For all who do not speak german:
This article is about the aftereffects of sore muscles. Dr. Böning mentions that musclesoreness leads to hypertrophie- it is the decisive stimulus!
I have found a good way to train really hard. Believe me: this will make your muscles sore. And it won't take too long.
Choose a weight you can lift for 6-8 times. When you can't move the DB or BB any more try to keep the tension for 10-15 seconds more. Try to lift it!
Then rest for 10-20 seconds. Remove 2,5kg from your DB/BB and repeat step 1.
Try to do 20 reps. That's it. Your muscles will be sore as hell the next day!