This movement works best if you use bands. It's a short range of motion movement so the constant to tension helps fatigue the muscle more efficiently. Set them up pulling forward (first video) or straight down like the second video. Pulling forward is the most difficult option. The yoke bar also makes this movement more difficult.
Sit on a bench or box with your feet wide like you are squatting. Drop your chin and roll your upper back over. On the way down flare your elbows out to the side (second video shows this better) and push your scraps out on the way down. To reverse the weight pull your scraps and elbows back, down and in and arch your head into the bar. Hold in the top for a second. KEEP TENSION ON THE MUSCLE! Don't roll over so far that you don't have control of the weight. Keep the weight relatively light. Before this set I squatted 6 plates on that bar and a 25 on each side with the band for 4x20-30 was enough to torch my back.
To make this more difficult reverse your breathing. Exhale on the way down and inhale on the way up. This takes away the Valsalva effect. Then when you fatigue that way switch to normal breathing and get some more reps. It's also good to add a static hold at the end of each set when you feel you can't complete anymore full reps.
We typically used this with our more advanced athletes. This would also be very effective with over head athletes and done with wrestlers for time.
SSYOKE BAR