"I’m not saying that light pump training doesn’t work for natural lifters. Hypertrophy can be stimulated with light weights if you go to failure. The problem is what happens in the body when very high reps are combined with light weights. Sure, you’ll eventually get maximum muscle-fiber recruitment as you build fatigue during the set, however, if it takes you 15 or 20 reps to “get there” instead of 6 to 8, then you’re spending twice as much glycogen to achieve the same effect.
Remember, the more energy (glycogen) you need to mobilize, the more cortisol release you’ll get! That’s why super-high rep work is not ideal for natural lifters, especially if you do a lot of sets."