When answering this question, you want to keep your answer upbeat. You must never talk badly about your previous job, employer, or coworkers, even if you were unhappy in your last position. And, it is not recommended to answer that you want to make more money or have better benefits. Explain how you want to advance in your career, work at a busier gym, or work closer to home. If you are a new trainer and are leaving your previous job because it was in an unrelated field, be sure to let the interviewer know that is the reason.