I use a hot pad a lot on my neck and shoulder muscles. and my lower back too at times.
look at the height of your chair to your machine. do you have to raise your shoulders to sew? your elbows should bend comfortably, hands not higher. and back straight. i tend to slouch and raise my shoulders. it's habit because i know better. try out different chair heights or raise or lower your machine. some tilt the back of the machine up a bit too.
i also rub in Aspercreme (no odor) and that helps some. good luck.