Is a way to Morph similar object and record it?

Hi to All, I think this is basically a hard question but I was searching for weeks and havent found a solution so Im making a call to the experts(you) to help me and learn togheter.

What I want to do is from a humanoid rigged A animate to a humanoid rigged B, something like a morph, im not needing a hard morph like a human into a werewolf or something like that, it's a simple human with almost not muscle, and a extreme muscular human, and is something like an "interpolation", a way to have in a clip all frames of the process who turn no muscular to muscular, so I can asign it into a Blend Tree or something like that and in the way the player get stronger a integer make the clip advance across the frames.

As you can see in the next photo, the skeletons are almost the same so in fact it can be probably a simple mesh morph, but i dont find any program that record the process of modify a mesh, letting the skeleton joints unalterable in the process.

I will be all my life in doubt if you can help me :D