If you cannot do any pull-ups, you should try "negatives". Negatives are half pull-ups. All you have to do is get your chin over the bar by standing on something or having spotter push you over the bar. Then, you slowly lower yourself all the way down - let your arms hang grasping the bar fully stretched. Keep your feet up and fight gravity for a count of 5 seconds. This will get your arms used to supporting your weight.
Assisted Pull-ups - This is the first step to being able to perform pullups. Using the bar that is 3-4 feet off the ground, sit under it and grab with the regular grip. Straighten your back, hips, and slightly bend your knees while your feet remain on the floor and pull yourself to the bar so that your chest touches the bar. Repeat as required. This is a great way to start out if you cannot do any pull-ups at all. You can also do this on a pair of parallel bars that are used for dips. These are also great to do after you can no longer perform anymore dead-hang pullups. This is a good replacement for the Lat Pulldown machine as well.
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