Mocap animation (.fbx) retargeting problem, what kind of method is used for animation retargeting?

Recently, I used Motion Capture sytem (Xsens) to capture complex motion. I can export the motion file as .fbx file so that I can use the animation in Unity3D. But in fact, the real motion’s body dimension (I input subject’s body dimension in Xsens) is different to the avatar’s body dimension in unity3d. But the retargeted motion in new avatar looks quite good even though the body dimension is totally different, I mean , I record the motion from a subject whose height is 175cm, but the avatar I use in Unity3d is shorter or taller. What kind of method is used by Unity3D mecanim system for humanoid animation retargeting? After the retargeting , does the motion feature(joint angle, bone direction,…) changed a lot ? Thank you for your help.

Detail on the system can be found in the Unity blog. I believe the term Unity uses is called muscle interpolation - but I’ve not read the blog content about mecanim since it released. Check the info going all the way back to 2014.