It's common because our muscles get weak. Think of a marathon runner, and how they have calf cramps. We just get the cramps/tight muscles a lot sooner! So it's basically an "overuse" thing.

And once that pain cascade gets going, it can make things worse if you wait.

It's a "secondary" symptom of a lot of the NM diseases, like MS.



Oh, and heat is okay as long as it's not for a long period of time and if your MG is "okay." I usually don't need to have it on the area for longer than five minutes to make a difference.