I can't work the 2 muscle groups of bis and tris only and make that the workout. Can't do it. So, I typically do not do either 1) train 1 body part per day, nor 2) splits training
I only ever do the following:
--my own freestyle total body weight training (based on a mish-mash of Cathe DVDs), going as heavy as possible, all muscle groups covered, 3 sets of each exercise, at least 2 exercises for each of bis and tris, 3 for shoulders,chest and back: at least 7 different exercises for lower body, 3 sets of each
--an upper body split using a Cathe DVD: PUB, CTX upper, 4DS upper, LIS Trisets for upper or a KCM DVD
--I like to do Xtrain chest/back/shoulders on its own.
--I do a mash-up of multiple compound moves from KCM DVDS that hits ALL MUSCLE GROUPS CONSTANTLY, hence no need for splits.
This approach works just fine for me: I have clear muscle definition in bis and tris without ever doing a bis and tris only split.
Clare