How to make your form more efficient for rotation (including improving Tuck)

– To get more efficiency for Tuck –

To get more efficiency for rotation when you tuck, you should to spread your legs as wide as you can and pull in your knees to your shoulders by your arms.
And arch your back slightly to make your belly and chest closer to your legs.
Don’t hollow your chest.
You should assemble your body parts to your center of gravity(it is around your waist).

Latter one is more efficient than former one.
To face up lets you arch back more easily and you can make your belly closer to your thighs.
Why is that makes your form more efficient for rotation?
Details are below.

-Rotation efficiency in general-

What form is efficient for rotation?
Probably you know that tuck is more efficient than pike and pike is more than layout in general.
However, few people knows straight from is the worst efficient.
These are because many of your body parts are more close to the axis of rotation in more efficient form than less efficient form.

And the axis of rotation is always the center of gravity(CG) of your body.
(cf. We are always rotating with an axis of waist in the air)
The position of the center of gravity for each forms are below.
(cf. the center of gravity)

In general, CG is around your waist.
Therefore, you should make parts of your body(heads, arms,legs, etc.) closer to the axis(CG) to get more efficiency for rotation.

– Twist efficiency are the same –

We can affirm the same things about the twist efficiency as rotation efficiency.
To make parts of your body closer to the axis increase the efficiency.
It is often (always?) used as an example of increase of twist efficiency that figure skaters fold their arms and draw them in to get more spin speed.