Merge Running animation with punch

I have a character set up who can run, jump and punch, all the animations have a nice crossfade, however the problem is if he punches and runs at the same time his legs stop moving, the character is originally an animated biped in 3ds max and exported as a fbx, is there any way to tell unity to only read the upper body movements of my character for the punch animation so that he will continue his run cycle?

You want to use a mixing transform. They're kind of confusing to set up until you get one working so you will just have to experiment for a while.

Create a mixing transform, then place the animation in a higher layer and call `Play()`