"This is due to postural adaptations like shortening of the pectoralis major and minor muscle, internal rotation of the shoulders and an increased thoracic spinal curve called kyphosis." ...

They focused on the muscles involved in the exercise: pectoralis major, pectoralis minor, anterior deltoids, medial deltoids, and triceps brachii. Muscle hypertrophy refers to muscle growth or ...

But it needn't be that way. If you want huge pecs you'll need to challenge all of your chest muscles. But, you can't target all of your chest muscles if you don't know what they are, can you?