Squeezing your shoulder blades together or pulling the shoulders back is something taught and retaught for every exercise we seem to do. Overdoing it can be a bad thing, so we should try and find some middle ground.
If you have a very round upper back (think hump) then you do need to think of this as a positive correction. Please continue to squeeze your shoulder blades. But I see so many people who don't have enough space between the shoulders blades anymore, and due to tight rhomboids, their thoracic spine (middle back) gets pushed forward and out of alignment.
Exaggerating the movement for the sake of posture isn't realistic. Watch the video below and I can show you exactly what I mean.
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