The human body does not change under suboptimal stress because it doesn't have to. The dogma ex-phys people are still pursuing is that higher reps produce better hypertrophy than sets of five with heavy weights. Hypertrophy is an increase in the size of muscles. The amount of weight lifted, aka intensity, is the primary driver of hypertrophy. 

• 04:19 Comments from the Haters!
• 14:20 Hypertrophy
• 21:41 The phenomenology 
• 31:44 You are not strong enough/Stress management
• 38:35 People are scared of lifting heavy weights
• 50:21 PRs are what matter