I searched to find if anyone else suffered from the same tension in the left shoulder blade - hits me about 6km when I do a 10km and I too have to pull my arm either behind, in front or let hang - and am relieved to find that it is quite common (not for other sufferers I assume!). I spoke to one of the instructors in the gym this evening and he basically said the same as the physio quoted above - need to strengthen the shoulder blades with exercises similar to rowing (he will show me more when I go next to gym and I will try to explain them on this thread). It is to do with posture and usually affects the shoulder blade that is not regularly used i.e. it is my left that hurts as my right hand is used to write with and use the mouse, etc..... Hope this helps. i am going to check out the links given above too. Thanks for advice