This article is from the Hardgainer Bodybuilding & Weightlifting FAQ, by Frank J. Kelly and Craig R. Sadler with numerous contributions by others.
Simple:
Lots of weight + Lots of reps = Lots of muscle
This is only possible with the Deadlift and the Squat.
There is some evidence that the use of high reps in these
promotes the release of testosterone, possibly due to the
huge effort involved mentally and physically to take a
large weight to 20 reps (squat/dl) in good form.
 
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