I looked at spider a few weeks ago after damaging ligaments in both arms.
I'd been out all day at a nature reserve. I always carry my camera + 100-400L resting in the crook of my arm, this is what did the damage
So was looking for an holster type bag.
Must admit I didn't fancy hanging my 7D + 100-400 from my waist.
So I bought the ThinkTank holster with shoulder straps. Works very well, but just a little tight for the 100-400, but I do manage. I've adjusted the shoulder straps so that the holster sits comfortably on my largish tummy and is very easy to quickly bring it into action.
http://www.thinktankphoto.com/produc...ulder-bag.aspx
Harry