i train every bodypart twice a week except delts it works out fine , each part gets 3-4 days rest before workin it again , train chest n tri , back n biceps , quads hams clvs , delts n traps .
3 exercises per part for 4 sets of 8-10 reps pyramided to failure.

i used to train each part once a week , got slow growth , this way my arms are over 18" almost 19" all gear free ...........remember the champs back in the days all trained each part twice a week , all had good arms , gear use was limited , no gh , no insulin.

its your call.