I assume you are a foreign medical school graduate? First, make sure that your education is recognized in the US as being from an accredited institution.
If so, you would have to take and pass Part II of the National Boards. Then, you would be able to apply to numerous Medical School residency programs based on your field of interest. Seek counsel either from your medical school advisor or discuss the matter with an advisor at a Medical School near your home town. The programs that are looking for residency trainees are usually the primary care specialties (FP, GP, internal medicine, and pediatrics). We have too many sub-specialists in the medical field at this time.
a physical therapist must have a doctorate now
To become a physical therapist assistant, you are required to have an associate degree in physical therapist assisting. Licencing requirements vary from state to state.
You cannot become a therapist when you are addicted with Marijuana. A good therapist must not be a patient of any kind of addiction.
A tutorial on how to become a physical therapist can be found from sites offering career advice, including Careers Advice. Becoming a physical therapist requires at least a two-year associate's degree.
you can get fired and not be able to become a physical therapist again or have to restart again with your degree.
No way!
You must be licensed before you can work as a physical therapist (except as an intern). In order to become licensed you must pass a comprehensive examination. That would imply that you are a physical therapist -- or at least trained as one.
There are indeed specialty schools for becoming a physical therapist. There is a lot of school that is involved with this line of work.
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First you need to become a physical therapist. Then you must somehow get contacts to the specific group you are targeting, in this case, "famous athletes". If you manage to get them interested in your services, they might become your customers.
After high school (if you start college right away) it should take about 4 years to become a physical therapist.
A physical therapy assistant is typically at the associate degree level. At present the minimum degree requirement for a physical therapist is a master's degree, and soon to become a doctorate.