Are you physically able to fulfill the various duties this position requires?

Know the ins and outs of the position you are applying for. Let them know you know what it looks like. If there are any gray areas, ask questions. If you have limitations, be transparent.

Not only do they need to determine if you understand the essential functions of the job you are interviewing for, but they also need to know if you have any physical limitations and if it is possible to make any reasonable accommodations for your situation if that is the case. If you don't understand the expectations of the job, then it's clear you haven't done your research and are a less viable candidate. If you are aware of the expectations, have limitations, but are confident in your abilities, then say so and start that discussion.