OK, so I don't want to get into body building but I do want to build some muscle. It's getting there slowly, but I heard that a calorie surplus is needed for this.

I'm a little confused about just how much this surplus is... and how much working out I'd have to do for it to turn to muscle and not fat! Do I aim for a surplus every day, or just on the days I work out? Is there a specific intensity at which I have to work-out to be able to go into surplus without gaining fat? I'm very paranoid of reversing or ruining what I *have* gained.

My current calories needed to maintain is just under 2000cal.