If this is your first interview, probably not. But, if this is the only interview then they might give you a scenario of a client with or without any medical limitations/issues and then either ask you how to deal with that client or they might even ask you to take them though a workout routine. Usually this doesn’t happen in the first interview, but like I said it depends on the gym and the manager. They just want to see if you know what you are talking about and that you posses the skills to work through a specific situation (reasoning). Most of the times before you go for an interview with a gym manager they give you some idea of the nature of the interview process.