The eternal pull up! These days I have my clients pull up with legs straight and slightly in front, with toes pointed, butt and abs tight, so a slightly different technique to this guy. Apart from that, good breathing really helps strengthen a pull up, chin up or lat pull down. Incidentally, the difference between the pull up and the chin up is the hand position: palms away is pull up, palms face you is chin up.
When we breathe in, the ribs expand outwards. When we breathe out, the ribs contract and one of the muscles that help this is the lats. Part of their attachment is on the bottom four ribs. So when the lats tighten, the ribs contract. So therefore if we breathe out a bit then pull, it helps the lats contract and we pull through the back rather than just hauling away with our arms.
As further food for thought, and maybe a trip to wikipedia, when we breathe in, our serratus anterior should contract, which helps stabilise the shoulders. And makes the blokes look good in their speedos. Plus deliver a knock out punch. Also desirable for us females, but not for the look of the thing.
