Who cares if you're never sore? Soreness doesn't matter and is not an indicator of an effective workout. Why don't you try doing 200 reps of triceps pressdowns - your muscles will 'burn' - do you think it's productive? It's just lactic acid/metabolic byproduct build up. And define working hard - you can work hard doing stupid stuff - that it's stupid means it doesn't matter if it's hard. It's ineffective. Smarter comes first. Because it just isn't. It has nothing to do with muscle growth. it's more about inflammation to connective tissue, often due to a novel eccentric stimulus. Performance. These are not metabolic workouts - you're not going to be cardiovascularly taxed like you would a metabolic workout. Depends on the person and their goals.