Primary: what the exercise is chosen to train. Secondary: the muscles that help or hold you steady.
How to do it
Set a bar or rings at about waist height — a table only if it cannot tip: pull from the middle of a long side and test it first. Hang underneath with straight arms, heels on the floor.
Brace so the body is straight from heels to head.
Pull the chest to the bar, squeezing the shoulder blades.
Lower under control.
Common mistakes
The hips sagging — squeeze the glutes and brace.
Pulling the chin up instead of the chest — lead with the chest.
Too hard to finish reps — bend the knees or raise the bar.
Skip this with a back, shoulder, elbow or wrist injury unless a professional has cleared it. General fitness guidance, not medical advice — stop if anything hurts.