you do not need HEAVY weight/ Low reps to GROW muscle
Lets say you grab the weight that you can do 20 times and fail on the 21st. Without going to failure, keep doing as many sets as you can with that weight avoiding failure.You will see that with each progressive set your pump will be getting better and that it will be harder and harder to do the same amount of reps as your last set. This is because your muscles work according to the size principle. As you progress through the sets, your muscle fibers will be tiring out and new ones will be coming into the game. So you get the following:
1) You will work and fatigue a lot of muscle fibers
2) The pump with short rest periods between each set will be trapping causing the metabolic magic
3) You avoid failure and can do more volume
4) No need to use heavy weights to cause muscle fiber damage: *****://www.goodreads.com/author_blog_posts/6083371-bodybuilding--vs-powerlifting-type-training-which-builds-more-strength
so you use moderate weight, short rest period
breaking down muscle fibers is borderline a myth. There are some problems with that:
1) Muscle damage is not an indicator of muscle growth: [url]http://jeb.biologists.org/content/214/4/674.full.pdf[/url] , *****://www.jstage.jst.go.jp/article/ijshs/1/1/1_1_1/_article
2) Volume seems to be the deciding factor for causing muscle growth: *****://www.goodreads.com/author_blog_posts/6083371-bodybuilding--vs-powerlifting-type-training-which-builds-more-strength
3) Slow eccentrics is not necessary: [url]http://www.danogborn.com/training/sl.../#.U2ikhscYVDk[/url]
4) Muscle fiber principle dictates that muscles work together, there is no reason to separate them. High reps will also work the type II muscle fibers, given that cumulative fatigue will be achieved by doing work
5) Muscle failure is merely an event, not a prerequisite for muscle growth