Wasting 20% of ur time in the gym then imo. Maybd once a month would be okay.. But once a week...what a waste 
Once a week for that body part, and if you really really want to know, it does only apply to once per month.
Training a body part once per week, and with the current routine I use, that works out to be as follows:
Weeks 1-2 is lower reps...4-6.
Week 3 is 8-10, sometimes 10-12
Week 4 is more of what I explained in the original post.
Then repeat...
So, put whatever percentage on it that you would like. Just don't forget, as I'm constantly reminded daily and post by post, that here at GetBig.com we're all 285lbs and 2% body fat year round.