Thanks chaps - you seem to confirm my initial diagnosis that it was the addition of the mattress pad that has caused this muscle pain.

Apart from the odd stupid thing like trying to throw right handed, it's pretty much subsided into a 'don't put your arm there' sort of thing which is getting better all the time.

My arm has no knots or bumps in the muscle but there is a definate 'hot spot' which got treated on Saturday by a method that 98% of doctors would not understand but has worked wonderfully!

The mattress pad has been relagated to another part of the house.

LTS