"Lean on” pressure is a relaxing in towards the center of my client's body, allowing gravity to exert itself on my weight, with the least possible muscular effort on my part.
I use my whole body rather than just my arms/ hands / fingers / elbows in isolation, and letting my weight and gravity do much of the work.
This lean-on pressure allows for greater sensitivity, ease, and sustainability.
For the client, this kind of pressure - in contrast to a pressure that comes from muscular effort - is registered by the body/nervous system as comfortable, pleasurable and safe. This supports the body in releasing to gravity, letting go of holding patterns, and deeply relaxing.
Because Shiatsu is most often and traditionally done on a futon/mat on the floor creates further safety for the body. At the neurological level, firmness and ground are recognized as 'safe'. And, again, when the body feels safe, it is better able to release its holding patterns.