Question: how many reps and sets to gain muscle mass?
Answer: To gain muscle: Three or more sets of 6 to 8 reps to fatigue. For beginners, give yourself several weeks of conditioning before going to this level. You may need a spotter for many exercises. For health and endurance: One to 3 sets of 12 to 16 reps using enough weight that you can only complete the desired reps.