Part-time gym jobs can include fitness instruction, facility cleaning, maintenance, sales, and administration roles. Since this is a part-time position, you work less than 40 hours per week. A trainer or fitness instructor helps patrons plan an exercise regimen and guides them in the use of equipment. Some trainers only come to work when a client schedules an appointment, while others work in the facility between clients. The duties of maintenance personnel and cleaners focus on fixing exercise machines and keeping the facilities clean. You may handle your responsibilities after the gym closes for the day. Administrative and sales staff work on client relations, find new patrons, and help existing users manage their membership.