In these classes you will hold supported postures for longer periods of time (around 3- 5mins) and explore sensations, energy and any movement which arises. This was Developed around Traditional Chinese Medicine meridian lines and used to allow the flow of Chi to move more easily around the body.
You access fascia (connective tissue) when you slowly dive into these poses and intensity may be felt.
So, although the postures may be supported this can be quite a hard practice as the body will be stretched deeply.