Lit. Heart Mind Body
Shin Gi Tai is Sumoudou concept describing the fact that a Warrior's character is made up of these three parts.
To become a Warrior you must build all these three elements bringing them together around your person as a center.
The three parts mean:
Sumou is all Body only to the uninitiated. Even the little advanced will soon realize the need to acquire the Skill in order to move to a higher level.
But, by far, the most important thing is the Heart, meaning Mind. This is what differentiates the champion from the also-ran. The most important thing in Keiko is the Mind. Everything is geared towards building an indomitable Mind. In Shoubu the Mind will enable you to overcome anyone, no matter his Body and Skill.