London's Scoliosis SOS clinic called this exercise the PNF Pacquet, but PNF is short for whatever material a theraband is made of. Or, as my clinic station-mate called it - that pulley thing.
In my case, I need to exercises both of my lats, so I use two therabands. Others only used one or the other. Two therabands are tied to high rungs and I grasp them in my crossed arms, all the while standing in my corrected posture. Then I straighten our my arms and, at the last moment, twist my hands out so that my lats get a good work out (like trying to squeeze a nut). Hold for 6 seconds then repeat 12 times - take a break and do two more sets.
This is one of the few exercises that is reasonably easy to manage while on the road. I put a knot at the ends of each theraband, drape the knots over a door and then shut the door. Ta-da! Easy-peasey.