Bodybuilding Highlight Muscle Video

I would not be using the position data from Mocha AE. I would be using Corner Pin and probably even a workflow I call Stabilized Power Pin to stop the movement of the tracked area and overlay my graphic. The data you have applied to the Null is not very useful, even if you had a perfect track because the surface (plane) you are tracking changes shape way too much.

If you want to learn how to use Mocha start here with the Mocha Escentials Free version.

It looks like some tape was put on the actor's arm to help with tracking. You are going to have to remove that.

Mocha Pro is expensive. If you are trying to attach a graphic to the arm you might want to consider Lockdown from AE Scripts. It is exactly the right product for tracking the arm and locking a graphic to the movement of the shape. It will do a lot better job of conforming a graphic to the shape of the arm than you can do even with Mocha Pro. 

If you have a limited budget you might want to consider duplicating your original footage layer, applying a boatload of color correction to the footage to improve the ability of Mocha to get a good track, then pre-composing your modified original layer and running your tracking on the pre-comp. I do this all the time with footage that is difficult to track. Try sticking the Logo in Mocha to the tracked arm. If it sticks well, then you should be able to apply corner pin tracking to your replacement layer in the main comp. The Mocha Essentials series will show you exactly how to do that.

The actual tracking is already drifting like crazy and unless you level up to mocha Pro and use its elastic tracker I can't see an easy way how to improve the result. It seems to me you underestimate how bulging the muscles also affects the skin sliding over them, the interstitial tissue warping and so on. That's why your tape markers already will drift. Ultimately that's why on VFX films they paint them on with make-up. In your case you would probably get a lot better results if you forego that whole tracking thing and just animate a Mesh Warp, Bezier Warp, Puppet tools and masks manually. This will be just as quick as spending hours trying to fix your less than ideal track.

Mylenium

Without seeing your footage, your keyframes and so on nobody can tell you much. From frame rate mismatches to spatial inconsistencies due to scene scale this could be anything. You need to be much more specific and provide the relevant info and screenshots.

Mylenium