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I know what you mean about the rounded rear shoulder detail. Unless you're genetically prone to having rounded rear delts that don't develop, there's no reason why you can't blitz them. Obviously, back, trap training will use them, but focusing on just them works better IMO.
Incline Bench Bent-over dumbell raises
Put a bench at 45 degrees ( or slightly lower depending on what feels best) and lay face down on it so the top of the bench is roughly at the top/middle of your chest. Then do dumbell raises. I feel this hits the rear delts more than just bent-over raises. I don't like going too heavy if my lower backs bearing the load, and I feel my upper lats help too much also if I don't use a bench. Being on an incline lets all the stress go to just the rear delt head and again, being on a bench means I can't swing or cheat. You can either sit on the bench or stand, using it as a brace (just watch your back if doing that. Personally, I have one knee up on the bench and the other foot firmly on the floor. This keeps me stable, my torso at an incline angle and allows good form. This exercise did wonders for me. I switched it to my second set in shoulder training, after front pressing to try and prioritise them over my laterals and uprights/shrugs.
Secondly try reverse cable cross-overs. Stand in the middle of a cable station, cross your arms over to the opposite handles, and as if doing an 'upright' lateral raise, pull your arms back across you so you finish in an almost 'star-jump' type shape. Keep your elbows bent a little, and keep the cables at roughly shoulder level to ensure it's you rear delts doing the work and not just your traps/back. For me, this gets a great burn in there and makes them swell up nicely. This can also be done using a chain with tow handles on a single cable, although this wasn't as affective for me.
I do dumbells one week, cables the next and sometimes super-set them. Give it a try.
My rear delt lagged for the longest time. Mostly because I negleceted them and have powerful and overbearing front and side delts... Training first in ure shoulder routine may help. it did wonders for me.
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