The point is is that most people lose muscle because they’re not lifting. You will lose muscle if you lose weight no matter the cause, if you are not lifting weights.
I don’t think it would have been possible to not lose substantial muscle mass while rapidly losing 100lbs over 9mo, even with extreme resistance training added to the mix. While DEXA scans are not super accurate, I’ve put on about 17lbs of muscle since my first scan 10mo ago, while maintaining a 12% or less bodyfat ratio.
That said, I’ve been eating extremely healthy both before and after being on the drug which helps a lot. The drug simply gave me the mental space to avoid the binges which were my particular problem. That and it controls portion sizes to European dinner vs. American restaurant sized meals for me.
I was 92kg when I started on liraglutide (I was doing GLP-1 agonists before it was cool!) and 67% of muscle mass (61kg). I'm now at 69kg and 82% of muscle mass (56kg). I'm doing weight and resistance training twice a week, in addition to aerobic training.
One nice thing, while muscles don't become more massive, they for sure become more pronounced and visible with weight loss.
Probably the muscle tissue people lose first are crappy cells. Weak, nonfunctional, senescent or even maybe some muscle embedded fat.
Instead, it's the cells themselves that grow bigger or smaller.