Pull ups are a great way to test and build overall strength. There are many different ways that one can grip the pull up bar and the different grips will work on different muscle groups. Doing different variations of pull ups will be beneficial in buildint overall strengths. My favorite pull ups are with the palms of the hands facing away from the person. These pull ups are usually more diffictult to do and largely focus on the back muscles along with some muscles in the upper arm. The most important thing when doing any pull ups is to make sure that you come all the way down so that the arms are extended and then go up until the chin is over the bar. When someone is trying to do as many pull ups as possible it is recommended that once the chin gets over the bar that they just let their boday drop. This helps in a couple of ways. First, your body is using muscle strength when it is lowering the body down as well as on the way up. If the person just lets their body drop most of the strenght that would have been used to lower the body slowly is now conserved. The second reason it helps is that the person can use the natural elasticity of their muscles to give them a little advantage on the way up right after they come to a dead hang. The other most common variation is with the palms facing towards the person doing the pull ups. This works mostly on the bicep muscles and is usually easier. The same fundamental concepts are used when doing these pull ups. There are also variations in which someone can have a grip with hands very close ore very far apart, utilizing different muscle.