Back in the early 90's bodybuilder JJ Marsh, who was known for his huge ripped thighs, said in a magazine that his thighs didn't explode into growth until he started squatting 3 times a week. So, being a dummy, I had to try it myself. I did just 5 sets of barbell squats followed by 5 sets of lying leg curls on M/W/F. It took about a month before I saw noticeable improvements in size. Mentally though, I burned out after doing it for about 6 or 7 weeks and went back to a normal routine.