To achieve what you want exercise and diet are equally important.
I used to work out without changing anything about the way I ate. While it did give me a bit more muscle and energy, the results were not what I had hoped for.
When I moved, I changed gym and the trainer there helped me figure out how to change my diet so I could get the most out of my workouts. For me that meant adding two "snacks" in between the main meals. With this advice and regular work outs 3-4 times a week, I went from 160lbs to 185lbs in six months.
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