If you are familiar with CrossFit you may be aware of ‘kipping‘ pull ups. A kipping pull-up uses the momentum created by the core and lower body to assist with what is normally an upper body movement. This momentum generated by the hips, core and legs assists in propelling the body up to the bar. As a result, this drastically decreases the force production required of the upper body to get up to the bar. Arguably (don’t say this to a Crossfitter!) the more momentum you create with the lower body, the easier the movement becomes. So in effect you should be able to do more reps.
However, don’t be fooled into thinking that because of this assistance, that a kipping pull up is somehow an easy thing to undertake. The kipping pull up is a skill within itself and can be very tricky to perfect. They require more work from additional muscle groups than a regular pull up (shoulders, lats, arms, hips, and core).
For myself when I was starting out with pull ups, a CrossFit friend showed me how to do these. At the time I struggled to undertake more than three or four pull ups. Kipping allowed me to undertake more whilst I built up my upper body strength.