I use two types of magnesium - mag orotate for my muscles and mag oxide for my bowels as they each help in different ways. I'll assume you are interested in the help for the muscles and not the bowels. LOL!
I take 200 mgs of mag orotate daily, and I limit it to that more because of the overall cost of all my supplements/herbs than because of my needs. If I'm having a bad day with lots of leg or arm pain, then I'll take second dose of 200 mgs for a day or 3, then lower the dose back down to avoid raising the cost of my treatment overall.
Depending on what type of magnesium a person uses, it can most definitely cause loose stools/diarrhea, which means the dose has either been raised too quickly or the person is just taking too much for their body to absorb.
I have found this article to be very helpful in what types of magnesium to use:
www.globalhealingcenter.com/natural-health/types-of-magnesium/