Lower backk muscles go before shoulder muscles

I recollect my now-deceased father-in-law being encouraged, in his eighties, by doctors to do exercises that might strengthen his upper back and shoulder muscles in order to counter what were becoming round-shoulders

Now that I am 60, I notice the same round-shoulders tendency creeping up on me

However, on doing the exerices he was recommended, along with other exercises, I deduce that muscles in the lower back start becoming weak first, and that these are what need to be strengthened before there is any chance of the exercises for rounded-shoulders having much effect

Moreover, the muscles in the lower back are the really substantial muscles whereas those in the upper back are, relatively speaking, less substantial

Once the more substantial ones become weak, there is little chance of exercises (that do strengthen the upper back and shoulders) doing much to counter rounded shoulders

On the other hand, once the muscles in the lower back are strengthened, then the exercises for the upper back do help.