Is there a way to quantify the "expected" muscle loss associated with extreme weight loss? I mean, for people who go from 400 lbs to 150 lbs, prior to the weig

Is there a way to quantify the "expected" muscle loss associated with extreme weight loss? I mean, for people who go from 400 lbs to 150 lbs, prior to the weight loss, they were essentially doing a 250 pound squat ever time they'd get up and out of a chair. I assume most people don't start taking up weight lifting, so then they'd lose a lot of muscle mass they are no longer are using.