Creating muscle mass requires a you to perform a different kind of workout than that which most people do. Building body mass is all about doing heavy weight lifting. Most people follow the 10-15 reps routine. This means that they’ve been told they should find a weight which they can do 10-15 times each set.
This is another case in which outdated information is passed around gyms as if it were gospel. It’s just like the fat spot reduction myth, or the way people believe that by doing endless cardio they will get the best fat loss results.
So, the first key to create muscle mass is to do heavy lifting. Aim for the 6-8 reps in each set. I’m not saying you should never do longer sets, but never fail to do some shorter ones to make sure the musles get the maximum stimulation.
Also, you need to make sure you’re not over-training some muscles group. One of the most common mistakes I see people make is spend the same time on big muscles group and small ones. There’s no reason to do 12 sets for your biceps if you’re doing the same for your back muscles. For one thing, the biceps play a supporting role in back exercises, and you may actually be working them too hard for your own good. The same is true for the chest and triceps.
Lastly, you shouldn’t do too much cardio. Cardio may not be the best thing if you wish to create the maximum amount of body mass. Of course, you should do cardio, but make sure that most of the energy you expend at the gym goes to strength workouts and not cardio.