When you think about it this is a very complex problem. Obviously you have to consider your stance as ravenge has said about his bad back. With Paul H and his height a low lathe would really cause problems. I quite like tucking a chisel under my arm for hollowing but could do with the lathe higher for general work.Depending on your lathe height and your height your chisel grinds may vary too.Also, in the winter I tend to keep more shavings on the floor than I should(I know,I know, I'm the H&S guy and should know better but this is a fact of life that I keep more shavings on the floor to keep my feet warm)and the extra layer of shavings will affect your lathe height too. There can't be many turners who stand upright to turn, I am a leaner, I always have to lean against the machine as that is how I am comfortable.
I'm glad I'm not the only one to rattle my funny bone on the tailstock and it certainly isn't funny!
Paul D the best advice I can give you is work comfortably, try not to stoop and turn with your knees slightly flexed, do not stay in one position on the lathe all day long as that is not good for you,if I have a long monotonous job I move my sharpening system so that I walk about in the workshop to ease the joints a bit.
Hope this helps
Regards
John BHT