Lats
Work the key muscles to increase the width of your torso
Pull Ups
How to do it : -
Hold the bar with an overhand grip, with your hands wider than shoulder width.
Start the exercise with a dead hang with your arms being fully extended.
Squeeze your lats together to pull yourself up.
Once your chin is at the same level as the bar, pause for a moment and come back to the dead hang position and repeat.