Hi there,
Just wanted to add that it need not to be a one way street. 7 Years ago my expansion was diminished to 2 cm or less. I then started to visit my manual therapist (something between an osteopath and a fysiotherapist). With his help, (he manipulates the rib joints to open the beginning fusions) and a lot of exercises, and swimming I got back to 6 cm. Last year I went down the drain again, again back to 2 cm. With more visits, and exercises I got back to 6 again and I feel there might be even more possible.
The most important thing is that you become aware of what is happening. To feel the difference between breathing with the ribcage or with the tummy. When you are a singer, like Kat, or flute player you are aware of that, most of us however will not (you're not supposed to think about breathing normally
).
One thing that helped me to become aware is to place both hands low on both sides of the ribcage and then try to breathe by lifting the sternum or by expanding alternately the left or the right site of the ribcage. It is in the beginning very difficult to be aware of what to do and which muscles to use, but exercise will learn or otherwise the help of a fysiotherapist. When you are aware and sometimes have a good piece of movement (swimming) and someone to check the expansion I believe it is possible to keep it up for most of us. That said it is a lot to be aware of and luckily I live in a country where I don't need to pay separately for my visits.
Gerard
" Support bacteria - they're the only culture some people have."
-Stephen Wright- 
