This is exacting exercise for advanced athletes.
You lock into wide cross-bar (best is with bent ends of cross-bar down to floor). With power of back muscles (not with power of arms!!!) you try to tighten by thorax to the cross-bar.
Thorax is slightly cambered across to the cross-bar.
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
