EDT I love Charles so don't take anything I say as a criticism about his person. He is incorrect. "Work" does have something to do with hypertrophy, but only as far as peak tension (not intensity or effort) achieved and the duration of that tension (not to be confused with sets with less weight due to fatigue). You are pushing the limits of your strength-endurance by trying to increase the number of reps with a fixed load within a given amount of time. The %1RM relative to your level of conditioning at the time will dertermine how effective those sets will be for growth. Once the muscle adapts to using (lifting & lowering) your 12 RM, you will stop growing. However, if you continue to stress its metabolic/oxidative capacity, it should increase its ability to resist fatigue with the 12RM load. In other words, once you have stopped growing, you might continue to get better at lifting your 12Rm while exhausted as long as you make lifting your 12RM more exhausting over time by reducing the rest periods. So the method will work as long as you can continue to increase the weight.