-Well, if you aren't getting paid to do it, we can add Volunteer to the list
-We've got humans + medicine, so we can add clinical.
Not quite sure what your options are, but don't select extracurricular if you can avoid it - I'd classify it as volunteer clinical or clinical research if possible. What kind of app are you filling out at this point in the year?
It is an application to a accelerated program, and I'd much rather put my research in "Volunteer and/or Healthcare Experience" because I initially volunteered for the research, and have contact with the patients when prepping them, but the section seems like they would only like healthcare related activities under that section.
Honestly, you could probably classify it as whatever the hell you want! If you are lacking in a particular area, use this to fill it in. Will it matter? In reality, probably not. If the admissions people really want to look into this activity they will talk with you about it or read a description you'll most likely supply them with.
I'm doing the same manner of research; Cases of a certain disease in my area that I am analysing with an M.D. I'm not being paid, it's real information about patients, so it has clinical applications and possibly real world implications if we get it published.