Firstly, it is mandatory to always review a job posting before your interview. Secondly, the interviewer will value candidates who reviewed the job posting before applying for this position, and who did not apply to just any position.

As such, by virtue of the duties outline on the job posting, you should already know whether the position will be sedentary, and the answer the interviewer is seeking in a successful incumbent. It is therefore imperative to answer by saying you reviewed the job posting several times before your interview, are aware of the position requirements, and applied as you are perfectly comfortable being in a sedentary job.

Do not simply provide a yes or no answer. Always elaborate.