I’m not walking it back. Initially I simplified it so that the average person could understand it, then you came in guns blazing and turned it into a scientific debate, making it seem like muscle density doesn’t exist at all as a concept. I didn’t want to make it complicated for people just starting out, all beginners care about is results, they don’t really need to know the science. You usually end up learning as you go anyway.

The fact is that muscle density, muscle size, and functional strength are all variables. Both muscle density and muscle size increase strength, which I think was our misunderstanding.

• You can have large size with low density, which is still way stronger than doing no exercise at all, of course. That’s what I was referring to before with my puffed up comment. Not useless muscles, just less muscle per muscle. Still muscle, still healthy and helpful.
• You can also have low size with high density. This is the “skinny strong” I was referring to.
• But best of all you can have high size with high density. The effects multiply on each other. I imagine this is the one you’re helping people create.

Of course, if you exercise, you will gain size, but depending on how you do it, you may gain more density than size per unit of time in the gym. You’ll always get a bit of both though. It’s a ratio thing.

To answer your anecdotal question, I do know someone who just cannot put on bulk for some reason. I suspect it’s either an undiagnosed medical disease, or very unlucky genetics. Anyway, they work out a lot, and are much stronger than me or many people I know, despite being “wiry” and smaller. Their arms are like corded steel. They continuously get better results every month, though I think they might be hitting some sort of upper limit in how much muscle that can be physically crammed per square centimetre of body tissue.