dont give up.
i was in your same shoes about three weeks ago. I have been shooting literally for about thirty years now. both compound and traditional. i asked shop owner after shop owner and not a one could ever tell me how to engage back muscles. to be honest i dont think they knew either. they would just say, just pull with your back! so with the compound i did fine without it. just shot low pounds,54#. but when i got back into trad about a year ago, shortly after, my sholders were killing me! i bought some old bear bows off **** in the 30-35-and 40# range and slowly worked my way into each. I got up to 44# +- but i wanted more weigth to hunt with. then i found moebows videos.
Now to your question. watch moebows video!!!
The only thing a little confusing was the j shape he talks about moving your draw elbow in. i kind of see it more of a half circle. the part about closing the door behind you with your elbow helped too. watch his videos over and over again and practice the movement with no bow at first. just move your elbow around and back.
its the first time i have ever known that i was using my back muscles. Iam shooting 48#s now.
Thanks again moebow, and many others whom i gained insight from.
hope this helps.
Steve