The core of your question is one that even professionals can't answer. And frankly, it's not just a question for biomedical engineers and medicine. To counter by example - "Where is the line drawn between Electrical Engineering and Physics?"
The challenge is that the line shifts depending upon the particular application at hand. Likewise, questions asked on StackExchange become licensed under a very permissive Creative Commons license that naturally keeps people from disclosing the true or proprietary nature of the questions they are asking.
Additionally, Engineers routinely work with data or properties that are also used by their counterparts on the Sciences side. For example, both Physicists and Mechanical Engineers deal with levers. But how the Engineer applies that lever can be quite different than what the Physicist would have done.
Biomedical Engineers and Biologists are just one of the more recent pairings between Engineering and the Sciences.
There's also errant assumption behind your question:
I propose that the scope of this site should not include purely medical questions like this one, which do not involve engines, machines or structures because they fall outside the broad definition of what engineering entails. If a biomedical question included the any of these, then that's in-scope.
It's not a purely medical question. What if the purpose of my question is to identify upper bounds of strengths in order to design stabilizing equipment for medical imaging purposes. Sure, you could ignore that aspect of the design and lock them down with chains, but think of how de-humanizing that may be for someone who is already suffering through a crisis in their life?
Biomedical engineers routinely refer to the human body and the various systems within the body as the engines of their systems. For example, can you tell me of a mechanical pump with an adaptive flow rate that can last for over 100 years without external maintenance? There's one in every single human being on this planet.
So yes, I think the question is in scope for the site. And no, I'm not saying that just because it's my own question.
I did think through very carefully before presenting the question. I can certainly dig up references to answer the question on my own, although I'll admit I'm impressed by the one answer it's already received.
I asked the question because the site hasn't picked up any biomedical questions yet and I wanted to stake that territory out before the site goes public. I also asked because I wanted to draw in experts who may be working in that area and could better answer the question than what I could have researched.