Precisions here :



The more you contract, the more the gravity-unloading effect is important.

1) feet are flat on the floor. Legs are relaxed.
2) breath with stomack
3) shoulders are fully supported
4) Don't move the head. The ball support the head "like an ergonomic pillow".
.It is important to maintain the natural "C" curve in the neck for easing gravity.

In human, muscle unloading (by gravity or by prolonged bed rest/immobilisation) decrease strength then induce atrophy.
It seem that anterior scalene is very adaptive, so it make sense.