Kelly, Thank you for sharing about your muscle stiffness from your car accident. It is amazing how loose and pliable your muscles can become in the right hands. Heat is especially great at loosening up those muscles and getting them ready to work on.
It is important not to overwork these sore muscles so care must be taken not to do too much in one session or the muscles will be in severe pain the next day instead of relief. Sounds like your therapist knows exactly what to do, probably from years of practice.