Training a bodypart twice per week has always been shown to be superior to once per week training of a muscle. The problem is with the influx of "Weider Principles" and other bodybuilding trash that's posted in the magazines, the masses have been stuck in the one-bodypart-per-week rut for years.
No strength athletes train a bodypart once per week. Most olympic lifters, powerlifters, and strongman train their backs at least four times per week, and last time I checked, they weren't lacking in back width.
The problem lies in your "full blown failure" which has also been shown to be inferior compared to "near failure." Studies show near failure (i.e. - meaning that maybe you fail at the last rep, or you leave one in the tank, but you don't beat the crap out of your muscles with forced reps, negatives, help from spotters, etc. until you can move the muscel at all) - anyway, near failure is shown to produce as much hypertrophy as total failure with one huge benefit - YOU CAN RECOVER EASIER FROM NEAR FAILRE. Which means that you can train twice as often which provides double the training stimulus which provides double the growth if done properly.
So, my recommendation is: Do the same volume you've been doing, only cut it in half for each workout and train that muscle group twice per week.
The easiest way to do this is to do an upper/lower split.
Matt
