BMI is also useless for athletes, often giving false reports about their fitness. When I was a serious runner, I once tested my body fat in one of those facilities that uses a pool, so you can get a pretty accurate breakdown of muscle mass to fat.

The test estimated my body fat at about 3 to 4%, which is super low, borderline unhealthy low. I ran six days a week, including usually about 20 mi every Saturday, and you could count my ribs and abdominal ridges. I trained with weights two or three times a week so I could try to keep my body mass up, but that was kind of a losing struggle. If you've seen elite male marathoners, I looked like they do: skeletal upper body with rippling leg muscles. Sadly, my speeds were not even a significant fraction of elite. 🤣

Nevertheless, my BMI would routinely put me at the heavy end of "normal" weight and sometimes even suggested I needed to lose weight.

It really is a useless measure. It's hard to understand why anybody still uses it.