I'm presently deep into animating a character for a graphic novel, and I've run across a common problem, which is animating the classsic 'right straight (or left straight) punch'. It is difficult, because the character is normally lean and muscular, so one can't sacrifice definition, or conversely, give it all away, in a single pose. Here is a solution that allows lots of leeway after the basic pose is created, in terms of smoothness (or muscularity & vascularity) of physique, by not using shape keys, but only careful rigging and weight painting.
My rig is a simple enhancement to the basic 1.1.0 rig, and I've used a more muscular topology to show the solution.
First we start with the rig. I've added a Scapula bone that is parented to the Deltoid. Also the Humerus is parented to the Deltoid (you need this for subtle Inverse Kinematic moves). The Deltoid is parented to the Clavicle, and while the Clavicle is parented to the Sternum, it is not directly connected. This is essential if your character is heavily muscled.
The next step is to create an extra loop cut that more completely separates the shoulder socket from the upper arm. This of course, will depend on the topology one uses, but I've had the same problem from the Alpha 5.1 muscular to the 1.1.0 muscular, so it's just good practice. Make sure your result is all quads!
The next step is to weight-paint the Deltoid vertex group on the shoulder socket. Note the Deltoid is red (weight paint 1, the connection to the upper arm is .5, and the connection back to the chest is only .25, meaning that it won't alter the torso mesh much.
The next step is the pose. Begin by using a constrained rotation on the Z axis of 15 degrees on the Clavicle. This makes the torso movement more natural, than only moving from the shoulder. The Deltoid has a constrained Z rotation of 30 degrees, then the Humerus (upper arm) has a constrained Z rotation of 45 degrees. This is of course all forward kinematics. I'm have inverse kinematics on the lower arm, but I only use that for subtle shoulder and arm movements, to make the animation look more natural.
And here is the result, using a very simple UV texture map, and only level of subsurface subdivision:
This approach is infinitely controllable, as I still have IK and shape keys as my backup.
I hope this helps those who want more realistic fight scenes in their animation.