Inertia and controlling speed of rotation by changing body shape

Inertia helps us control the speed of rotation.  

If you are performing a front landing and there is not enough rotation, we can tuck our knees in, making the body a smaller shape, reducing the moment of inertia, thus speeding up the rotation.  The body mass is spread further away from the somersault axis of rotation to begin with, so the result of tucking the knees up reduces the moment of inertia and increase the speed of rotation.

Controlling angular speed  using inertia depends upon the  way the body mass is spread about the axis and which axis  of rotation is being used.

If you are using the twist axis, tucking your knees up would increase the inertia and slow the speed of rotation as the body mass is being spread further away from the axis of rotation. making the inertia larger.

It is quite easy to see in this ice skating video that the body starts with a large moment of inertia as the limbs are initially spread far away from the body, gradually the skaters twist rotation begins to speed up as the limbs are brought closer to the body.  The speed then slows down again as the limbs are moved away from the body.