Here's how I would do it:  Use Poser Physics to get a figure flopping around on some block set as a collision object.  Capture a couple hundred keyframes from that for the hip, abdomen, chest.  Use ockham's periodizer script to smooth things out a bit and his emphasizer script to tone down the movements (if the Poser Physics collision settings create overly vigorous movement).  Use the graph pallette to adjust the hip rotations until the figure is standing upright (like he/she is lifting a weight.  Use IK to pin the hands (to the barbell) and the feet (to the floor).  Erase the arm and leg parts in the IK chains.  

I would probably also experiment with turning on the hand IK and parenting the hands to the barbell.  That way, the figure could actually be animated lifting the barbell and the hands would follow, even while the torso body parts were quivering.  You could also then animate the position of the barbell so it is moving slightly, like it would if the figure was trying, with difficulty, to hold it in place.