i have to say i differ in opinion, i have tried many different training options, i have used one muscle per day once a week, i have done 2 muscles per training session, once a week, and although i did get reasonably good gains doing this, lately i have been using a completely different approach and believe it to be working even better, alot of people might think it is slightly over training, but if protein and calorie intake is kept high, then i don't believe it is.
I am using a 3 day split, training my whole body over 3 days,
2 day's on, 1 day off, one day on, i day off, this way you train each body part twice in 10 day's, instead of twice in 14 days.
i train Chest & back on day 1, Legs on day 2, shoulders and arms on day 3, with this routine i have seen great improvements in my body and strength.
Ju7st my opinion though.