Understanding Buoyancy and Body Posture

How do you stop yourself from sinking?

In the red model, the body's weight is stacked vertically.

The water can only push back with a narrow column of support.

Buoyancy isn't enough unless the whole body is submerged.

In the yellow model, the stacking is reduced, and the supporting column

is wider,

but the head is very heavy. Since it's above the surface,

it doesn't contribute to

buoyancy, so the arms and legs must compensate for it.

In the green model, the weight is fully spread out, but

when the arms lift out of

the water, the buoyant force under them disappears,

and the load shifts to the

shoulders. Once the arms return below the surface,

they regain buoyancy.

As posture improves, the column widens, and the body floats back up.

Every limb that rises out of the water becomes heavier, and the body must adjust.

But how exactly does it make that adjustment?