@Howlin Mad Missy

It´s not the felxebility. If you start training slow and using the right loading patern your muscle will stretch to where you want them in 2 3 weeks... Under beating i mean that i overtrain them.

@Scrap
For me the most obvious connection is that both of them use the same mechanikal structures. Here i mean that the both treining programs don´t interact directly. The problem comes with the recovery. The kettlebells will increase the recovery time of the barbel training.
I can say about the neurological side of it, that they are both really demanding and this must not be over looked. One can "burn out" much quicker...