Prone Reverse Flys

I have a question regarding this exercise:
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Can we do it standing up, 90° bent with two light dumbbells to activate the muscles more?

I guess it depends on what you mean by “activate the muscles more”, but yes, you can do a standing bent dumbbell reverse fly, and lighter dumbbells are a good idea to isolate the rear delts.

Paul carters Instagram has a good rear delt dumbbells fly/row. It’s what I’ve been doing lately. Not the easiest thing to explain, I suggest looking at his Instagram for a form video.

For my $0.02, try going pronated vs neutral on your grip - I find I get a much stronger rear delt contraction with this subtle tweak