3 questions correspondantes
You need to dress professionally in a way that reflects the job description. Your attire is directly considered in the post interview evaluation.
Wear casual or sporty clothes that show off your physique. They want to know that you are interested in physical activity, especially if you are applying as an instructor.
The YMCA does not have any dress codes that I know of. The YMCA is open for everyone in the community, making sure that everyone feels welcome and accepted.