The quadriceps are primarily composed of the less powerful Type IIa fibers and as such respond best to higher reps. Just look at the impressive thigh development of speed skaters and cyclers, even in the distance events. One of the best high-rep squatters was Tom Platz. Platz, who finished third in the 1981 Mr. Olympia, had arguably the best thigh development of any bodybuilder…ever. He claims to have squatted 585 pounds for 23 reps.
Many authors of the Iron Game, have espoused this system to help trainees to gain mass, from Peary Rader to Randall Strossen.
Although many variations of this program exist, generally there is some type of warm-up and you perform only one all-out set of 20 reps. Also, it’s often recommended to take three deep breaths between each rep. What is actually happening when you take the breaths is that you’re doing 20 single-rep sets with about 10 seconds of rest between each rep. This rest enables you to recruit more higher-threshold motor units than you would if you did the 20 reps with minimal rest between sets. If you’re looking for a challenge and a quick way to pack on some muscle mass, then 20-rep squats are worth a try.