Most gyms and exercise programs will request or require that you get a check-up to ensure you don't have a health problem that could be made worse by certain types of exercise. But medical conditions such as diabetes and heart disease can sneak up even for active people, so don't skip your yearly check-up. Discuss your fitness plans with your doctor, especially if you have a preexisting condition or are on medications. Most often your doctor will applaud your decision to get more active, but may have some restrictions or cautions if you have certain health problems or risks.