When the Social Security Administration reviews your past relevant work, it considers how you performed that job.  So if you were able to perform that job sitting or standing, but now you can no longer stand for very long periods of time you could be deemed able to return to work.

If you can still perform the easiest job that you once performed, then you are not considered disabled.

Your education level is an important factor used by the Social Security Administration to determine disability as well. According to the Social Security Administration, the higher your level of education the easier it will be for you to perform some type of work.    

  Social Security Disability