In my opinion once you find the correct training frequency for you, that should never change. What can and should change are excercises and rep ranges. So if you have success training each bodypart once a week, stick with that. You can change the way you split up your bodyparts and what gets trained with what. For me, hitting each muscle group once every five days works the best, sometimes I train three days a week rotating an A workout and B workout over the three days, sometimes when I don't have a lot going on I will do four days on, one day off . My favorite is cycling and A,B, and C workouts over four days a week. The movements change, the sets and reps change, the split changes, but my frequency stays the same.