The worst of the stretching is caused by the way the model is dragged when you click on it.. it forces whatever part you dragged to the mouse's position, the the rest are left to follow at their own pace.
You can adjust how "tight" the bones are with some of the global variables defined at the top, especially with "AngularRigidness" and "BoneRigidness", but if BoneRigidness is set too high, it may cause the body to twitch violently to compensate for small changes.
You can adjust how "tight" the bones are with some of the global variables defined at the top, especially with "AngularRigidness" and "BoneRigidness", but if BoneRigidness is set too high, it may cause the body to twitch violently to compensate for small changes.