With these pre-requisites it almost doesn’t matter what kind of physical activity one does- the muscles will grow anyway. It’s when you are older and/or accustomed to some kind of physical training, that you really noticeably benefit from resistance training.
And still, that ‘almost’ part does a lot of the heavy lifting here. I don’t believe it’s really possible for a couch potato without any experience to correctly assess their 1RM. People with no experience with pain and effort typically can’t push themselves hard enough, so the entire exercise turns to a half-cardio anyway.
And gauging 1 rep max in a bicep curl is especially difficult (saying nothing of a risk of injury).
I understand the complexity and difficulty of researching the subject, but this entire article is no good and is hardly applicable to most of the population IMO