Posture affect your shoulders but it is not the only thing to cause RSI problems. I have RSI in my shoulders which affect the trapezius muscles. This can be very painful and having had physio and been taught how to sit, exercise etc have not seen a great deal of improvement. I do have to do a repetitive job that involves sitting with my arms held at shoulder height and head bent forward for a good deal of the time. Also seating is a big factor with this problem and not all firms will give you the correct seat. This type of injury does seem to affect just a few people and therefore there seems to be very little information available.
Comment 1: Just like to add that bad posture may not just mean slumping forwards. In my case I hold my shoulders back (the classic chest out, chin up thing) and I have to retrain my body not to do that. I do lots of other bad things, like lift my shoulders, so I’m effectively holding my arms up slightly and I also pull inwards, via the armpits, if you can imagine, so there is tension running down the side of my ribcage. I have almost constant tenderness in my left armpit and across the collarbone. In fact if I prod most of my ribcage, it’s tender. I have been diagnosed with Diffuse RSI and absolutely nothing else has been found to be wrong with me.
Comment 2: Your work position sounds terrible for your shoulders! It seems to me that once injured, the muscles / tendons etc are so vulnerable that they complain VERY quickly if you again get into the position which caused the problem. I first thought I must be imagining things when I only needed to SIT in front of a computer for 5 minutes before my shoulders and hands started hurting! I think posture, frequent breaks and appropriate exercise are vital. However, it all still takes a very long time to improve matters it seems, unless you are lucky or have taken action early enough. (I can only speak for my own experience of diffuse RSI).
Comment 3: Interesting discussion on shoulders. Everyone seems to assume that posture is at fault. After many doctors looking at me they said that my posture was fairly good for someone born with a slightly curved back. Makes you wonder whether if it was picked up earlier I may have been able to do something about it. Oh well!!
Comment 4: My experience with an Alexander teacher is that what ‘the world’ (including doctors) calls ‘good posture’ is nothing of the sort… you may be able to improve things even now. It’s helped me enormously – I had the sort of ‘good posture’ that dancers are trained into – actually very strained.