What kind of exercise do you do if you want to gain muscle mass in a healthy way?

There is not specific exercise, but  if you want to gain mass in your muscles you have to be eating right. Certain types of foods to be able to gain that mass. Also you have to watch your calories simply to maintain your weights. You can do any kind of exercise, but the thing that will put mass in your muscles is the types of foods you eat to gain it.