Building Muscle Mass The 2 factors that contribute to gaining weight and muscle mass are Diet and Exercise. Both are equally important.
Gaining weight You have just got to eat more calories than your body burns. To work out how many additional calories you need to eat, men should multiply their body weight by 15.
Women should multiply their body weight by 12. The result is the number of calories that you must consume each and every day while maintaining your existing level of activity. This will only maintain your existing body weight. To increase bodyweight eat an minimum of 500 EXTRA calories.
Most of us would like to be leaner and become stronger or just plain want to have bigger muscles all round. I got back into weight train after a lot of years off with one purpose to negate the effects of getting older.