I am quite sure that you have many experiences that you could write about to impress the committee for admission to the program. What worked for me when writing essays like these was getting a sheet of paper and writing down many experiences that happened in my life.
A Physical Therapy Assistant provides direct patient care in a variety of settings including hospitals, clinics, rehabilitation hospitals, etc. The therapist provides exercise and massages in the treatment of patients.
A few questions to help you with your writing:
Why are you interested in applying to this program? Why are you interested in a program that provides care to patients who are ill? Where did this interest come from? Is there any experience in your life that motivated you to pursue this career of physical therapy? Did you have to care for someone in the past, which motivated you to pursue this career?
Since you don't have any expertise, I would make this essay personal and let the committee get to know you.
I am sure you have experiences and anecdotes, but you have to write it down in paper and open up to the writing process.
I hope this helps. I am here to help you further.