You may have seen or used this one before but my students love it. I teach primarily women in a variety of classes - bootcamp/kickboxing/sports conditioning and this is one drill I use frequently for upper body.
You will need groups of 3
2 people hold a body bar between them - below the belly button. Hold on tight!
The third person sits on the floor under the body bar - grabs it underhand or overhand (whichever you prefer). They raise their butt off the floor and their abs tight and heels dug in. They then "pull up" - all the way down, all the way up.
Depending on the fitness levels - I usually have them begin with 2 sets of 20 (Holding for a count of 10 at the end). Have them alternate between sets. Believe it or not just holding the body bar with that weight on it is also a good work out. Be sure that the holders don't slouch! If they are too tall they can hold the bar in a squatted position with back straight.
After they have done this regularly for a few weeks - we head over to the "real" pull up bar. They are usually amazed and very pleased at their progress.
This was my first posting and I love this site! You can email me with any questions.