Do you have to get a degree in physical therapy assistant to become a physical therapy assistant?

Unfortunately, not. The bachelor's in exercise science sounds like a great primer to the physical therapist assistant program. However, the pta needs to have completed an accredited pta program which includes the specialized coursework as well as successfully completing clinical fieldwork in which one would have a patient caseload. They may then be eligible to take the state licensing exam. For general career info: http://www.bls.gov/oco and can search 'physical therapist assistants' or such. http://www.apta.org

Probably not as the Phya Ther Assnt degree requires a lot of work with actual patients, assisting them with their therapy. Some classes may over lap, but not many. It probably is different in each state, as it is the individual states that grant the licenses.