Question: how many reps and sets to build strength?
Answer: For muscular endurance, do two to three sets of 12 reps or more at 60 to 70 percent of your max. To gain muscle mass (hypertrophy), do three to six sets of six to 12 reps at 70 to 80 percent of your max. For muscular strength, do two to six sets of less than six reps at 80 to 90 percent of your max.