You lock into cross-bar with narrow parallel adaptor.
With power of back muscles (not with power of arms!!!) you try to tighten by thorax to the cross-bar.
Thorax is largely cambered across to the cross-bar while a motion (whole body centre of gravity is displaced toward forth).
In the beginning is good for good implementation if you try to get head to middle backward bend while a motion.
You breath out with motion up and with motion down you breath in.
Primary:
m. latissimus dorsi
Secondary:
back muscles completely
m. brachii
m. biceps brachii
