question is rather vague. What do you need: 3D-analysis, sagittal view, static-dynamic analysis, muscular component?
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