In a human body, support is not something solid. Support is relationship. Support is a balance of elements that aren't solid at all, elements that are incapable of withstanding the weight that presses down on them except as they are balanced. Could you translate this balance as tone? I don't know. I don't know what tone is in words, only in experience. I once equated it with span, but I don't know how to define span. When you get span in a body, you get tone; when you get tone, you get span. Span is a spatial thing; tone is physiological. Both words refer to balanced structure in a living body. Both tone and span indicate a readiness to act and respond that is the touchstone of a healthy body.
--Ida Rolf, talking about Rolfing and Physical Reality, p181