It all depends on how much grip you have.I am a T-10 para and have been doing pull-ups for a few years.
I had thaught the same thing but where I live it's like pull-up bars are non existent at parks anymore.I got luck that a friend had one that was made from pipe.
What I do is line my self up under the bar and put my legs on a chair.When you first start just do small sets until you build more strength.
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