1. Don’t allow your shoulders to pop outwards as you reach the bottom part of the exercise. If it feels like your shoulders get very close to your ears at the bottom of the pull up, then you are allowing them to come out of their safe position.
2. The undergrip pull up increases the amount of work the biceps do.
3. The overgrip, widearm pull up increases the amount of work through the shoulders and back.
4. The neutral grip pull up is a middle ground between the two.