BMI is designed to get an idea about the degree of obesity someone is suffering with, people with muscle mass should be using tape measure or caliper to get an idea of health. My understanding is that the body fat % is what would matter more so if someone has a lot of muscle mass, they'd put that % into a calculator to get a more precise calculation. I don't know much about it but that is the idea I am getting in general.
For me personally, My body fat % is high because I never gained muscle when I was a teen, and have been either overweight or obese for the last 18-20 years. So there is no point in using a caliper or tape measure to get a %. I've always been under the impression that BMI scores are only for people that are overweight and obese.
Note too that I may be incorrect it's just the information I've been picking up from around the internet.
Now That's what Steve would say to you, now if Steve was playing the character of Ghert qux, He would say
"you need to get a prescription for Askfatalin, Askfatalin is a medication that you take that contains microscopic aliens, that get into the digestive system. These microscopic aliens enter the blood stream, and have a conversation with fat cells to get an overall understanding of what is going on. The aliens then go back into the digestive tract, and you will vomit them back up. Then you put them into a machine, in which converts the aliens to a size of a human. Then the alien will let you know what your body fat percentage would be. Sometimes you may get lucky and the alien will let you know if you have HIV or hypochondria