Muscles do not grow during the workout session, They grow in recovery. Studies show that ONE SET per muscle group is enough to stimulate some growth. The problem when creating a training regiment is allocating the amount of volume you can do while prioritizing recovery. Others studies show that the last five reps before failure in a set are the most stimulating, so the rep ranges of 5-10 (often shortened to 6-8) is the most optimal for muscle growth while also creating the least amount of fatigue. Finally, when looking at a number of total sessions per muscle group in a week, the minimum required to grow muscle optimally is 2, and the maxiumum, in literature, is 18. realistically, for new and experienced lifters, recovery from 18 sets a week could be quite the task for the body to handle in a 4-5 day workout regiment. 8-12 sets a week per muscle group a week is usually the consensus on the correct amount of sets a week without creating too much fatigue for your body to recover from.