I like to play standing up, cos it's better for singing and general presence. And I've always used a kinda long strap, cos I strum a bit, and I get cramp in my right shoulder if I use a shorter strap. However, for some tricky finger style stuff, the left hand just can't do what it has to do. Recently I've shortened my strap and presto! - my left hand's great. Quantum leap. However, the old right shoulder's starting to accumulate a cramp.

Any thoughts/observations/tips greatly received.

(Personally, I blame the basic design flaw of the straight guitar neck. Now if it were to bend a little the left and right hands could both be at an ideal height)