Both Dan and Sam are very specific in their terminology and want it used in a certain way so that they can convey particular ideas clearly.
If you feel tenshijin hurting your back I would stop immediately - ask Dan for some pointers if you see him in November...
Its not as bad now as when I first began tenshinjin, but coming up from jin with your hands pointing up .... whatta stretch!!! I wish I could attend the seminar but alas I am a broke college student!! I will have to ask Heraldo or Frantz to relay the question.