Originally Posted by Max
I don't have any sturdy chairs and the ones I do have aren't high enough to keep my knees from hitting the ground. And the nearest park or school is 5 miles away and it's 10 degrees outside.
The chairs do not have to be THAT sturdy, I've used folding chairs before with no issues. You use the backs of the chairs, not the seats; so banging your knees is not an issue unless you are around 7 feet tall.
I've rigged up all kinds of chin-up bars in my time. But I'm sure your school has chin-up bars, you do go to school don't you? Otherwise I've built some out of wood or ran a pipe over some chain and attached it to rafters. The only thing limiting you is your imagination and determination.